Irreversible adsorption of particles on heterogeneous surfaces.

PubMed

Adamczyk, Zbigniew; Jaszczółt, Katarzyna; Michna, Aneta; Siwek, Barbara; Szyk-Warszyńska, Lilianna; Zembala, Maria

2005-12-30

Methods of theoretical and experimental evaluation of irreversible adsorption of particles, e.g., colloids and globular proteins at heterogeneous surfaces were reviewed. The theoretical models were based on the generalized random sequential adsorption (RSA) approach. Within the scope of these models, localized adsorption of particles occurring as a result of short-ranged attractive interactions with discrete adsorption sites was analyzed. Monte-Carlo type simulations performed according to this model enabled one to determine the initial flux, adsorption kinetics, jamming coverage and the structure of the particle monolayer as a function of the site coverage and the particle/site size ratio, denoted by lambda. It was revealed that the initial flux increased significantly with the site coverage theta(s) and the lambda parameter. This behavior was quantitatively interpreted in terms of the scaled particle theory. It also was demonstrated that particle adsorption kinetics and the jamming coverage increased significantly, at fixed site coverage, when the lambda parameter increased. Practically, for alpha = lambda2theta(s) > 1 the jamming coverage at the heterogeneous surfaces attained the value pertinent to continuous surfaces. The results obtained prove unequivocally that spherically shaped sites were more efficient in binding particles in comparison with disk-shaped sites. It also was predicted that for particle size ratio lambda < 4 the site multiplicity effect plays a dominant role, affecting significantly the structure of particle monolayers and the jamming coverage. Experimental results validating main aspects of these theoretical predictions also have been reviewed. These results were derived by using monodisperse latex particles adsorbing on substrates produced by covering uniform surface by adsorption sites of a desired size, coverage and surface charge. Particle deposition occurred under diffusion-controlled transport conditions and their coverage was

Mercury adsorption properties of sulfur-impregnated adsorbents

USGS Publications Warehouse

Hsi, N.-C.; Rood, M.J.; Rostam-Abadi, M.; Chen, S.; Chang, R.

2002-01-01

Carbonaceous and noncarbonaceous adsorbents were impregnated with elemental sulfur to evaluate the chemical and physical properties of the adsorbents and their equilibrium mercury adsorption capacities. Simulated coal combustion flue gas conditions were used to determine the equilibrium adsorption capacities for Hg0 and HgCl2 gases to better understand how to remove mercury from gas streams generated by coal-fired utility power plants. Sulfur was deposited onto the adsorbents by monolayer surface deposition or volume pore filling. Sulfur impregnation increased the total sulfur content and decreased the total and micropore surface areas and pore volumes for all of the adsorbents tested. Adsorbents with sufficient amounts of active adsorption sites and sufficient microporous structure had mercury adsorption capacities up to 4,509 ??g Hg/g adsorbent. Elemental sulfur, organic sulfur, and sulfate were formed on the adsorbents during sulfur impregnation. Correlations were established with R2>0.92 between the equilibrium Hg0/HgCl2 adsorption capacities and the mass concentrations of elemental and organic sulfur. This result indicates that elemental and organic sulfur are important active adsorption sites for Hg0 and HgCl2.

Application of low energy ion blocking for adsorption site determination of Na Atoms on a Cu(111) surface

NASA Astrophysics Data System (ADS)

Zhang, R.; Makarenko, B.; Bahrim, B.; Rabalais, J. W.

2010-07-01

Ion blocking in the low keV energy range is demonstrated to be a sensitive method for probing surface adsorption sites by means of the technique of time-of-flight scattering and recoiling spectroscopy (TOF-SARS). Adsorbed atoms can block the nearly isotropic backscattering of primary ions from surface atoms in the outmost layers of a crystal. The relative adsorption site position can be derived unambiguously by simple geometrical constructs between the adsorbed atom site and the surface atom sites. Classical ion trajectory simulations using the scattering and recoiling imaging code (SARIC) and molecular dynamics (MD) simulations provide the detailed ion trajectories. Herein we present a quantitative analysis of the blocking effects produced by sub-monolayer Na adsorbed on a Cu(111) surface at room temperature. The results show that the Na adsorption site preferences are different at different Na coverages. At a coverage θ = 0.25 monolayer, Na atoms preferentially populate the fcc threefold surface sites with a height of 2.7 ± 0.1 Å above the 1st layer Cu atoms. At a lower coverage of θ = 0.10 monolayer, there is no adsorption site preference for the Na atoms on the Cu(111) surface.

Kinetics of Cation and Oxyanion Adsorption and Desorption on Ferrihydrite: Roles of Ferrihydrite Binding Sites and a Unified Model.

PubMed

Tian, Lei; Shi, Zhenqing; Lu, Yang; Dohnalkova, Alice C; Lin, Zhang; Dang, Zhi

2017-09-19

Quantitative understanding the kinetics of toxic ion reactions with various heterogeneous ferrihydrite binding sites is crucial for accurately predicting the dynamic behavior of contaminants in environment. In this study, kinetics of As(V), Cr(VI), Cu(II), and Pb(II) adsorption and desorption on ferrihydrite was studied using a stirred-flow method, which showed that metal adsorption/desorption kinetics was highly dependent on the reaction conditions and varied significantly among four metals. High resolution scanning transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy showed that all four metals were distributed within the ferrihydrite aggregates homogeneously after adsorption reactions. Based on the equilibrium model CD-MUSIC, we developed a novel unified kinetics model applicable for both cation and oxyanion adsorption and desorption on ferrihydrite, which is able to account for the heterogeneity of ferrihydrite binding sites, different binding properties of cations and oxyanions, and variations of solution chemistry. The model described the kinetic results well. We quantitatively elucidated how the equilibrium properties of the cation and oxyanion binding to various ferrihydrite sites and the formation of various surface complexes controlled the adsorption and desorption kinetics at different reaction conditions and time scales. Our study provided a unified modeling method for the kinetics of ion adsorption/desorption on ferrihydrite.

Heavy metal adsorption changes of EAF steel slag after phosphorus adsorption.

PubMed

Song, Guanling; Cao, Lijing; Chen, Xiao; Hou, Wenhua; Wang, Qunhui

2012-01-01

A kind of electric arc furnace (EAF) steel slag was phosphated, and its isothermal and dynamic adsorptions of copper, cadmium, and lead ions were measured to determine if heavy metal adsorption changes after phosphorus adsorption. The surface area increased greatly after the slag was phosphated. Isothermal adsorption experiments showed that the theoretical Q(max) of the EAF steel slag on Cu(2+), Cd(2+), and Pb(2+) improved 59, 50, and 89% respectively after it was phosphated. Dynamic adsorption results showed that the greatest adsorption capacities of unit volume of Cu(2+), Cd(2+), and Pb(2+) were 2.2, 1.8, and 1.8 times that of the column packed with original EAF steel slag when the column was packed with phosphate EAF steel slag at the same heavy metal ion concentration. The breakthrough time, the exhaustion time and elution efficiency of the column also increased when the column was packed with phosphated EAF steel slag compared with that packed with original EAF steel slag. Phosphorus adsorption could further improve the heavy metal ion adsorption of the EAF steel slag.

Study of Adsorption Mechanism of Congo Red on Graphene Oxide/PAMAM Nanocomposite

PubMed Central

Rafi, Mohammad; Samiey, Babak; Cheng, Chil-Hung

2018-01-01

Graphene oxide/poly(amidoamine) (GO/PAMAM) nanocomposite adsorbed high quantities of congo red (CR) anionic dye in 0.1 M NaCl solution, with the maximum adsorption capacity of 198 mg·g−1. The kinetics and thermodynamics of adsorption were investigated to elucidate the effects of pH, temperature, shaking rate, ionic strength, and contact time. Kinetic data were analyzed by the KASRA model and the KASRA, ISO, and pore-diffusion equations. Adsorption adsorption isotherms were studied by the ARIAN model and the Henry, Langmuir, and Temkin equations. It was shown that adsorption sites of GO/PAMAM at experimental conditions were phenolic hydroxyl groups of GO sheets and terminal amine groups of PAMAM dendrimer. Analysis of kinetic data indicated that amine sites were located on the surface, and that hydroxyl sites were placed in the pores of adsorbent. CR molecules interacted with the adsorption sites via hydrogen bonds. The molecules were adsorbed firstly on the amine sites, and then on the internal hydroxyl sites. Adsorption kinetic parameters indicated that the interaction of CR to the –NH3+ sites was the rate-controlling step of adsorption of CR on this site and adsorption activation energies calculated for different parts of this step. On the other hand, kinetic parameters showed that the intraparticle diffusion was the rate-controlling step during the interaction of CR molecules to –OH sites and activation energy of this step was not calculable. Finally, the used GO/PAMAM was completely regenerated by using ethylenediamine. PMID:29587463

Water adsorption on goethite: Application of multilayer adsorption models

NASA Astrophysics Data System (ADS)

Hatch, C. D.; Tumminello, R.; Meredith, R.

2016-12-01

Adsorbed water on the surface of atmospheric mineral dust has recently been shown to significantly affect the ability of mineral dust aerosol to act as cloud condensation nuclei. We have studied water adsorption as a function of relative humidity (RH) on goethite (α-FeO(OH)), a common component of atmospheric mineral dust. The goethite surface area and particle size was determined using BET analysis and with N2 as an adsorbate and scanning electron microscopy, respectively. Water adsorption on the sample was monitored using horizontal attenuated total reflectance Fourier transform infrared (HATR-FTIR) spectroscopy equipped with a flow cell. Water content was determined using Beer's law and the optical constants for bulk water. The results were analyzed using Type II adsorption isotherms to model multilayer adsorption, including BET (Brunauer, Emmet and Teller), FHH (Frenkel, Halsey and Hill) and Freundlich. BET fits to experimental data provide parameters of monolayer coverage, while the FHH and Freundlich isotherms provide insights into multilayer adsorption mechanisms. Results indicate that goethite contains 5% H2O by mass at 50% RH, which increases to 12% by mass at 90% RH. Adsorption parameters and experimental results will be presented.

Wrinkles and Folds of Activated Graphene Nanosheets as Fast and Efficient Adsorptive Sites for Hydrophobic Organic Contaminants.

PubMed

Wang, Jun; Chen, Baoliang; Xing, Baoshan

2016-04-05

To create more wrinkles and folds as available adsorption sites, graphene nanosheets (GNS) were thermally treated with KOH for morphological alteration. The surface structures and properties of the activated graphene nanosheets (AGN) were characterized by BET-N2, SEM, TEM, Raman, XRD, XPS, and FTIR. After KOH etching, the highly crystal structure was altered, self-aggregation of graphene layers were evidently relieved, and more single to few layer graphene nanosheets were created with wrinkles and folds. Also both specific surface area and micropore volume of AGN increased relative to GNS. The adsorption of AGN toward p-nitrotoluene, naphthalene and phenanthrene were greatly enhanced in comparison with GNS, and gradually promoted with increasing degree of KOH etching. Adsorption rate of organic contaminants on AGN was very fast and efficient, whereas small molecules showed higher adsorption rates due to the more porous surface of graphene. In addition to π-π interaction, the high affinities of p-nitrotoluene to AGN are suggested from strong electron charge transfer interactions between nitro groups on p-nitrotoluene and defect sites of AGN. A positively linear correlation between organic molecule uptake and the micropore volume of AGN indicated that pore-filling mechanism may play an important role in adsorption. Morphological wrinkles and folds of graphene nanosheets can be regulated to enhance the adsorption capability and kinetics for efficient pollutant removal and to selectively preconcentrate adsorbates with different sizes for detection.

Contrasting nitrate adsorption in Andisols of two coffee plantations in Costa Rica.

PubMed

Ryan, M C; Graham, G R; Rudolph, D L

2001-01-01

Fertilizer use in coffee plantations is a suspected cause of rising ground water nitrate concentrations in the ground water-dependent Central Valley of Costa Rica. Nitrate adsorption was evaluated beneath two coffee (Coffea arabica L.) plantations in the Central Valley. Previous work at one site had identified unsaturated zone nitrate retardation relative to a tritium tracer. Differences in nitrate adsorption were assessed in cores to 4 m depth in Andisols at this and one other plantation using differences in KCl- and water-extractable nitrate as an index. Significant adsorption was confirmed at the site of the previous tracer test, but not at the second site. Anion exchange capacity, X-ray diffraction data, extractable Al and Si, and soil pH in NaF corroborated that differences in adsorption characteristics were related to subtle differences in clay mineralogy. Soils at the site with significant nitrate adsorption showed an Al-rich allophane clay content compared with a more weathered, Si-rich allophane and halloysite clay mineral content at the site with negligible adsorption. At the site with significant nitrate adsorption, nitrate occupied less than 10% of the total anion adsorption capacity, suggesting that adsorption may provide long-term potential for mitigation or delay of nitrate leaching. Evaluation of nitrate sorption potential of soil at local and landscape scales would be useful in development of nitrogen management practices to reduce nitrate leaching to ground water.

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

PubMed

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

2013-09-04

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

Adsorptive Removal and Adsorption Kinetics of Fluoroquinolone by Nano-Hydroxyapatite

PubMed Central

Chen, Yajun; Lan, Tao; Duan, Lunchao; Wang, Fenghe; Zhao, Bin; Zhang, Shengtian; Wei, Wei

2015-01-01

Various kinds of antibiotics, especially fluoroquinolone antibiotics (FQs) have been widely used for the therapy of infectious diseases in human and livestock. For their poorly absorbed by living organisms, large-scale misuse or abuse of FQs will foster drug resistance among pathogenic bacteria, as well as a variety of environmental problems when they were released in the environment. In this work, the adsorption properties of two FQs, namely norfloxacin (NOR) and ciprofloxacin (CIP), by nano-hydroxyapatite (n-HAP) were studied by batch adsorption experiments. The adsorption curves of FQs by n-HAP were simulated by Langmuir and Freundlich isotherms. The results shown that NOR and CIP can be adsorbed effectively by the adsorbent of n-HAP, and the adsorption capacity of FQs increase with increasing dosage of n-HAP. The optimum dosage of n-HAP for FQs removal was 20 g·L-1, in which the removal efficiencies is 51.6% and 47.3%, and an adsorption equilibrium time is 20 min. The maximum removal efficiency occurred when pH is 6 for both FQs. The adsorption isotherm of FQs fits well for both Langmuir and Freundlich equations. The adsorption of both FQs by n-HAP follows second-order kinetics. PMID:26698573

Modeling of Cd adsorption to goethite-bacteria composites

DOE PAGES

Qu, Chenchen; Ma, Mingkai; Chen, Wenli; ...

2017-11-21

The accurate modeling of heavy metal adsorption in complex systems is fundamental for risk assessments in soils and associated environments. Bacteria-iron (hydr)oxide associations in soils and sediments play a critical role in heavy metal immobilization. The reduced adsorption of heavy metals on these composites have been widely reported using the component additivity (CA) method. However, there is a lack of a mechanism model to account for these deviations. In this study, we established models for Cd adsorption on goethite-Pseudomonas putida composites at 1:1 and 5:1 mass ratios. Cadmium adsorption on the 5:1 composite was consistent with the additivity method. But,more » the CA method over predicted Cd adsorption by approximately 8% on the 1:1 composite at high Cd concentration. The deviation was corrected by adding the site blockage reactions between P. putida and goethite. Both CA and “CA-site masking” models for Cd adsorption onto the composites were in line with the ITC data. These results indicate that CA method in simulating Cd adsorption on bacteria-iron oxides composites is limited to low bacterial and Cd concentrations. Thus the interfacial complexation reactions that occur between iron (hydr)oxides and bacteria should be taken into account when high concentrations of bacteria and heavy metals are present.« less

Modeling of Cd adsorption to goethite-bacteria composites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qu, Chenchen; Ma, Mingkai; Chen, Wenli

The accurate modeling of heavy metal adsorption in complex systems is fundamental for risk assessments in soils and associated environments. Bacteria-iron (hydr)oxide associations in soils and sediments play a critical role in heavy metal immobilization. The reduced adsorption of heavy metals on these composites have been widely reported using the component additivity (CA) method. However, there is a lack of a mechanism model to account for these deviations. In this study, we established models for Cd adsorption on goethite-Pseudomonas putida composites at 1:1 and 5:1 mass ratios. Cadmium adsorption on the 5:1 composite was consistent with the additivity method. But,more » the CA method over predicted Cd adsorption by approximately 8% on the 1:1 composite at high Cd concentration. The deviation was corrected by adding the site blockage reactions between P. putida and goethite. Both CA and “CA-site masking” models for Cd adsorption onto the composites were in line with the ITC data. These results indicate that CA method in simulating Cd adsorption on bacteria-iron oxides composites is limited to low bacterial and Cd concentrations. Thus the interfacial complexation reactions that occur between iron (hydr)oxides and bacteria should be taken into account when high concentrations of bacteria and heavy metals are present.« less

Adsorption Refrigeration System

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Kai; Vineyard, Edward Allan

Adsorption refrigeration is an environmentally friendly cooling technology which could be driven by recovered waste heat or low-grade heat such as solar energy. In comparison with absorption system, an adsorption system has no problems such as corrosion at high temperature and salt crystallization. In comparison with vapor compression refrigeration system, it has the advantages of simple control, no moving parts and less noise. This paper introduces the basic theory of adsorption cycle as well as the advanced adsorption cycles such as heat and mass recovery cycle, thermal wave cycle and convection thermal wave cycle. The types, characteristics, advantages and drawbacksmore » of different adsorbents used in adsorption refrigeration systems are also summarized. This article will increase the awareness of this emerging cooling technology among the HVAC engineers and help them select appropriate adsorption systems in energy-efficient building design.« less

A flow-pulse adsorption-microcalorimetry system for studies of adsorption processes on powder catalysts

NASA Astrophysics Data System (ADS)

You, Rui; Li, Zhaorui; Zeng, Hongyu; Huang, Weixin

2018-06-01

A pulse chemisorption system combining a Tian-Calvet microcalorimeter (Setaram Sensys EVO 600) and an automated chemisorption apparatus (Micromeritics Autochem II 2920) was established to accurately measure differential adsorption heats of gas molecules' chemisorption on solid surfaces in a flow-pulse mode. Owing to high sensitivity and high degree of automation in a wide range of temperatures from -100 to 600 °C, this coupled system can present adsorption heats as a function of adsorption temperature and adsorbate coverage. The functions of this system were demonstrated by successful measurements of CO adsorption heats on Pd surfaces at various temperatures and also at different CO coverages by varying the CO concentration in the pulse dose. Key parameters, including adsorption amounts, integral adsorption heats, and differential adsorption heats of CO adsorption on a Pd/CeO2 catalyst, were acquired. Our adsorption-microcalorimetry system provides a powerful technique for the investigation of adsorption processes on powder catalysts.

Apparatus for thermal swing adsorption and thermally-enhanced pressure swing adsorption

DOEpatents

Wegeng, Robert S.; Rassat, Scot D.; Stenkamp, Victoria S.; TeGrotenhuis, Ward E.; Matson, Dean W.; Drost, M. Kevin; Viswanathan, Vilayanur V.

2005-12-13

The present invention provides compact adsorption systems that are capable of rapid temperature swings and rapid cycling. Novel methods of thermal swing adsorption and thermally-enhanced pressure swing adsorption are also described. In some aspects of the invention, a gas is passed through the adsorbent thus allowing heat exchangers to be very close to all portions of the adsorbent and utilize less space. In another aspect, the adsorption media is selectively heated, thus reducing energy costs. Methods and systems for gas adsorption/desorption having improved energy efficiency with capability of short cycle times are also described. Advantages of the invention include the ability to use (typically) 30-100 times less adsorbent compared to conventional systems.

Method for thermal swing adsorption and thermally-enhanced pressure swing adsorption

DOEpatents

Wegeng, Robert S.; Rassat, Scot D.; Stenkamp, Victoria S.; TeGrotenhuis, Ward E.; Matson, Dean W.; Drost, M. Kevin; Viswanathan, Vilayanur V.

2003-10-07

The present invention provides compact adsorption systems that are capable of rapid temperature swings and rapid cycling. Novel methods of thermal swing adsorption and thermally-enhanced pressure swing adsorption are also described. In some aspects of the invention, a gas is passed through the adsorbent thus allowing heat exchangers to be very close to all portions of the adsorbent and utilize less space. In another aspect, the adsorption media is selectively heated, thus reducing energy costs. Methods and systems for gas adsorption/desorption having improved energy efficiency with capability of short cycle times are also described. Advantages of the invention include the ability to use (typically) 30-100 times less adsorbent compared to conventional systems.

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

USGS Publications Warehouse

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

2009-01-01

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

Molecular Dynamics Simulation of Resin Adsorption at Kaolinite Edge Sites: Effect of Surface Deprotonation on Interfacial Structure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zeitler, T. R.; Greathouse, J. A.; Cygan, R. T.

Low-salinity water flooding, a method of enhanced oil recovery, consists of injecting low ionic strength fluids into an oil reservoir in order to detach oil from mineral surfaces in the underlying formation. Although highly successful in practice, the approach is not completely understood at the molecular scale. Molecular dynamics simulations have been used to investigate the effect of surface protonation on the adsorption of an anionic crude oil component on clay mineral edge surfaces. A set of interatomic potentials appropriate for edge simulations has been applied to the kaolinite (010) surface in contact with an aqueous nanopore. Decahydro-2-napthoic acid inmore » its deprotonated form (DHNA –) was used as a representative resin component of crude oil, with monovalent and divalent counterions, to test the observed trends in low-salinity water flooding experiments. Surface models include fully protonated (neutral) and deprotonated (negative) edge sites, which require implementation of a new deprotonation scheme. The surface adsorptive properties of the kaolinite edge under neutral and deprotonated conditions have been investigated for low and high DHNA – concentrations with Na + and Ca 2+ as counterions. The tendency of DHNA – ions to coordinate with divalent (Ca 2+) rather than monovalent (Na +) ions greatly influences adsorption tendencies of the anion. Additionally, the formation of net positively charged surface sites due to Ca 2+ at deprotonated sites results in increased DHNA – adsorption. Divalent cations such as Ca 2+ are able to efficiently bridge surface sites and organic anions. Replacing those cations with monovalent cations such as Na + diminishes the bridging mechanism, resulting in reduced adsorption of the organic species. As a result, a clear trend of decreased DHNA – adsorption is observed in the simulations as Ca 2+ is replaced by Na + for deprotonated surfaces, as would be expected for oil detachment from reservoir formations

Molecular Dynamics Simulation of Resin Adsorption at Kaolinite Edge Sites: Effect of Surface Deprotonation on Interfacial Structure

DOE PAGES

Zeitler, T. R.; Greathouse, J. A.; Cygan, R. T.; ...

2017-10-05

Low-salinity water flooding, a method of enhanced oil recovery, consists of injecting low ionic strength fluids into an oil reservoir in order to detach oil from mineral surfaces in the underlying formation. Although highly successful in practice, the approach is not completely understood at the molecular scale. Molecular dynamics simulations have been used to investigate the effect of surface protonation on the adsorption of an anionic crude oil component on clay mineral edge surfaces. A set of interatomic potentials appropriate for edge simulations has been applied to the kaolinite (010) surface in contact with an aqueous nanopore. Decahydro-2-napthoic acid inmore » its deprotonated form (DHNA –) was used as a representative resin component of crude oil, with monovalent and divalent counterions, to test the observed trends in low-salinity water flooding experiments. Surface models include fully protonated (neutral) and deprotonated (negative) edge sites, which require implementation of a new deprotonation scheme. The surface adsorptive properties of the kaolinite edge under neutral and deprotonated conditions have been investigated for low and high DHNA – concentrations with Na + and Ca 2+ as counterions. The tendency of DHNA – ions to coordinate with divalent (Ca 2+) rather than monovalent (Na +) ions greatly influences adsorption tendencies of the anion. Additionally, the formation of net positively charged surface sites due to Ca 2+ at deprotonated sites results in increased DHNA – adsorption. Divalent cations such as Ca 2+ are able to efficiently bridge surface sites and organic anions. Replacing those cations with monovalent cations such as Na + diminishes the bridging mechanism, resulting in reduced adsorption of the organic species. As a result, a clear trend of decreased DHNA – adsorption is observed in the simulations as Ca 2+ is replaced by Na + for deprotonated surfaces, as would be expected for oil detachment from reservoir formations

Adsorption of polycyclic aromatic hydrocarbons by graphene and graphene oxide nanosheets.

PubMed

Wang, Jun; Chen, Zaiming; Chen, Baoliang

2014-05-06

The adsorption of naphthalene, phenanthrene, and pyrene onto graphene (GNS) and graphene oxide (GO) nanosheets was investigated to probe the potential adsorptive sites and molecular mechanisms. The microstructure and morphology of GNS and GO were characterized by elemental analysis, XPS, FTIR, Raman, SEM, and TEM. Graphene displayed high affinity to the polycyclic aromatic hydrocarbons (PAHs), whereas GO adsorption was significantly reduced after oxygen-containing groups were attached to GNS surfaces. An unexpected peak was found in the curve of adsorption coefficients (Kd) with the PAH equilibrium concentrations. The hydrophobic properties and molecular sizes of the PAHs affected the adsorption of G and GO. The high affinities of the PAHs to GNS are dominated by π-π interactions to the flat surface and the sieving effect of the powerful groove regions formed by wrinkles on GNS surfaces. In contrast, the adsorptive sites of GO changed to the carboxyl groups attaching to the edges of GO because the groove regions disappeared and the polar nanosheet surfaces limited the π-π interactions. The TEM and SEM images initially revealed that after loading with PAH, the conformation and aggregation of GNS and GO nanosheets dramatically changed, which explained the observations that the potential adsorption sites of GNS and GO were unusually altered during the adsorption process.

Water adsorption constrained Frenkel-Halsey-Hill adsorption activation theory: Montmorillonite and illite

NASA Astrophysics Data System (ADS)

Hatch, Courtney D.; Greenaway, Ann L.; Christie, Matthew J.; Baltrusaitis, Jonas

2014-04-01

Fresh mineral aerosol has recently been found to be effective cloud condensation nuclei (CCN) and contribute to the number of cloud droplets in the atmosphere due to the effect of water adsorption on CCN activation. The work described here uses experimental water adsorption measurements on Na-montmorillonite and illite clay to determine empirical adsorption parameters that can be used in a recently derived theoretical framework (Frenkel-Halsey-Hill Activation Theory, FHH-AT) that accounts for the effect of water adsorption on CCN activation. Upon fitting the Frenkel-Halsey-Hill (FHH) adsorption model to water adsorption measurements, we find FHH adsorption parameters, AFHH and BFHH, to be 98 ± 22 and 1.79 ± 0.11 for montmorillonite and 75 ± 17 and 1.77 ± 0.11 for illite, respectively. The AFHH and BFHH values obtained from water adsorption measurements differ from values reported previously determined by applying FHH-AT to CCN activation measurements. Differences in FHH adsorption parameters were attributed to different methods used to obtain them and the hydratable nature of the clays. FHH adsorption parameters determined from water adsorption measurements were then used to calculate the critical super-saturation (sc) for CCN activation using FHH-AT. The relationship between sc and the dry particle diameter (Ddry) gave CCN activation curve exponents (xFHH) of -0.61 and -0.64 for montmorillonite and illite, respectively. The xFHH values were slightly lower than reported previously for mineral aerosol. The lower exponent suggests that the CCN activity of hydratable clays is less sensitive to changes in Ddry and the hygroscopicity parameter exhibits a broader variability with Ddry compared to more soluble aerosols. Despite the differences in AFHH, BFHH and xFHH, the FHH-AT derived CCN activities of montmorillonite and illite are quite similar to each other and in excellent agreement with experimental CCN measurements resulting from wet-generated clay aerosol

Adsorption and Dissociation of Molecular Hydrogen on the (0001) Surface of DHCP Americium

NASA Astrophysics Data System (ADS)

Dholabhai, Pratik; Ray, Asok

2009-03-01

Hydrogen molecule adsorption on the (0001) surface of double hexagonal closed packed americium has been studied in detail within the framework of density functional theory. Weak molecular hydrogen adsorptions were observed. The most stable configuration corresponded to a Hor2 approach molecular adsorption at the one-fold top site where the molecule's approach is perpendicular to a lattice vector. Adsorption energies and adsorption geometries for different adsorption sites will be discussed. The change in work functions, magnetic moments, partial charges inside muffin-tins, difference charge density distributions and density of states for the bare Am slab and the Am slab after adsorption of the hydrogen molecule will be discussed. Reaction barrier for the dissociation of hydrogen molecule will be presented. The implications of adsorption on Am 5f electron localization-delocalization will be summarized.

Adsorption of aqueous copper on peanut hulls

NASA Astrophysics Data System (ADS)

Davis, Kanika Octavia

A method was established for measuring the adsorption of Cu(II) from aqueous solution to unmodified and modified peanut hulls at constant temperature and pH. Modification of the hulls was performed by oxidation with alkaline hydrogen peroxide. During the modification process, the hydrogen peroxide solubilizes the lignin component, making the surface more porous which increases the availability of binding sites, while simultaneously oxidizing the cellulose. The oxidation of alcohol groups creates more binding sites by creating functional groups such as COO-, which increases chelation to metal ions. Fourier transform infrared spectroscopy confirms delignification of the peanut hulls by the disappearance of carboxyl peaks of the modified hulls, which were originally produced from the lignin content. Although, oxidation is not fully confirmed, it is not ruled out because the expected carboxylate peak (1680 cm-1) maybe overshadowed by a broad peak due to OH bending of water adsorbed to the hulls. Hulls adsorbed copper from solutions in the concentration range of 50-1000 ppm of CuCl2. Concentrations of pre- and post-adsorption solutions were determined using inductively coupled plasma optical emission spectroscopy. The adsorption isotherms were fit to known two and three-parameter models, evaluated and the binding mechanism was inferred. Maximum surface coverage was 3.5 +/- 0.6 mg Cu2+ /g hull for unmodified hulls and 11 +/- 1 mg Cu2+/g hull for modified hulls. The adsorption for the hulls is best described by the Langmuir model, suggesting monolayer, homogeneous adsorption. With a free energy of adsorption of 10.5 +/- 0.9 kJ/mol for unmodified hulls and 14.5 +/-0.4 kJ/mol for modified hulls, the process is categorized as chemisorption for both types of hulls. The adsorption for both hulls is also described by the Redlich-Peterson model, giving beta nearer to 1 than 0, which further suggests homogeneous adsorption described by the Langmuir model. After rinsing the hulls

Adsorption of selenium by amorphous iron oxyhydroxide and manganese dioxide

USGS Publications Warehouse

Balistrieri, L.S.; Chao, T.T.

1990-01-01

This work compares and models the adsorption of selenium and other anions on a neutral to alkaline surface (amorphous iron oxyhydroxide) and an acidic surface (manganese dioxide). Selenium adsorption on these oxides is examined as a function of pH, particle concentration, oxidation state, and competing anion concentration in order to assess how these factors might influence the mobility of selenium in the environment. The data indicate that 1. 1) amorphous iron oxyhydroxide has a greater affinity for selenium than manganese dioxide, 2. 2) selenite [Se(IV)] adsorption increases with decreasing pH and increasing particle concentration and is stronger than selenate [Se(VI)] adsorption on both oxides, and 3. 3) selenate does not adsorb on manganese dioxide. The relative affinity of selenate and selenite for the oxides and the lack of adsorption of selenate on a strongly acidic surface suggests that selenate forms outer-sphere complexes while selenite forms inner-sphere complexes with the surfaces. The data also indicate that the competition sequence of other anions with respect to selenite adsorption at pH 7.0 is phosphate > silicate > molybdate > fluoride > sulfate on amorphous iron oxyhydroxide and molybdate ??? phosphate > silicate > fluoride > sulfate on manganese dioxide. The adsorption of phosphate, molybdate, and silicate on these oxides as a function of pH indicates that the competition sequences reflect the relative affinities of these anions for the surfaces. The Triple Layer surface complexation model is used to provide a quantitative description of these observations and to assess the importance of surface site heterogeneity on anion adsorption. The modeling results suggest that selenite forms binuclear, innersphere complexes with amorphous iron oxyhydroxide and monodentate, inner-sphere complexes with manganese dioxide and that selenate forms outer-sphere, monodentate complexes with amorphous iron oxyhydroxide. The heterogeneity of the oxide surface sites

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

PubMed

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

2014-07-15

Antimony is detected in soil and water with elevated concentration due to a variety of industrial applications and mining activities. Though antimony is classified as a pollutant of priority interest by the United States Environmental Protection Agency (USEPA) and Europe Union (EU), very little is known about its environmental behavior and adsorption mechanism. In this study, the adsorption behaviors and surface structure of antimony (III/V) on iron oxides were investigated using batch adsorption techniques, surface complexation modeling (SCM), X-ray photon spectroscopy (XPS) and extended X-ray absorption fine structure spectroscopy (EXAFS). The adsorption isotherms and edges indicated that the affinity of Sb(V) and Sb(III) toward the iron oxides depended on the Sb species, solution pH, and the characteristics of iron oxides. Sb(V) adsorption was favored at acidic pH and decreased dramatically with increasing pH, while Sb(III) adsorption was constant over a broad pH range. When pH is higher than 7, Sb(III) adsorption by goethite and hydrous ferric oxide (HFO) was greater than Sb(V). EXAFS analysis indicated that the majority of Sb(III), either adsorbed onto HFO or co-precipitated by FeCl3, was oxidized into Sb(V) probably due to the involvement of O2 in the long duration of sample preservation. Only one Sb-Fe subshell was filtered in the EXAFS spectra of antimony adsorption onto HFO, with the coordination number of 1.0-1.9 attributed to bidentate mononuclear edge-sharing ((2)E) between Sb and HFO. Copyright © 2014 Elsevier B.V. All rights reserved.

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

USGS Publications Warehouse

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

1993-01-01

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

Probing adsorption sites of carbon dioxide in metal organic framework of [Zn(bdc)(dpds)]n: A molecular simulation study

NASA Astrophysics Data System (ADS)

Lu, Shih-I.; Liao, Jian-Min; Huang, Xiao-Zhuang; Lin, Chia-Hsun; Ke, Szu-Yu; Wang, Chih-Chieh

2017-11-01

We used force-field based grand-canonical Monte Carlo simulation method and density functional theory to study adsorption characteristics of carbon dioxide (CO2) molecules in a metal-organic framework (MOF) compound, [Zn(bdc)(dpds)]n. The studied MOF include a metal ion (Zn(II)), an anion organic linker (dianion of benzene dicarboxylicacid, bdc2-) and a neutral organic linker (4,4‧-dipyridyldisulfide, dpds). Results from calculated adsorption isotherms and enthalpies of adsorption agree with the experimental data. The interactions between the adsorbed CO2 and the organic linkers were examined in simulations. Calculated results show available absorption sites are surrounded by two dpds ligands in which an S-S bond as an N-N‧ spacer connect two pyridines. In contrast, the bdc2- ligand does not give a significant contribution to the substantial adsorption amount even though it contains the carboxylate group that provides available bonding site to CO2.

Albumin (BSA) adsorption onto graphite stepped surfaces

NASA Astrophysics Data System (ADS)

Rubio-Pereda, Pamela; Vilhena, J. G.; Takeuchi, Noboru; Serena, Pedro A.; Pérez, Rubén

2017-06-01

Nanomaterials are good candidates for the design of novel components with biomedical applications. For example, nano-patterned substrates may be used to immobilize protein molecules in order to integrate them in biosensing units. Here, we perform long MD simulations (up to 200 ns) using an explicit solvent and physiological ion concentrations to characterize the adsorption of bovine serum albumin (BSA) onto a nano-patterned graphite substrate. We have studied the effect of the orientation and step size on the protein adsorption and final conformation. Our results show that the protein is stable, with small changes in the protein secondary structure that are confined to the contact area and reveal the influence of nano-structuring on the spontaneous adsorption, protein-surface binding energies, and protein mobility. Although van der Waals (vdW) interactions play a dominant role, our simulations reveal the important role played by the hydrophobic lipid-binding sites of the BSA molecule in the adsorption process. The complex structure of these sites, that incorporate residues with different hydrophobic character, and their flexibility are crucial to understand the influence of the ion concentration and protein orientation in the different steps of the adsorption process. Our study provides useful information for the molecular engineering of components that require the immobilization of biomolecules and the preservation of their biological activity.

Removal of carbonyl sulfide using activated carbon adsorption.

PubMed

Sattler, Melanie L; Rosenberk, Ranjith Samuel

2006-02-01

Wastewater treatment plant odors are caused by compounds such as hydrogen sulfide (H2S), methyl mercaptans, and carbonyl sulfide (COS). One of the most efficient odor control processes is activated carbon adsorption; however, very few studies have been conducted on COS adsorption. COS is not only an odor causing compound but is also listed in the Clean Air Act as a hazardous air pollutant. Objectives of this study were to determine the following: (1) the adsorption capacity of 3 different carbons for COS removal; (2) the impact of relative humidity (RH) on COS adsorption; (3) the extent of competitive adsorption of COS in the presence of H2S; and (4) whether ammonia injection would increase COS adsorption capacity. Vapor phase react (VPR; reactivated), BPL (bituminous coal-based), and Centaur (physically modified to enhance H2S adsorption) carbons manufactured by Calgon Carbon Corp. were tested in three laboratory-scale columns, 6 in. in depth and 1 in. in diameter. Inlet COS concentrations varied from 35 to 49 ppmv (86-120 mg/m3). RHs of 17%, 30%, 50%, and 90% were tested. For competitive adsorption studies, H2S was tested at 60 ppmv, with COS at 30 ppmv. COS, RH, H2S, and ammonia concentrations were measured using an International Sensor Technology Model IQ-350 solid state sensor, Cole-Parmer humidity stick, Interscan Corp. 1000 series portable analyzer, and Drager Accuro ammonia sensor, respectively. It was found that the adsorption capacity of Centaur carbon for COS was higher than the other two carbons, regardless of RH. As humidity increased, the percentage of decrease in adsorption capacity of Centaur carbon, however, was greater than the other two carbons. The carbon adsorption capacity for COS decreased in proportion to the percentage of H2S in the gas stream. More adsorption sites appear to be available to H2S, a smaller molecule. Ammonia, which has been found to increase H2S adsorption capacity, did not increase the capacity for COS.

NH3 adsorption on anatase-TiO2(101)

NASA Astrophysics Data System (ADS)

Koust, Stig; Adamsen, Kræn C.; Kolsbjerg, Esben Leonhard; Li, Zheshen; Hammer, Bjørk; Wendt, Stefan; Lauritsen, Jeppe V.

2018-03-01

The adsorption of ammonia on anatase TiO2 is of fundamental importance for several catalytic applications of TiO2 and for probing acid-base interactions. Utilizing high-resolution scanning tunneling microscopy (STM), synchrotron X-ray photoelectron spectroscopy, temperature-programmed desorption (TPD), and density functional theory (DFT), we identify the adsorption mode and quantify the adsorption strength on the anatase TiO2(101) surface. It was found that ammonia adsorbs non-dissociatively as NH3 on regular five-fold coordinated titanium surface sites (5f-Ti) with an estimated exothermic adsorption energy of 1.2 eV for an isolated ammonia molecule. For higher adsorbate coverages, the adsorption energy progressively shifts to smaller values, due to repulsive intermolecular interactions. The repulsive adsorbate-adsorbate interactions are quantified using DFT and autocorrelation analysis of STM images, which both showed a repulsive energy of ˜50 meV for nearest neighbor sites and a lowering in binding energy for an ammonia molecule in a full monolayer of 0.28 eV, which is in agreement with TPD spectra.

Adsorption of calcitonin to glass.

PubMed

Law, S L; Shih, C L

1999-02-01

Surface adsorption of calcitonin on soda lime silica glass was investigated. An attempt was also made to examine the effect of additives on the inhibition of calcitonin adsorption. Results showed that the adsorption isotherms were of the Langmuir and Freundlich type, depending on pH. Less adsorption was found for calcitonin at pH 4.3. The addition of nonionic surfactants such as Pluronic F68 and Tween 80 to the calcitonin solutions demonstrated inhibition of absorption and reduction of adsorption rate. The addition of chlorobutanol also showed the effect of minimizing adsorption.

Adsorption characteristics of siloxanes in landfill gas by the adsorption equilibrium test.

PubMed

Nam, Sangchul; Namkoong, Wan; Kang, Jeong-Hee; Park, Jin-Kyu; Lee, Namhoon

2013-10-01

Due to the increase in energy cost by constantly high oil prices and the obligation to reduce greenhouse effect gases, landfill gas is frequently used as an alternative energy source for producing heat and electricity. Most of landfill gas utility facilities, however, are experiencing problems controlling siloxanes from landfill gas as their catalytic oxidizers are becoming fouled by silicon dioxide dust. To evaluate adsorption characteristics of siloxanes, an adsorption equilibrium test was conducted and parameters in the Freundlich and Langmuir isotherms were analyzed. Coconut activated carbon (CA1), coal activated carbon (CA2), impregnated activated carbon (CA3), silicagel (NCA1), and activated alumina (NCA2) were used for the adsorption of the mixed siloxane which contained hexamethyldisiloxane (L2), octamethylcyclotetrasiloxane (D4), and decamethylcyclopentasiloxane (D5). L2 had higher removal efficiency in noncarbon adsorbents compared to carbon adsorbents. The application of Langmuir and Freundlich adsorption isotherm demonstrated that coconut based CA1 and CA3 provided higher adsorption capacity on L2. And CA2 and NCA1 provided higher adsorption capacity on D4 and D5. Based on the experimental results, L2, D4, and D5 were converted by adsorption and desorption in noncarbon adsorbents. Adsorption affinity of siloxane is considered to be affect by the pore size distribution of the adsorbents and by the molecular size of each siloxane. Copyright © 2013 Elsevier Ltd. All rights reserved.

Kinetics of Cd(ii) adsorption and desorption on ferrihydrite: experiments and modeling.

PubMed

Liang, Yuzhen; Tian, Lei; Lu, Yang; Peng, Lanfang; Wang, Pei; Lin, Jingyi; Cheng, Tao; Dang, Zhi; Shi, Zhenqing

2018-05-15

The kinetics of Cd(ii) adsorption/desorption on ferrihydrite is an important process affecting the fate, transport, and bioavailability of Cd(ii) in the environment, which was rarely systematically studied and understood at quantitative levels. In this work, a combination of stirred-flow kinetic experiments, batch adsorption equilibrium experiments, high-resolution transmission electron microscopy (HR-TEM), and mechanistic kinetic modeling were used to study the kinetic behaviors of Cd(ii) adsorption/desorption on ferrihydrite. HR-TEM images showed the open, loose, and sponge-like structure of ferrihydrite. The batch adsorption equilibrium experiments revealed that higher pH and initial metal concentration increased Cd(ii) adsorption on ferrihydrite. The stirred-flow kinetic results demonstrated the increased adsorption rate and capacity as a result of the increased pH, influent concentration, and ferrihydrite concentration. The mechanistic kinetic model successfully described the kinetic behaviors of Cd(ii) during the adsorption and desorption stages under various chemistry conditions. The model calculations showed that the adsorption rate coefficients varied as a function of solution chemistry, and the relative contributions of the weak and strong ferrihydrite sites for Cd(ii) binding varied with time at different pH and initial metal concentrations. Our model is able to quantitatively assess the contributions of each individual ferrihydrite binding site to the overall Cd(ii) adsorption/desorption kinetics. This study provided insights into the dynamic behavior of Cd(ii) and a predictive modeling tool for Cd(ii) adsorption/desorption kinetics when ferrihydrite is present, which may be helpful for the risk assessment and management of Cd contaminated sites.

Hydrogen adsorption strength and sites in the metal organic framework MOF5: Comparing experiment and model calculations

NASA Astrophysics Data System (ADS)

Mulder, F. M.; Dingemans, T. J.; Schimmel, H. G.; Ramirez-Cuesta, A. J.; Kearley, G. J.

2008-07-01

Hydrogen adsorption in porous, high surface area, and stable metal organic frameworks (MOF's) appears a novel route towards hydrogen storage materials [N.L. Rosi, J. Eckert, M. Eddaoudi, D.T. Vodak, J. Kim, M. O'Keeffe, O.M. Yaghi, Science 300 (2003) 1127; J.L.C. Rowsell, A.R. Millward, K. Sung Park, O.M. Yaghi, J. Am. Chem. Soc. 126 (2004) 5666; G. Ferey, M. Latroche, C. Serre, F. Millange, T. Loiseau, A. Percheron-Guegan, Chem. Commun. (2003) 2976; T. Loiseau, C. Serre, C. Huguenard, G. Fink, F. Taulelle, M. Henry, T. Bataille, G. Férey, Chem. Eur. J. 10 (2004) 1373]. A prerequisite for such materials is sufficient adsorption interaction strength for hydrogen adsorbed on the adsorption sites of the material because this facilitates successful operation under moderate temperature and pressure conditions. Here we report detailed information on the geometry of the hydrogen adsorption sites, based on the analysis of inelastic neutron spectroscopy (INS). The adsorption energies for the metal organic framework MOF5 equal about 800 K for part of the different sites, which is significantly higher than for nanoporous carbon materials (˜550 K) [H.G. Schimmel, G.J. Kearley, M.G. Nijkamp, C.T. Visser, K.P. de Jong, F.M. Mulder, Chem. Eur. J. 9 (2003) 4764], and is in agreement with what is found in first principles calculations [T. Sagara, J. Klassen, E. Ganz, J. Chem. Phys. 121 (2004) 12543; F.M. Mulder, T.J. Dingemans, M. Wagemaker, G.J. Kearley, Chem. Phys. 317 (2005) 113]. Assignments of the INS spectra is realized using comparison with independently published model calculations [F.M. Mulder, T.J. Dingemans, M. Wagemaker, G.J. Kearley, Chem. Phys. 317 (2005) 113] and structural data [T. Yildirim, M.R. Hartman, Phys. Rev. Lett. 95 (2005) 215504].

Selective adsorption of toluene-3,4-dithiol on Si(553)-Au surfaces

NASA Astrophysics Data System (ADS)

Suchkova, Svetlana; Hogan, Conor; Bechstedt, Friedhelm; Speiser, Eugen; Esser, Norbert

2018-01-01

The adsorption of small organic molecules onto vicinal Au-stabilized Si(111) surfaces is shown to be a versatile route towards controlled growth of ordered organic-metal hybrid one-dimensional nanostructures. Density functional theory is used to investigate the site-specific adsorption of toluene-3,4-dithiol (TDT) molecules onto the clean Si(553)-Au surface and onto a co-doped surface whose steps are passivated by hydrogen. We find that the most reactive sites involve bonding to silicon at the step edge or on the terraces, while gold sites are relatively unfavored. H passivation and TDT adsorption both induce a controlled charge redistribution within the surface layer, causing the surface metallicity, electronic structure, and chemical reactivity of individual adsorption sites to be substantially altered.

Metal adsorption on monolayer blue phosphorene: A first principles study

NASA Astrophysics Data System (ADS)

Khan, Imran; Son, Jicheol; Hong, Jisang

2018-01-01

We investigated the electronic structure, adsorption energies, magnetic properties, dipole moment and work function of metal adatoms (Mg, Cr, Mo, Pd, Pt, and Au) adsorption on a blue phosphorene monolayer. For Mg, Pt and Au metals, the most stable state was found in hollow site while for Cr, Mo and Pd metals we found an adsorption in valley site. We suggest that the Pd and Pt atoms prefer 2D growth mode while the Mg, Cr, Mo and Au atoms prefer 3D island growth mode on monolayer phosphorene. The electronic band structures and magnetic properties were dependent on the doping site and dopant materials. For instance, the semiconducting features were preserved in Mg, Pd, Pt, and Au doped systems. However, the Cr and Mo doped systems displayed half-metallic band structures. The total magnetic moment of 4.05, 2.0 and 0.77 μB /impurity atom were obtained in Cr, Mo and Au doped systems whereas the Mg, Pd and Pt doped systems remained nonmagnetic. We also investigated the magnetic interaction between two transition metal impurities. We observed ferromagnetic coupling between two transition metal impurities in Cr and Mo doped systems while the Au doped system displayed almost degenerated magnetic state. For Mg, Cr, and Mo adsorptions, we found relatively large values of dipole moments compared to those in the Pd, Pt and Au adsorptions. This resulted in a significant suppression of the work function in Mg, Cr and Mo adsorptions. Overall, adsorption can tune the physical and magnetic properties of phosphorene monolayer.

Surface complexation modeling of proton and Cd adsorption onto an algal cell wall.

PubMed

Kaulbach, Emily S; Szymanowski, Jennifer E S; Fein, Jeremy B

2005-06-01

This study quantifies Cd adsorption onto the cell wall of the algal species Pseudokirchneriella subcapitata by applying a surface complexation approach to model the observed adsorption behavior. We use potentiometric titrations to determine deprotonation constants and site concentrations for the functional groups on the algal cell wall. Adsorption and desorption kinetics experiments illustrate that adsorption of Cd onto the cell wall is rapid and reversible, except under low pH conditions. Adsorption experiments conducted as a function of pH and total Cd concentration yield the stoichiometry and site-specific stability constants for the important Cd-algal surface complexes. We model the acid/base properties of the algal cell wall by invoking four discrete surface functional group types, with pKa values of 3.9 +/- 0.3, 5.4 +/- 0.1, 7.6 +/- 0.3, and 9.6 +/- 0.4. The results of the Cd adsorption experiments indicate that the first, third, and fourth sites contribute to Cd adsorption under the experimental conditions, with calculated log stability constant values of 4.1 +/- 0.5, 5.4 +/- 0.5, and 6.1 +/- 0.4, respectively. Our results suggest that the stabilities of the Cd-surface complexes are high enough for algal adsorption to affect the fate and transport of Cd under some conditions and that on a per gram basis, algae and bacteria exhibit broadly similar extents of Cd adsorption.

High ionic strength narrows the population of sites participating in protein ion-exchange adsorption: A single-molecule study

PubMed Central

Kisley, Lydia; Chen, Jixin; Mansur, Andrea P.; Dominguez-Medina, Sergio; Kulla, Eliona; Kang, Marci; Shuang, Bo; Kourentzi, Katerina; Poongavanam, Mohan-Vivekanandan; Dhamane, Sagar; Willson, Richard C.; Landes, Christy F.

2014-01-01

The retention and elution of proteins in ion-exchange chromatography is routinely controlled by adjusting the mobile phase salt concentration. It has repeatedly been observed, as judged from adsorption isotherms, that the apparent heterogeneity of adsorption is lower at more-eluting, higher ionic strength. Here, we present an investigation into the mechanism of this phenomenon using a single-molecule, super-resolution imaging technique called motion-blur Points Accumulation for Imaging in Nanoscale Topography (mbPAINT). We observed that the number of functional adsorption sites was smaller at high ionic strength and that these sites had reduced desorption kinetic heterogeneity, and thus narrower predicted elution profiles, for the anion-exchange adsorption of α-lactalbumin on an agarose-supported, clustered-charge ligand stationary phase. Explanations for the narrowing of the functional population such as inter-protein interactions and protein or support structural changes were investigated through kinetic analysis, circular dichroism spectroscopy, and microscopy of agarose microbeads, respectively. The results suggest the reduction of heterogeneity is due to both electrostatic screening between the protein and ligand and tuning the steric availability within the agarose support. Overall, we have shown that single molecule spectroscopy can aid in understanding the influence of ionic strength on the population of functional adsorbent sites participating in the ion-exchange chromatographic separation of proteins. PMID:24751557

The influence of CO adsorption on the surface composition of cobalt/palladium alloys

NASA Astrophysics Data System (ADS)

Murdoch, A.; Trant, A. G.; Gustafson, J.; Jones, T. E.; Noakes, T. C. Q.; Bailey, P.; Baddeley, C. J.

2016-04-01

Segregation induced by the adsorption of gas phase species can strongly influence the composition of bimetallic surfaces and can therefore play an important role in influencing heterogeneous catalytic reactions. The addition of palladium to cobalt catalysts has been shown to promote Fischer Tropsch catalysis. We investigate the adsorption of CO onto bimetallic CoPd surfaces on Pd{111} using a combination of reflection absorption infrared spectroscopy and medium energy ion scattering. The vibrational frequency of adsorbed CO provides crucial information on the adsorption sites adopted by CO and medium energy ion scattering probes the surface composition before and after CO exposure. We show that cobalt segregation is induced by CO adsorption and rationalise these observations in terms of the strength of adsorption of CO in various surface adsorption sites.

Selective sulfur dioxide adsorption on crystal defect sites on an isoreticular metal organic framework series

PubMed Central

Rodríguez-Albelo, L. Marleny; López-Maya, Elena; Hamad, Said; Ruiz-Salvador, A. Rabdel; Calero, Sofia; Navarro, Jorge A.R.

2017-01-01

The widespread emissions of toxic gases from fossil fuel combustion represent major welfare risks. Here we report the improvement of the selective sulfur dioxide capture from flue gas emissions of isoreticular nickel pyrazolate metal organic frameworks through the sequential introduction of missing-linker defects and extra-framework barium cations. The results and feasibility of the defect pore engineering carried out are quantified through a combination of dynamic adsorption experiments, X-ray diffraction, electron microscopy and density functional theory calculations. The increased sulfur dioxide adsorption capacities and energies as well as the sulfur dioxide/carbon dioxide partition coefficients values of defective materials compared to original non-defective ones are related to the missing linkers enhanced pore accessibility and to the specificity of sulfur dioxide interactions with crystal defect sites. The selective sulfur dioxide adsorption on defects indicates the potential of fine-tuning the functional properties of metal organic frameworks through the deliberate creation of defects. PMID:28198376

Isotherms for Water Adsorption on Molecular Sieve 3A: Influence of Cation Composition

DOE PAGES

Lin, Ronghong; Ladshaw, Austin; Nan, Yue; ...

2015-06-16

This study is part of our continuing efforts to address engineering issues related to the removal of tritiated water from off-gases produced in used nuclear fuel reprocessing facilities. In the current study, adsorption equilibrium of water on molecular sieve 3A beads was investigated. Adsorption isotherms for water on the UOP molecular sieve 3A were measured by a continuous-flow adsorption system at 298, 313, 333, and 353 K. Experimental data collected were analyzed by the Generalized Statistical Thermodynamic Adsorption (GSTA) isotherm model. The K +/Na + molar ratio of this particular type of molecular sieve 3A was ~4:6. Our results showedmore » that the GSTA isotherm model worked very well to describe the equilibrium behavior of water adsorption on molecular sieve 3A. The optimum number of parameters for the current experimental data was determined to be a set of four equilibrium parameters. This result suggests that the adsorbent crystals contain four energetically distinct adsorption sites. In addition, it was found that water adsorption on molecular sieve 3A follows a three-stage adsorption process. This three-stage adsorption process confirmed different water adsorption sites in molecular sieve crystals. In addition, the second adsorption stage is significantly affected by the K +/Na + molar ratio. In this stage, the equilibrium adsorption capacity at a given water vapor pressure increases as the K +/Na + molar ratio increases.« less

Adsorption of radionuclides on the monolayer MoS2

NASA Astrophysics Data System (ADS)

Zhao, Qiang; Zhang, Zheng; Ouyang, Xiaoping

2018-04-01

How to remove radionuclides from radioactive wastewater has long been a difficult problem, especially in nuclear accidents. In this paper, the adsorption of radionuclides Cs, Sr, and Ba on the monolayer MoS2 was investigated by using the first principles calculation method. Through the calculation of adsorption energy and Hirshfeld charge of the radionuclides on the monolayer MoS2 at six adsorption sites, the results show that all of the radionuclides chemisorbed on the monolayer MoS2, and the adsorption strength of these three kinds of radionuclides on the monolayer MoS2 is Ba > Sr > Cs. This work might shed some light on the treatment of the radioactive wastewater.

Characteristics of Alcian-blue Dye Adsorption of Natural Biofilm Matrix

NASA Astrophysics Data System (ADS)

Kurniawan, A.; Yamamoto, T.; Sukandar; Guntur

2018-01-01

In this study, natural biofilm matrices formed on stones have been used for the adsorption of Alcian blue dye. Alcian blue is a member of polyvalent basic dyes that largely used from laboratory until industrial dying purposes. The adsorption of the dye onto the biofilm matrix has been carried out at different experimental conditions such as adsorption isotherm and kinetic of adsorption. The electric charge properties of biofilm matrix and its changes related to the adsorption of Alcian blue have been also investigated. Moreover, the results of Alcian blue adsorption to the biofilm were compared to those onto the acidic and neutral resin. The kinetics of adsorption result showed that the adsorption of the Alcian blue dye reached to a maximum adsorption amount within 60 minutes. The adsorption amount of Alcian blue to biofilm increased monotonously, and the maximum adsorption amount was greater compared to the resins. On the contrary, Alcian blue did not attach to the neutral resin having no electric charge. It seems that Alcian blue attached to the acidic resins due to electrostatic attractive force, and the same seems to be the case for adsorption of Alcian blue to biofilm. The adsorption of Alcian blue to the biofilm and acidic resins fitted to Langmuir type indicates that the binding of Alcian blue to the biofilm and acidic resins occurred in a monolayer like form. The maximum adsorption amount of Alcian blue on the biofilm (0.24 mmol/dry-g) was greater than those of acidic resin (0.025 mmol/dry-g). This indicates that the biofilm has many more sites for Alcian blue attachment than acidic resins. According to the result of this study, the biofilm matrix can be a good adsorbent for dye such as Alcian blue or other dyes that causing hazards in nature.

Preparation and evaluation of molecularly imprinted polymer for selective recognition and adsorption of gossypol.

PubMed

Zhi, Keke; Wang, Lulu; Zhang, Yagang; Zhang, Xuemin; Zhang, Letao; Liu, Li; Yao, Jun; Xiang, Wei

2018-03-01

Molecularly imprinted polymers (MIPs) were designed and prepared via bulk thermal polymerization with gossypol as the template molecule and dimethylaminoethyl methacrylate as the functional monomer. The morphology and microstructures of MIPs were characterized by scanning electron microscope and Brunauer-Emmett-Teller surface areas. Static adsorption tests were performed to evaluate adsorption behavior of gossypol by the MIPs. It was found that adsorption kinetics and adsorption isotherms data of MIPs for gossypol were fit well with the pseudo-second-order model and Freundlich model, respectively. Scatchard analysis showed that heterogeneous binding sites were formed in the MIPs, including lower-affinity binding sites with the maximum adsorption of 252 mg/g and higher-affinity binding sites with the maximum adsorption of 632 mg/g. Binding studies also revealed that MIPs had favorable selectivity towards gossypol compared with non-imprinted polymers. Furthermore, adsorption capacity of MIPs maintained above 90% after 5 regeneration cycles, indicating MIPs were recyclable and could be used multiple times. These results demonstrated that prepared MIPs could be a promising functional material for selective adsorption of gossypol. Copyright © 2017 John Wiley & Sons, Ltd.

Adsorption kinetics of surfactants on activated carbon

NASA Astrophysics Data System (ADS)

Arnelli; Aditama, WP; Fikriani, Z.; Astuti, Y.

2018-04-01

A study on the adsorption of both cationic and anionic surfactants using activated carbon as well as the investigation of the adsorption isotherms and adsorption kinetics has been conducted. The results showed that the adsorption of sodium lauryl sulfate (SLS) by activated carbon was Langmuir’s adsorption isotherm while its adsorption kinetics showed pseudo-second order with an adsorption rate constant of 2.23 x 103 g mg-1 hour-1. Meanwhile, the adsorption of HDTMA-Br by activated carbon showed that the isotherm adsorption tended to follow Freundlich’s isotherm and was pseudo-second order with an adsorption rate constant of 89.39 g mg-1 hour-1.

Study of adsorption of Neon on open Carbon nanohorns aggregates

NASA Astrophysics Data System (ADS)

Ziegler, Carl Andrew

Adsorption isotherms can be used to determine surface area of a substrate and the heat released when adsorption occurs. Our measurements are done determining the equilibrium pressures corresponding to a given amount of gas adsorbed on a substrate at constant temperature. The adsorption studies were done on aggregates of open dahlia-like carbon nanohorns. The nanohorns were oxidized for 9 hours at 550 °C to open them up and render their interior space accessible for adsorption. Volumetric adsorption measurements of Ne were performed at twelve different temperatures between 19 K and 48 K. The isotherms showed two substeps. The first substep corresponds to adsorption on the high energy binding sites in the interior of the nanohorns, near the tip. The second substep corresponds to low energy binding sites both on the outside of the nanotubes and inside the nanotube away from the tip. The isosteric heat measurements obtained from the isotherm data also shows these two distinct substeps. The effective surface area of the open nanotubes was determined from the isotherms using the point-B method. The isosteric heat and surface area data for neon on open nanohorns were compared to two similar experiments of neon adsorbed on aggregates of closed nanohorns.

Ab initio molecular dynamics determination of competitive O₂ vs. N₂ adsorption at open metal sites of M₂(dobdc).

PubMed

Parkes, Marie V; Greathouse, Jeffery A; Hart, David B; Gallis, Dorina F Sava; Nenoff, Tina M

2016-04-28

The separation of oxygen from nitrogen using metal-organic frameworks (MOFs) is of great interest for potential pressure-swing adsorption processes for the generation of purified O2 on industrial scales. This study uses ab initio molecular dynamics (AIMD) simulations to examine for the first time the pure-gas and competitive gas adsorption of O2 and N2 in the M2(dobdc) (M = Cr, Mn, Fe) MOF series with coordinatively unsaturated metal centers. Effects of metal, temperature, and gas composition are explored. This unique application of AIMD allows us to study in detail the adsorption/desorption processes and to visualize the process of multiple guests competitively binding to coordinatively unsaturated metal sites of a MOF.

Adsorption and Gas Separation of Molecules by Carbon Nanohorns.

PubMed

Gatica, Silvina M; Nekhai, Anton; Scrivener, Adam

2016-05-19

In this paper, we report the results of Monte Carlo simulations of the adsorption of neon, argon, methane and carbon dioxide in carbon nanohorns. We model the nanohorns as an array of carbon cones and obtained adsorption isotherms and isosteric heats. The main sites of adsorption are inside the cones and in the interstices between three cones. We also calculated the selectivity of carbon dioxide/methane, finding that nanohorns are a suitable substrate for gas separation. Our simulations are compared to available experimental data.

Adsorption of SO2 on bituminous coal char and activated carbon fiber

USGS Publications Warehouse

DeBarr, Joseph A.; Lizzio, Anthony A.; Daley, Michael A.

1997-01-01

The SO2 adsorption behaviors of activated carbons produced from Illinois coal and of commercially prepared activated carbon fibers (ACFs) were compared. There was no relation between surface area of coal-based carbons and SO2 adsorption, whereas adsorption of SO2 on the series of ACFs was inversely proportional to N2 BET surface area. Higher surface area ACFs had wider pores and adsorbed less SO2; thus, pore size distribution is thought to play a significant role in SO2 adsorption for these materials. Oxidation with HNO3 and/or H2SO4, followed by heat treatment at 700−925°C to remove carbon−oxygen complexes, resulted in increased SO2 adsorption for both coal chars and ACFs. This behavior was explained by an increase in the available number of free sites, previously occupied by oxygen and now available for SO2 adsorption. The use of nitrogen-containing functional groups on ACFs of proper pore size shows promise for further increasing SO2 adsorption capacities. Knowledge of the relationship among the number of free sites, pore size, and surface chemistry on corresponding SO2 adsorption should lead to the development of more efficient adsorbents prepared from either coal or ACFs.

Goethite surface reactivity: a macroscopic investigation unifying proton, chromate, carbonate, and lead(II) adsorption.

PubMed

Villalobos, Mario; Pérez-Gallegos, Ayax

2008-10-15

The goethite surface structure has been extensively studied, but no convincing quantitative description of its highly variable surface reactivity as inversely related to its specific surface area (SSA) has been found. The present study adds experimental evidence and provides a unified macroscopic explanation to this anomalous behavior from differences in average adsorption capacities, and not in average adsorption affinities. We investigated the chromate anion and lead(II) cation adsorption behavior onto three different goethites with SSA varying from 50 to 94 m(2)/g, and analyzed an extensive set of published anion adsorption and proton charging data for variable SSA goethites. Maximum chromate adsorption was found to occupy on average from 3.1 to 9.7 sites/nm(2), inversely related to SSA. Congruency of oxyanion and Pb(II) adsorption behavior based on fractional site occupancy using these values, and a site density analysis suggest that: (i) ion binding occurs to singly and doubly coordinated sites, (ii) proton binding occurs to singly and triply coordinated sites (ranging from 6.2 to 8 total sites/nm(2), in most cases), and (iii) a predominance of (210) and/or (010) faces explains the high reactivity of low SSA goethites. The results imply that the macroscopic goethite adsorption behavior may be predicted without a need to investigate extensive structural details of each specific goethite of interest.

Predicting Multicomponent Adsorption Isotherms in Open-Metal Site Materials Using Force Field Calculations Based on Energy Decomposed Density Functional Theory.

PubMed

Heinen, Jurn; Burtch, Nicholas C; Walton, Krista S; Fonseca Guerra, Célia; Dubbeldam, David

2016-12-12

For the design of adsorptive-separation units, knowledge is required of the multicomponent adsorption behavior. Ideal adsorbed solution theory (IAST) breaks down for olefin adsorption in open-metal site (OMS) materials due to non-ideal donor-acceptor interactions. Using a density-function-theory-based energy decomposition scheme, we develop a physically justifiable classical force field that incorporates the missing orbital interactions using an appropriate functional form. Our first-principles derived force field shows greatly improved quantitative agreement with the inflection points, initial uptake, saturation capacity, and enthalpies of adsorption obtained from our in-house adsorption experiments. While IAST fails to make accurate predictions, our improved force field model is able to correctly predict the multicomponent behavior. Our approach is also transferable to other OMS structures, allowing the accurate study of their separation performances for olefins/paraffins and further mixtures involving complex donor-acceptor interactions. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Kinetics of Cation and Oxyanion Adsorption and Desorption on Ferrihydrite: Roles of Ferrihydrite Binding Sites and a Unified Model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tian, Lei; Shi, Zhenqing; Lu, Yang

Understanding the kinetics of toxic ion reactions with ferrihydrite is crucial for predicting the dynamic behavior of contaminants in soil environments. In this study, the kinetics of As(V), Cr(VI), Cu, and Pb adsorption and desorption on ferrihydrite were investigated with a combination of laboratory macroscopic experiments, microscopic investigation and mechanistic modeling. The rates of As(V), Cr(VI), Cu, and Pb adsorption and desorption on ferrihydrite, as systematically studied using a stirred-flow method, was highly dependent on the reaction pH and metal concentrations and varied significantly among four metals. Spherical aberration-corrected scanning transmission electron microscopy (Cs-STEM) showed, at sub-nano scales, all fourmore » metals were distributed within the ferrihydrite particle aggregates homogeneously after adsorption reactions, with no evidence of surface diffusion-controlled processes. Based on experimental results, we developed a unifying kinetics model for both cation and oxyanion adsorption/desorption on ferrihydrite based on the mechanistic-based equilibrium model CD-MUSIC. Overall, the model described the kinetic results well, and we quantitatively demonstrated how the equilibrium properties of the cation and oxyanion binding to various ferrihydrite sites affected the adsorption and desorption rates. Our results provided a unifying quantitative modeling method for the kinetics of both cation and oxyanion adsorption/desorption on iron minerals.« less

Crystal Face Distributions and Surface Site Densities of Two Synthetic Goethites: Implications for Adsorption Capacities as a Function of Particle Size.

PubMed

Livi, Kenneth J T; Villalobos, Mario; Leary, Rowan; Varela, Maria; Barnard, Jon; Villacís-García, Milton; Zanella, Rodolfo; Goodridge, Anna; Midgley, Paul

2017-09-12

Two synthetic goethites of varying crystal size distributions were analyzed by BET, conventional TEM, cryo-TEM, atomic resolution STEM and HRTEM, and electron tomography in order to determine the effects of crystal size, shape, and atomic scale surface roughness on their adsorption capacities. The two samples were determined by BET to have very different site densities based on Cr VI adsorption experiments. Model specific surface areas generated from TEM observations showed that, based on size and shape, there should be little difference in their adsorption capacities. Electron tomography revealed that both samples crystallized with an asymmetric {101} tablet habit. STEM and HRTEM images showed a significant increase in atomic-scale surface roughness of the larger goethite. This difference in roughness was quantified based on measurements of relative abundances of crystal faces {101} and {201} for the two goethites, and a reactive surface site density was calculated for each goethite. Singly coordinated sites on face {210} are 2.5 more dense than on face {101}, and the larger goethite showed an average total of 36% {210} as compared to 14% for the smaller goethite. This difference explains the considerably larger adsorption capacitiy of the larger goethite vs the smaller sample and points toward the necessity of knowing the atomic scale surface structure in predicting mineral adsorption processes.

Effects of NH4+, K+, Mg2+, and Ca2+ on the Cesium Adsorption/Desorption in Binding Sites of Vermiculitized Biotite.

PubMed

Yin, Xiangbiao; Wang, Xinpeng; Wu, Hao; Takahashi, Hideharu; Inaba, Yusuke; Ohnuki, Toshihiko; Takeshita, Kenji

2017-12-05

The reversibility of cesium adsorption in contaminated soil is largely dependent on its interaction with micaceous minerals, which may be greatly influenced by various cations. Herein, we systematically investigated the effects of NH 4 + , K + , Mg 2+ , and Ca 2+ on the adsorption/desorption of Cs + into different binding sites of vermiculitized biotite (VB). Original VB was initially saturated by NH 4 + , K + , or Mg 2+ ; we then evaluated the adsorption of Cs + on three treated VBs, and the desorption by extraction with NH 4 + , K + , Mg 2+ , or Ca 2+ was further evaluated. Our structural analysis and Cs + extractability determinations showed that NH 4 + and K + both collapsed the interlayers of VB, resulting in the dominant adsorption of Cs + to external surface sites on which Cs + was readily extracted by NH 4 + , K + , Mg 2+ , or Ca 2+ irrespective of their species, whereas Mg 2+ maintained the VB with expanded interlayers, leading to the overwhelming adsorption of Cs + in collapsed interlayer sites on which the Cs + desorption was difficult and varied significantly by the cations used in extraction. The order of Cs + extraction ability from the collapsed interlayers was K + ≫ Mg 2+ ≈ Ca 2+ ≫ NH 4 + . These results could provide important insights into Cs migration in soil and its decontamination for soil remediation.

A quantum chemical study for exploring the inhibitory effect of nitrogen containing species on the adsorption of polynuclear aromatic hydrocarbons over a Bronsted acid site

NASA Astrophysics Data System (ADS)

Celis-Cornejo, C. M.; Garnica Mantilla, M. M.; Baldovino-Medrano, V. G.; Ramírez-Caballero, G. E.

2016-08-01

The analysis of the inhibitory effect of nitrogenated compounds on the hydroprocessing and hydropurification of oil derived fuels is important to produce cleaner fuels. In this work, density functional theory calculations were performed to investigate the effect of the nitrogen containing molecules on the adsorption of Polynuclear Aromatic Hydrocarbons (PAHs). Mordenite was chosen as a zeolitic structure for simulating a Bronsted acid site. The character of the acid site was confirmed by both a vibrational frequency calculation and a Bader charge analysis. From the adsorption calculations, it was found that the adsorption energy of PAHs increases with the number of aromatic rings in the structure. Also, the nitrogen containing species possibly inhibit more extensively two and three rings PAHs because of their lower adsorption energies. Finally, it was observed that the nitrogen species tend to drag the proton from the mordenite acid site. This explains the inhibitory effect in the adsorption of PAHs and contributes to understanding the dynamics of hydrocarbon hydroprocessing in refineries.

Adsorption properties of AlN on Si(111) surface: A density functional study

NASA Astrophysics Data System (ADS)

Yuan, Yinmei; Zuo, Ran; Mao, Keke; Tang, Binlong; Zhang, Zhou; Liu, Jun; Zhong, Tingting

2018-04-01

In the process of preparing GaN on Si substrate by MOCVD, an AlN buffer layer is very important. In this study, we conducted density functional theory calculations on the adsorption of AlN molecule on Si(111)-(2 × 2) surface, with the AlN molecule located horizontally or vertically above Si(111) surface at different adsorption sites. The calculations revealed that the lowest adsorption energy was at the N-top-Al-bridge site in the horizontal configuration, with the narrowest band gap, indicating that it was the most preferential adsorption growth status of AlN. In the vertical configurations, N adatom was more reactive and convenient to form bonds with the topmost Si atoms than Al adatom. When the N-end of the AlN molecule was located downward, the hollow site was the preferred adsorption site; when the Al-end was located downward, the bridge site was the most energetically favorable. Moreover, we investigated some electronic properties such as partial density of states, electron density difference, Mulliken populations, etc., revealing the microscale mechanism for AlN adsorption on Si(111) surface and providing theoretical support for adjusting the processing parameters during AlN or GaN production.

Cysteine and cystine adsorption on FeS2(100)

NASA Astrophysics Data System (ADS)

Suzuki, Teppei; Yano, Taka-aki; Hara, Masahiko; Ebisuzaki, Toshikazu

2018-08-01

Iron pyrite (FeS2) is the most abundant metal sulfide on Earth. Owing to its reactivity and catalytic activity, pyrite has been studied in various research fields such as surface science, geochemistry, and prebiotic chemistry. Importantly, native iron-sulfur clusters are typically coordinated by cysteinyl ligands of iron-sulfur proteins. In the present paper, we study the adsorption of L-cysteine and its oxidized dimer, L-cystine, on the FeS2 surface, using electronic structure calculations based density functional theory and Raman spectroscopy measurements. Our calculations suggest that sulfur-deficient surfaces play an important role in the adsorption of cysteine and cystine. In the thiol headgroup adsorption on the sulfur-vacancy site, dissociative adsorption is found to be energetically favorable compared with molecular adsorption. In addition, the calculations indicate that, in the cystine adsorption on the defective surface under vacuum conditions, the formation of the S-Fe bond is energetically favorable compared with molecular adsorption. Raman spectroscopic measurements suggest the formation of cystine molecules through the S-S bond on the pyrite surface in aqueous solution. Our results might have implications for chemical evolution at mineral surfaces on the early Earth and the origin of iron-sulfur proteins, which are believed to be one of the most ancient families of proteins.

Role of adsorption in liquid lubrication

NASA Technical Reports Server (NTRS)

Groszek, A. J.

1973-01-01

Changes at solid-liquid interfaces caused by adsorption from solution are discussed paying attention to the following aspects: (1) stability of adsorbed films and the structure of metal-additive-film-liquid interface and effect of adsorbate orientation. (2) chemical versus physical adsorption, (3) heat of adsorption, (4) adsorption of additives, (5) activated adsorption, effect of activating adsorbates, (6) displacement phenomena at solid-liquid interfaces, (7) competition of antiwear additives, their solvents, and water, (8) effect of adsorption on the orientation of liquid in the interfacial region, and (9) relation between the chemical nature of solid surfaces and their interaction with liquid lubricants. The relevance of the above adsorption phenomena to lubrication is discussed, referring where possible to specific examples.

How strong is the edge effect in the adsorption of anticancer drugs on a graphene cluster?

PubMed

Rungnim, Chompoonut; Chanajaree, Rungroj; Rungrotmongkol, Thanyada; Hannongbua, Supot; Kungwan, Nawee; Wolschann, Peter; Karpfen, Alfred; Parasuk, Vudhichai

2016-04-01

The adsorption of nucleobase-analog anticancer drugs (fluorouracil, thioguanine, and mercaptopurine) on a graphene flake (C54H18) was investigated by shifting the site at which adsorption occurs from one end of the sheet to the other end. The counterpoise-corrected M06-2X/cc-pVDZ binding energies revealed that the binding stability decreases in the sequence thioguanine > mercaptopurine > fluorouracil. We found that adsorption near the middle of the sheet is more favorable than adsorption near the edge due to the edge effect. This edge effect is stronger for the adsorption of thioguanine or mercaptopurine than for fluorouracil adsorption. However, the edge effect reduces the binding energy of the drug to the flake by only a small amount, <5 kcal/mol, depending on the adsorption site and the alignment of the drug at this site.

ARSENIC TREATMENT BY ADSORPTIVE TECHNOLOGY

EPA Science Inventory

Presentation will discuss the removal of arsenic from drinking water using the adsorptive media treatment process. Fundamental information is provided on the design and operation of adsorptive media technology including the selection of the adsorptive media. The information cites...

Method and apparatus for thermal swing adsorption and thermally-enhanced pressure swing adsorption

DOEpatents

Wegeng, Robert S.; Rassat, Scot D.; TeGrotenhuis, Ward E.; Drost, Kevin; Vishwanathan, Vilayanur V.

2004-06-08

The present invention provides compact adsorption systems that are capable of rapid temperature swings and rapid cycling. Novel methods of thermal swing adsorption and thermally-enhanced pressure swing adsorption are also described. In some aspects of the invention, a gas is passed through the adsorbent thus allowing heat exchangers to be very close to all portions of the adsorbent and utilize less space. In another aspect, the adsorption media is selectively heated, thus reducing energy costs. Methods and systems for gas adsorption/desorption having improved energy efficiency with capability of short cycle times are also described. In another aspect, the apparatus or methods utilize heat exchange channels of varying lengths that have volumes controlled to provide equal heat fluxes. Methods of fuel cell startup are also described. Advantages of the invention include the ability to use (typically) 30-100 times less adsorbent compared to conventional systems.

[Adsorption kinetics and mechanism of lead (II) on polyamine-functionalized mesoporous activated carbon].

PubMed

Li, Kun-Quan; Wang, Yan-Jin; Yang, Mei-Rong; Zhu, Zhi-Qiang; Zheng, Zheng

2014-08-01

Bagasse mesoporous carbon was prepared by microwave assisted H3 PO4 activation. Amido and imido groups were modified with ethanediamine on the channels' surface of mesoporous carbon through nitric oxidation and amide reaction. The influence of Pb(II) concentration, adsorption time on Pb(II) adsorption on the ethanediamine-modified mesoporous carbon (AC-EDA) was investigated. The adsorption kinetics and mechanism were also discussed. The results showed that AC-EDA had a great performance for Pb(II) adsorption, and more than 70% of Pb(II) was adsorbed in 5 minutes. The adsorption amount of Pb(II) on the carbon increased with the increase of solution pH in acidic conditions. It was found that AC-EDA had different binding energies on different adsorption sites for Pb(II) separation. The Pb(II) adsorption process on AC-EDA was controlled by intra-particle diffusion in the first 3 min, and then film diffusion played the important pole on the adsorption. The adsorption amount increased with the increase of temperature, indicating the adsorption was an endothermic reaction. The high adsorption energy (> 11 kJ x mol(-1)) implied that the) adsorption was a chemical adsorption. The XPS of AC-EDA before and after Pb(II) adsorption showed that the polyamine group was involved in the adsorption, and should be a main factor of the high efficient adsorption.

Periodic DFT study of acidic trace atmospheric gas molecule adsorption on Ca- and Fe-doped MgO(001) surface basic sites.

PubMed

Baltrusaitis, Jonas; Hatch, Courtney; Orlando, Roberto

2012-08-02

The electronic properties of undoped and Ca- or Fe-doped MgO(001) surfaces, as well as their propensity toward atmospheric acidic gas (CO2, SO2, and NO2) uptake was investigated with an emphasis on gas adsorption on the basic MgO oxygen surface sites, O(surf), using periodic density functional theory (DFT) calculations. Adsorption energy calculations show that MgO doping will provide stronger interactions of the adsorbate with the O(surf) sites than the undoped MgO for a given adsorbate molecule. Charge transfer from the iron atom in Fe-doped MgO(001) to NO2 was shown to increase the binding interaction between adsorbate by an order of magnitude, when compared to that of undoped and Ca-doped MgO(001) surfaces. Secondary binding interactions of adsorbate oxygen atoms were observed with surface magnesium sites at distances close to those of the Mg-O bond within the crystal. These interactions may serve as a preliminary step for adsorption and facilitate further adsorbate transformations into other binding configurations. Impacts on global atmospheric chemistry are discussed as these adsorption phenomena can affect atmospheric gas budgets via altered partitioning and retention on mineral aerosol surfaces.

Periodic DFT study of acidic trace atmospheric gas molecule adsorption on Ca and Fe doped MgO (001) surface basic sites

PubMed Central

Hatch, Courtney; Orlando, Roberto

2012-01-01

The electronic properties of undoped and Ca or Fe doped MgO (001) surfaces, as well as their propensity towards atmospheric acidic gas (CO2, SO2 and NO2) uptake was investigated with an emphasis on gas adsorption on the basic MgO oxygen surface sites, Osurf, using periodic Density Functional Theory (DFT) calculations. Adsorption energy calculations show that MgO doping will provide stronger interactions of the adsorbate with the Osurf sites than the undoped MgO for a given adsorbate molecule. Charge transfer from the iron atom in Fe doped MgO (001) to NO2 was shown to increase the binding interaction between adsorbate by an order of magnitude, when compared to that of undoped and Ca doped MgO (001) surfaces. Secondary binding interactions of adsorbate oxygen atoms were observed with surface magnesium sites at distances close to those of the Mg-O bond within the crystal. These interactions may serve as a preliminary step for adsorption and facilitate further adsorbate transformations into other binding configurations. Impacts on global atmospheric chemistry are discussed as these adsorption phenomena can affect atmospheric gas budgets via altered partitioning and retention on mineral aerosol surfaces. PMID:22775293

Adsorption of organic chemicals in soils.

PubMed Central

Calvet, R

1989-01-01

This paper presents a review on adsorption of organic chemicals on soils sediments and their constituents. The first part of this review deals with adsorption from gas and liquid phases and gives a discussion on the physical meaning of the shape of adsorption isotherms. Results show that no general rules can be proposed to describe univocally the relation between the shape of isotherms and the nature of adsorbate-adsorbent system. Kinetics of adsorption is discussed through the description of various models. Theoretical developments exist both for the thermodynamics and the kinetics of adsorption, but there is a strong need for experimental results. Possible adsorption mechanisms are ion exchange, interaction with metallic cations, hydrogen bonds, charge transfers, and London-van der Waals dispersion forces/hydrophobic effect. However, direct proofs of a given mechanism are rare. Several factors influence adsorption behavior. Electronic structure of adsorbed molecules, properties of adsorbents, and characteristics of the liquid phase are discussed in relation to adsorption. Such properties as water solubility, organic carbon content of adsorbing materials, and the composition of the liquid phase are particularly important. Evaluation of adsorption can be obtained through either laboratory measurements or use of several correlations. Adsorption measurements must be interpreted, taking into account treatment of adsorbent materials, experimental conditions, and secondary phenomena such as degradations. Correlations between adsorption coefficients and water-octanol partition coefficient or water solubility are numerous. They may be useful tools for prediction purposes. Relations with transport, bioavailability, and degradation are described. PMID:2695323

Adsorption of p-nitrophenols (PNP) on microalgal biochar: Analysis of high adsorption capacity and mechanism.

PubMed

Zheng, Heshan; Guo, Wanqian; Li, Shuo; Chen, Yidi; Wu, Qinglian; Feng, Xiaochi; Yin, Renli; Ho, Shih-Hsin; Ren, Nanqi; Chang, Jo-Shu

2017-11-01

Biochars derived from three microalgal strains (namely, Chlorella sp. Cha-01, Chlamydomonas sp. Tai-03 and Coelastrum sp. Pte-15) were evaluated for their capacity to adsorb p-nitrophenols (PNP) using raw microalgal biomass and powdered activated carbon (PAC) as the control. The results show that BC-Cha-01 (biochar from Chlorella sp. Cha-01) exhibited a high PNP adsorption capacity of 204.8mgg -1 , which is 250% and 140% higher than that of its raw biomass and PAC, respectively. The adsorption kinetics and equilibrium are well described with pseudo-second-order equation and Freundlich model, respectively. BC-Cha-01 was found to contain higher polarity moieties with more O-containing functional groups than PAC and other microalgae-derived biochars. The strong polarity of binding sites on BC-Cha-01 may be responsible for its superior adsorption capacity. The biochars from Chlorella sp. Cha-01 seem to have the potential to serve as a highly efficient PNP adsorbent for wastewater treatment or emergency water pollution control. Copyright © 2017 Elsevier Ltd. All rights reserved.

The adsorption of argon on ZnO at 77K

NASA Astrophysics Data System (ADS)

Marinelli, Francis; Grillet, Yves; Pellenq, Roland J.-M.

We have studied the adsorption of argon onto ZnO surfaces at 77K by means of quasiequilibrium adsorption volumetry coupled with high resolution microcalorimetry and Grand Canonical Monte-Carlo (GCMC) simulations. The adsorbate/surface adsorption potential function (PN type) used in the simulations, was determined on the basis of ab initio calculations (corrected for dispersion interactions). The first aspect of this work was to test the ability of a standard solid-state Hartree-Fock technique coupled with a perturbative semiempirical approach in deriving a reliable adsorption potential function. The dispersion part of the adsorbate/surface interatomic potential was derived by using perturbation theory-based equations while the repulsive and induction interactions were derived from periodic HartreeFock (CRYSTAL92) calculations. GCMC simulations based on this adsorption potential allow one to calculate adsorption isotherms and isosteric heat versus loading curves as well as singlet distribution functions at 77K for each type of ZnO (neutral and polar) faces. The combined analysis of the simulation data for all surfaces gives a good insight of the adsorption mechanism of argon onto ZnO surfaces at 77K in agreement with experiment. As far as neutral surfaces are concerned, it is shown that adsorption first takes place within the 'troughs' which cover ZnO neutral surfaces. At low chemical potentials, these semi-channels are preferential adsorption sites in which we could detect a nearly one-dimensional adsorbate freezing in a commensurate phase at 77K. The polar O faces are the most favourable surfaces for adsorption at higher chemical potentials.

Doping and vacancy effects of graphyne on SO2 adsorption.

PubMed

Kim, Sunkyung; Lee, Jin Yong

2017-05-01

The adsorption of sulfur dioxide (SO 2 ) on pristine and modified graphyne (including boron- or nitrogen- doping and introducing a single carbon atom defect) was investigated by density functional theory calculations. The structural, electronic, and magnetic properties of graphyne were changed according to the dopant atom site of doping and vacancy. SO 2 adsorption was obviously affected by modification of graphyne. SO 2 weakly interacted with pristine and nitrogen-doped graphynes. Boron doping at the sp-hybridized carbon site and introducing a single carbon atom vacancy in graphyne brought about a dramatic enhancement in SO 2 adsorption. The strongly chemisorbed SO 2 at these active sites caused deformation of the graphyne structure and electron redistribution, which induced changes in the conductivity and magnetism of graphynes. Copyright © 2017 Elsevier Inc. All rights reserved.

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.

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.

Reactive adsorption of SO2 on activated carbons with deposited iron nanoparticles.

PubMed

Arcibar-Orozco, Javier A; Rangel-Mendez, J Rene; Bandosz, Teresa J

2013-02-15

The effect of iron particle size anchored on the surface of commercial activated carbon on the removal of SO(2) from a gas phase was studied. Nanosize iron particles were deposited using forced hydrolysis of FeCl(3) with or without H(3)PO(4) as a capping agent. Dynamic adsorption experiments were carried out on either dry or pre-humidified materials and the adsorption capacities were calculated. The surface of the initial and exhausted materials was extensively characterized by microscopic, porosity, thermogravimetric and surface chemistry. The results indicate that the SO(2) adsorption capacity increased two and half times after the prehumidification process owing to the formation of H(2)SO(4) in the porous system. Iron species enhance the SO(2) adsorption capacity only when very small nanoparticles are deposited on the pore walls as a thin layer. Large iron nanoparticles block the ultramicropores decreasing the accessibility of the active sites and consuming oxygen that rest adsorption centers for SO(2) molecules. Iron nanoparticles of about 3-4 nm provide highly dispersed adsorption sites for SO(2) molecules and thus increase the adsorption capacity of about 80%. Fe(2)(SO(4))(3) was detected on the surface of exhausted samples. Copyright © 2012 Elsevier B.V. All rights reserved.

Probing Gas Adsorption in Zeolites by Variable-Temperature IR Spectroscopy: An Overview of Current Research.

PubMed

Garrone, Edoardo; Delgado, Montserrat R; Bonelli, Barbara; Arean, Carlos O

2017-09-15

The current state of the art in the application of variable-temperature IR (VTIR) spectroscopy to the study of (i) adsorption sites in zeolites, including dual cation sites; (ii) the structure of adsorption complexes and (iii) gas-solid interaction energy is reviewed. The main focus is placed on the potential use of zeolites for gas separation, purification and transport, but possible extension to the field of heterogeneous catalysis is also envisaged. A critical comparison with classical IR spectroscopy and adsorption calorimetry shows that the main merits of VTIR spectroscopy are (i) its ability to provide simultaneously the spectroscopic signature of the adsorption complex and the standard enthalpy change involved in the adsorption process; and (ii) the enhanced potential of VTIR to be site specific in favorable cases.

Adsorption of multi-heavy metals Zn and Cu onto surficial sediments: modeling and adsorption capacity analysis.

PubMed

Li, Shanshan; Zhang, Chen; Wang, Meng; Li, Yu

2014-01-01

Improved multiple regression adsorption models (IMRAMs) was developed to estimate the adsorption capacity of the components [Fe oxides (Fe), Mn oxides (Mn), organic materials (OMs), residuals] in surficial sediments for multi-heavy metal Zn and Cu. IMRAM is an improved version over MRAM, which introduces a computer program in the model developing process. As MRAM, Zn(Cu) IMRAM, and Cu(Zn) IMRAM again confirmed that there is significant interaction effects that control the adsorption of compounded Zn and Cu, which was neglected by additional adsorption model. The verification experiment shows that the relative deviation of the IMRAMs is less than 13%. It is revealed by the IMRAMs that Mn, which has the greatest adsorption capability for compounded Zn and Cu (54.889 and 161.180 mg/l, respectively), follows by interference adsorption capacity of Fe/Mn (-1.072 and -24.591 mg/l respectively). Zn and Cu influence each other through different mechanisms. When Zn is the adsorbate, compounded Cu mainly affects the adsorption capacities of Fe/Mn and Fe/Mn/OMs; while when Cu is the adsorbate, compounded Zn mainly exerts its effect on Mn, Fe/Mn, and Mn/OMs. It also shows that the compounded Zn or Cu weakened the interference adsorption of Fe/Mn, and meanwhile, strengthened the interference adsorption of Mn/OMs.

Surface Complexation Modeling of Fluoride Adsorption by Soil and the Role of Dissolved Aluminum on Adsorption

NASA Astrophysics Data System (ADS)

Padhi, S.; Tokunaga, T.

2017-12-01

Adsorption of fluoride (F) on soil can control the mobility of F and subsequent contamination of groundwater. Hence, accurate evaluation of adsorption equilibrium is a prerequisite for understanding transport and fate of F in the subsurface. While there have been studies for the adsorption behavior of F with respect to single mineral constituents based on surface complexation models (SCM), F adsorption to natural soil in the presence of complexing agents needs much investigation. We evaluated the adsorption processes of F on a natural granitic soil from Tsukuba, Japan, as a function of initial F concentration, ionic strength, and initial pH. A SCM was developed to model F adsorption behavior. Four possible surface complexation reactions were postulated with and without including dissolved aluminum (Al) and Al-F complex sorption. Decrease in F adsorption with the increase in initial pH was observed in between the initial pH range of 4 to 9, and a decrease in the rate of the reduction of adsorbed F with respect to the increase in the initial pH was observed in the initial pH range of 5 to 7. Ionic strength variation in the range of 0 to 100mM had insignificant effect on F removal. Changes in solution pH were observed by comparing the solution before and after F adsorption experiments. At acidic pH, the solution pH increased, whereas at alkaline pH, the solution pH decreased after equilibrium. The SCM including dissolved Al and the adsorption of Al-F complex can simulate the experimental results quite successfully. Also, including dissolved Al and the adsorption of Al-F complex to the model explained the change in solution pH after F adsorption.

Adsorption in single-walled carbon nanotubes by experiments and molecular simulation II: Effect of morphology and temperature on organic adsorption

USGS Publications Warehouse

Agnihotri, S.; Rostam-Abadi, M.; Mota, J.P.B.; Rood, M.J.

2005-01-01

Hexane adsorption on single-walled carbon nanotube (SWNT) bundles was studied. Hexane adsorption capacities of two purified SWNT samples was gravimetrically determined at isothermal conditions of 25??, 37??, and 50??C for 10-4 < p/po < 0.9, where p/po is hexane vapor pressure relative to its saturation pressure. Simulation of hexane adsorption under similar temperature and pressure conditions were performed on the external and internal sites of nanotube bundles of diameters same as those in experimental samples. The simulations could predict isotherms for a hypothetical scenario where all nanotubes in a sample would be open. This is an abstract of a paper presented at the AIChE Annual Meeting and Fall Showcase (Cincinnati, OH 10/30/2005-11/4/2005).

Perchlorate adsorption and desorption on activated carbon and anion exchange resin.

PubMed

Yoon, In-Ho; Meng, Xiaoguang; Wang, Chao; Kim, Kyoung-Woong; Bang, Sunbaek; Choe, Eunyoung; Lippincott, Lee

2009-05-15

The mechanisms of perchlorate adsorption on activated carbon (AC) and anion exchange resin (SR-7 resin) were investigated using Raman, FTIR, and zeta potential analyses. Batch adsorption and desorption results demonstrated that the adsorption of perchlorate by AC and SR-7 resin was reversible. The reversibility of perchlorate adsorption by the resin was also proved by column regeneration test. Solution pH significantly affected perchlorate adsorption and the zeta potential of AC, while it did not influence perchlorate adsorption and the zeta potential of resin. Zeta potential measurements showed that perchlorate was adsorbed on the negatively charged AC surface. Raman spectra indicated the adsorption resulted in an obvious position shift of the perchlorate peak, suggesting that perchlorate was associated with functional groups on AC at neutral pH through interactions stronger than electrostatic interaction. The adsorbed perchlorate on the resin exhibited a Raman peak at similar position as the aqueous perchlorate, indicating that perchlorate was adsorbed on the resin through electrostatic attraction between the anion and positively charged surface sites.

First-principles calculation of adsorption of shale gas on CaCO3 (100) surfaces.

PubMed

Luo, Qiang; Pan, Yikun; Guo, Ping; Wang, Zhouhua; Wei, Na; Sun, Pengfei; Liu, Yuxiao

2017-06-16

To demonstrate the adsorption strength of shale gas to calcium carbonate in shale matrix, the adsorption of shale gas on CaCO3 (100) surfaces was studied using the first-principles method, which is based on the density functional theory (DFT). The structures and electronic properties of CH4, C2H6, CO2 and N2 molecules were calculated by the generalized gradient approximation (GGA), for a coverage of 1 monolayer (ML). Under the same conditions, the density of states (DOS) of CaCO3 (100) surfaces before and after the adsorption of shale gas molecules at high-symmetry adsorption sites were compared. The results showed that the adsorption energies of CH4, C2H6, CO2 and N2 on CaCO3 (100) surfaces were between 0.2683 eV and -0.7388 eV. When a CH4 molecule was adsorbed at a hollow site and its 2 hydrogen atoms were parallel to the long diagonal (H3) on the CaCO3 (100) surface, it had the most stable adsorption, and the adsorption energy was only -0.4160 eV. The change of adsorption energy of CH4 was no more than 0.0535 eV. Compared with the DOS distribution of CH4 before adsorption, it shifted to the left overall after adsorption. At the same time, the partial density of states (PDOS) curves of CaCO3 (100) surfaces before and after adsorption basically overlapped. This work showed that the adsorption effect of shale gas on calcium carbonate is very weak, and the adsorption is physisorption at the molecular level.

Comparison of hydrogen and deuterium adsorption on Pd(100).

PubMed

Gladys, M J; Kambali, I; Karolewski, M A; Soon, A; Stampfl, C; O'Connor, D J

2010-01-14

Low energy ion recoil spectroscopy is a powerful technique for the determination of adsorbate position on metal surfaces. In this study, this technique is employed to compare the adsorption sites of hydrogen and deuterium on Pd(100) by detection of either H or D recoil ions produced by Ne(+) bombardment. Comparisons of experimental and Kalypso simulated azimuthal yield distributions show that, at room temperature, both hydrogen isotopes are adsorbed in the fourfold hollow site of Pd(100), however, at different heights above the surface (H-0.20 A and D-0.25 A). The adsorbates remain in the hollow site at all temperatures up to 383 K even though they move up to 0.40-0.45 A above the surface. Density functional theory calculations show a similar coverage dependent adsorption height for both H and D and confirm a real difference between the H and D adsorption heights based on zero point energies.

Macromolecule simulation and CH4 adsorption mechanism of coal vitrinite

NASA Astrophysics Data System (ADS)

Yu, Song; Yan-ming, Zhu; Wu, Li

2017-02-01

The microscopic mechanism of interactions between CH4 and coal macromolecules is of significant practical and theoretical importance in CBM development and methane storage. Under periodic boundary conditions, the optimal energy configuration of coal vitrinite, which has a higher torsion degree and tighter arrangement, can be determined by the calculation of molecular mechanics (MM) and molecular dynamics (MD), and annealing kinetics simulation based on ultimate analysis, 13C NMR, FT IR and HRTEM. Macromolecular stabilization is primarily due to the van der Waals energy and covalent bond energy, mainly consisting of bond torsion energy and bond angle energy. Using the optimal configuration as the adsorbent, GCMC simulation of vitrinite adsorption of CH4 is conducted. A saturated state is reached after absorbing 17 CH4s per coal vitrinite molecule. CH4 is preferentially adsorbed on the edge, and inclined to gathering around the branched chains of the inner vitrinite sites. Finally, the adsorption parameters are calculated through first principle DFT. The adsorbability order is as follows: aromatic structure> heteroatom rings > oxygen functional groups. The adsorption energy order is as follows: Top < Bond < Center, Up < Down. The order of average RDF better reflects the adsorption ability and that of [-COOH] is lower than those of [sbnd Cdbnd O] and [Csbnd Osbnd C]. CH4 distributed in the distance of 0.99-16 Å to functional groups in the type of monolayer adsorption and the average distance order manifest as [sbnd Cdbnd O] (1.64 Å) < [Csbnd Osbnd C] (1.89 Å) < [sbnd COOH] (3.78 Å) < [-CH3] (4.11 Å) according to the average RDF curves. CH4 enriches around [sbnd Cdbnd O] and [Csbnd O-C] whereas is rather dispersed about [-COOH] and [CH3]. Simulation and experiment data are both in strong agreement with the Langmuir and D-A isothermal adsorption model and the D-A model fit better than Langmuir model. Preferential adsorption sites and orientations in vitrinite are

Enhancement of elemental mercury adsorption by silver supported material.

PubMed

Khunphonoi, Rattabal; Khamdahsag, Pummarin; Chiarakorn, Siriluk; Grisdanurak, Nurak; Paerungruang, Adjana; Predapitakkun, Somrudee

2015-06-01

Mercury, generally found in natural gas, is extremely hazardous. Although average mercury levels are relatively low, they are further reduced to comply with future mercury regulations, which are stringent in order to avoid releasing to the environment. Herein, vapor mercury adsorption was therefore investigated using two kinds of supports, granular activated carbon (GAC) and titanium dioxide (TiO2). Both supports were impregnated by silver (5 and 15 wt.%), before testing against a commercial adsorbent (sulfur-impregnated activated carbon, SAC). The adsorption isotherm, kinetics, and its thermodynamics of mercury adsorption were reported. The results revealed that Langmuir isotherm provided a better fit to the experimental data. Pseudo second-order was applicable to describe adsorption kinetics. The higher uniform Ag dispersion was a key factor for the higher mercury uptake. TiO2 supported silver adsorbent showed higher mercury adsorption than the commercial one by approximately 2 times. Chemisorption of mercury onto silver active sites was confirmed by an amalgam formation found in the spent adsorbents. Copyright © 2015. Published by Elsevier B.V.

Surface and adsorptive properties of Moringa oleifera bark for removal of V(V) from aqueous solutions.

PubMed

Mnisi, Robert Londi; Ndibewu, Peter Papoh

2017-11-04

The bark of Moringa oleifera, a cheap and readily available natural biopolymeric resource material, found to significantly reduce coliform load and turbidity in contaminated water is investigated in this paper. Its surface and adsorptive properties are investigated to explore its adsorptive potential in removing V(V) from aqueous solutions. Surface properties were investigated using FTIR, HRSEM/EDS, IC, and BET-N 2 adsorption techniques. Adsorptive properties were investigated by optimizing adsorption parameters such as pH, temperature, initial metal concentration, and adsorbent dosage, using V(V) as an adsorbate. The adsorption-desorption isotherms are typical of type II with a H3 hysteresis loop and is characteristic of a largely macroporous material. Bottle ink pores are observed, which can provide good accessibility of the active sites, even though the internal BET surface area is typically low (1.79 g/m 2 ). Solution pH significantly influences the adsorptive potential of the material. The low surface area negatively impacts on the adsorption capacity, but is compensated for by the exchangeable anions (Cl - , F - , PO 4 3- , NO 3 - , and SO 4 2- ) and cations (Ca 2+ , K + , Mg 2+ , and Al 3+ ) at the surface and the accessibility of the active sites. Adsorption isotherm modeling show that the surface is largely heterogeneous with complex multiple sites and adsorption is not limited to monolayer.

p-Chlorophenol adsorption on activated carbons with basic surface properties

NASA Astrophysics Data System (ADS)

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

2010-05-01

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

Structure and adsorption properties of a porous cooper hexacyanoferrate polymorph

NASA Astrophysics Data System (ADS)

Roque-Malherbe, R.; Carballo, E.; Polanco, R.; Lugo, F.; Lozano, C.

2015-11-01

The key questions addressed here were: the structure elucidation and the investigation of the adsorption space and framework expansion effect of a Cu(II) hexacyanoferrate (III) polymorph (labeled Cu-PBA-I). The structural analysis was performed with a broad set of characterization methods. Additionally, a low and high pressure carbon dioxide adsorption investigation was performed, assuming, to comprehend the adsorption experiments, that the adsorbent plus the adsorbed phase were a solid solution. We concluded: that the Cu-PBA-I presented the following composition, K1/4 Cu (II)[ Fe (III)(CN)6 ] 3 / 4⋄1/4 nH2 O , exhibited an antiferromagnetic behavior and displayed a thermally stable I 4 bar m 2 space group lattice in the degassed state. Moreover, the low pressure adsorption study allowed the calculation of the micropore volume, W=0.09 cm3/g and the isosteric heat of adsorption, qiso=19 kJ/mol; further, the high pressure adsorption data revealed an extremely high adsorption capacity owing to a framework expansion effect. Finally, the DRIFTS spectrum of adsorbed CO2 displayed peaks corresponding to carbon dioxide physically adsorbed and interacting with electron accepting Lewis acid sites. Hence, was produced an excellent adsorbent which combine porosity and anti-ferromagnetism, antagonist properties rarely found together.

Adsorption of phenolic compound by aged-refuse.

PubMed

Xiaoli, Chai; Youcai, Zhao

2006-09-01

The adsorption of phenol, 2-chlorophenol, 4-chlorophenol and 2,4-dichlorophenol by aged-refuse has been studied. Adsorption isotherms have been determined for phenol, 2-chlorophenol, 4-chlorophenol and 2,4-dichlorophenol and the data fits well to the Freundlich equation. The chlorinated phenols are absorbed more strongly than the phenol and the adsorption capacity has an oblivious relationship with the numbers and the position of chlorine subsistent. The experiment data suggests that both the partition function and the chemical adsorption involve in the adsorption process. Pseudo-first-order and pseudo-second-order model were applied to investigate the kinetics of the adsorption and the results show that it fit the pseudo-second-order model. More than one step involves in the adsorption process and the overall rate of the adsorption process appears to be controlled by the chemical reaction. The thermodynamic analysis indicates that the adsorption is spontaneous and endothermic.

Gas-phase formaldehyde adsorption isotherm studies on activated carbon: correlations of adsorption capacity to surface functional group density.

PubMed

Carter, Ellison M; Katz, Lynn E; Speitel, Gerald E; Ramirez, David

2011-08-01

Formaldehyde (HCHO) adsorption isotherms were developed for the first time on three activated carbons representing one activated carbon fiber (ACF) cloth, one all-purpose granular activated carbon (GAC), and one GAC commercially promoted for gas-phase HCHO removal. The three activated carbons were evaluated for HCHO removal in the low-ppm(v) range and for water vapor adsorption from relative pressures of 0.1-0.9 at 26 °C where, according to the IUPAC isotherm classification system, the adsorption isotherms observed exhibited Type V behavior. A Type V adsorption isotherm model recently proposed by Qi and LeVan (Q-L) was selected to model the observed adsorption behavior because it reduces to a finite, nonzero limit at low partial pressures and it describes the entire range of adsorption considered in this study. The Q-L model was applied to a polar organic adsorbate to fit HCHO adsorption isotherms for the three activated carbons. The physical and chemical characteristics of the activated carbon surfaces were characterized using nitrogen adsorption isotherms, X-ray photoelectron spectroscopy (XPS), and Boehm titrations. At low concentrations, HCHO adsorption capacity was most strongly related to the density of basic surface functional groups (SFGs), while water vapor adsorption was most strongly influenced by the density of acidic SFGs.

Adsorption of antibiotics on microplastics.

PubMed

Li, Jia; Zhang, Kaina; Zhang, Hua

2018-06-01

Microplastics and antibiotics are two classes of emerging contaminants with proposed negative impacts to aqueous ecosystems. Adsorption of antibiotics on microplastics may result in their long-range transport and may cause compound combination effects. In this study, we investigated the adsorption of 5 antibiotics [sulfadiazine (SDZ), amoxicillin (AMX), tetracycline (TC), ciprofloxacin (CIP), and trimethoprim (TMP)] on 5 types of microplastics [polyethylene (PE), polystyrene (PS), polypropylene (PP), polyamide (PA), and polyvinyl chloride (PVC)] in the freshwater and seawater systems. Scanning Electron Microscope (SEM) and X-ray diffractometer (XRD) analysis revealed that microplastics have different surface characterizes and various degrees of crystalline. Adsorption isotherms demonstrated that PA had the strongest adsorption capacity for antibiotics with distribution coefficient (K d ) values ranged from 7.36 ± 0.257 to 756 ± 48.0 L kg -1 in the freshwater system, which can be attributed to its porous structure and hydrogen bonding. Relatively low adsorption capacity was observed on other four microplastics. The adsorption amounts of 5 antibiotics on PS, PE, PP, and PVC decreased in the order of CIP > AMX > TMP > SDZ > TC with K f correlated positively with octanol-water partition coefficients (Log K ow ). Comparing to freshwater system, adsorption capacity in seawater decreased significantly and no adsorption was observed for CIP and AMX. Our results indicated that commonly observed polyamide particles can serve as a carrier of antibiotics in the aquatic environment. Copyright © 2018 Elsevier Ltd. All rights reserved.

Adsorption mechanism in RPLC. Effect of the nature of the organic modifier

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gritti, Fabrice; Guiochon, Georges A

2005-07-01

The adsorption isotherms of phenol and caffeine were acquired by frontal analysis on two different adsorbents, Kromasil-C{sub 18} and Discovery-C{sub 18}, with two different mobile phases, aqueous solutions of methanol (MeOH/H{sub 2}O = 40/60 and 30/70, v/v) and aqueous solutions of acetonitrile (MeCN/H{sub 2}O = 30/70 and 20/80, v/v). The adsorption isotherms are always strictly convex upward in methanol/water solutions. The calculations of the adsorption energy distribution confirm that the adsorption data for phenol are best modeled with the bi-Langmuir and the tri-Langmuir isotherm models for Kromasil-C{sub 18} and Discovery-C{sub 18}, respectively. Because its molecule is larger and excluded frommore » the deepest sites buried in the bonded layer, the adsorption data of caffeine follow bi-Langmuir isotherm model behavior on both adsorbents. In contrast, with acetonitrile/water solutions, the adsorption data of both phenol and caffeine deviate far less from linear behavior. They were best modeled by the sum of a Langmuir and a BET isotherm models. The Langmuir term represents the adsorption of the analyte on the high-energy sites located within the C{sub 18} layers and the BET term its adsorption on the low-energy sites and its accumulation in an adsorbed multilayer system of acetonitrile on the bonded alkyl chains. The formation of a complex adsorbed phase containing up to four layers of acetonitrile (with a thickness of 3.4 {angstrom} each) was confirmed by the excess adsorption isotherm data measured for acetonitrile on Discovery-C{sub 18}. A simple interpretation of this change in the isotherm curvature at high concentrations when methanol is replaced with acetonitrile as the organic modifier is proposed, based on the structure of the interface between the C{sub 18} chains and the bulk mobile phase. This new model accounts for all the experimental observations.« less

Protein Adsorption in Three Dimensions

PubMed Central

Vogler, Erwin A.

2011-01-01

Recent experimental and theoretical work clarifying the physical chemistry of blood-protein adsorption from aqueous-buffer solution to various kinds of surfaces is reviewed and interpreted within the context of biomaterial applications, especially toward development of cardiovascular biomaterials. The importance of this subject in biomaterials surface science is emphasized by reducing the “protein-adsorption problem” to three core questions that require quantitative answer. An overview of the protein-adsorption literature identifies some of the sources of inconsistency among many investigators participating in more than five decades of focused research. A tutorial on the fundamental biophysical chemistry of protein adsorption sets the stage for a detailed discussion of the kinetics and thermodynamics of protein adsorption, including adsorption competition between two proteins for the same adsorbent immersed in a binary-protein mixture. Both kinetics and steady-state adsorption can be rationalized using a single interpretive paradigm asserting that protein molecules partition from solution into a three-dimensional (3D) interphase separating bulk solution from the physical-adsorbent surface. Adsorbed protein collects in one-or-more adsorbed layers, depending on protein size, solution concentration, and adsorbent surface energy (water wettability). The adsorption process begins with the hydration of an adsorbent surface brought into contact with an aqueous-protein solution. Surface hydration reactions instantaneously form a thin, pseudo-2D interface between the adsorbent and protein solution. Protein molecules rapidly diffuse into this newly-formed interface, creating a truly 3D interphase that inflates with arriving proteins and fills to capacity within milliseconds at mg/mL bulk-solution concentrations CB. This inflated interphase subsequently undergoes time-dependent (minutes-to-hours) decrease in volume VI by expulsion of either-or-both interphase water and

Highly Selective Adsorption of Ethylene over Ethane in a MOF Featuring the Combination of Open Metal Site and -Complexation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Yiming; Li, Baiyan; Wu, Zili

The introduction of the combination of open metal site (OMS) and -complexation into MOF has led to very high ethylene/ethane adsorption selectivity at 318K, as illustrated in the context of MIL-101-Cr-SO 3Ag. The interactions with ethylene from both OMS and -complexation in MIL-101-Cr-SO 3Ag have been investigated by in situ IR spectroscopic studies and computational calculations, which suggest -complexation contributes dominantly to the high ethylene/ethane adsorption selectivity.

Highly Selective Adsorption of Ethylene over Ethane in a MOF Featuring the Combination of Open Metal Site and -Complexation

DOE PAGES

Zhang, Yiming; Li, Baiyan; Wu, Zili; ...

2015-01-09

The introduction of the combination of open metal site (OMS) and -complexation into MOF has led to very high ethylene/ethane adsorption selectivity at 318K, as illustrated in the context of MIL-101-Cr-SO 3Ag. The interactions with ethylene from both OMS and -complexation in MIL-101-Cr-SO 3Ag have been investigated by in situ IR spectroscopic studies and computational calculations, which suggest -complexation contributes dominantly to the high ethylene/ethane adsorption selectivity.

Adsorption of thiophene on silica-supported Mo clusters

NASA Astrophysics Data System (ADS)

Komarneni, M.; Kadossov, E.; Justin, J.; Lu, M.; Burghaus, U.

2010-07-01

The adsorption/decomposition kinetics/dynamics of thiophene has been studied on silica-supported Mo and MoS x clusters. Two-dimensional cluster formation at small Mo exposures and three-dimensional cluster growth at larger exposures would be consistent with the Auger electron spectroscopy (AES) data. Thermal desorption spectroscopy (TDS) indicates two reaction pathways. H 4C 4S desorbs molecularly at 190-400 K. Two TDS features were evident and could be assigned to molecularly on Mo sites, and S sites adsorbed thiophene. Assuming a standard preexponential factor (ν = 1 × 10 13/s) for first-order kinetics, the binding energies for adsorption on Mo (sulfur) sites amount to 90 (65) kJ/mol for 0.4 ML Mo exposure and 76 (63) kJ/mol for 2 ML Mo. Thus, smaller clusters are more reactive than larger clusters for molecular adsorption of H 4C 4S. The second reaction pathway, the decomposition of thiophene, starts at 250 K. Utilizing multimass TDS, H 2, H 2S, and mostly alkynes are detected in the gas phase as decomposition products. H 4C 4S bond activation results in partially sulfided Mo clusters as well as S and C residuals on the surface. S and C poison the catalyst. As a result, with an increasing number of H 4C 4S adsorption/desorption cycles, the uptake of molecular thiophene decreases as well as the H 2 and H 2S production ceases. Thus, silica-supported sulfided Mo clusters are less reactive than metallic clusters. The poisoned catalyst can be partially reactivated by annealing in O 2. However, Mo oxides also appear to form, which passivate the catalyst further. On the other hand, while annealing a used catalyst in H/H 2, it is poisoned even more (i.e., the S AES signal increases). By means of adsorption transients, the initial adsorption probability, S0, of C 4H 4S has been determined. At thermal impact energies ( Ei = 0.04 eV), S0 for molecular adsorption amounts to 0.43 ± 0.03 for a surface temperature of 200 K. S0 increases with Mo cluster size, obeying the

Quantum chemical study of arsenic (III, V) adsorption on Mn-oxides: implications for arsenic(III) oxidation.

PubMed

Zhu, Mengqiang; Paul, Kristian W; Kubicki, James D; Sparks, Donald L

2009-09-01

Density functional theory (DFT) calculations were used to investigate As(V) and As(III) surface complex structures and reaction energies on both Mn(III) and Mn(IV) sites in an attempt to better understand As(III) oxidation bybirnessite, a layered Mn-dioxide mineral. Edge-sharing dioctahedral Mn(III) and Mn(IV) clusters with different combinations of surface functional groups (>MnOH and >MnOH2) were employed to mimic pH variability. Results show that As(V) adsorption was more thermodynamically favorable than As(III) adsorption on both Mn(III) and Mn(IV) surface sites under simulated acidic pH conditions. Therefore, we propose that As(V) adsorption inhibits As(III) oxidation by blocking adsorption sites. Under simulated acidic pH conditions, Mn(IV) sites exhibited stronger adsorption affinity than Mn(III) sites for both As(III) and As(V). Overall, we hypothesize that Mn(III) sites are less reactive in terms of As(III) oxidation due to their lower affinity for As(III) adsorption, higher potential to be blocked by As(V) complexes, and slower electron transfer rates with adsorbed As(III). Results from this study offer an explanation regarding the experimental observations of Mn(III) accumulation on birnessite and the long residence time of As(III) adsorption complexes on manganite (r-MnOOH) during As(III) oxidation.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Da-Jiang; Evans, James W.

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

Oxygen adsorption on the Al0.25Ga0.75N (0001) surface: A first-principles study

NASA Astrophysics Data System (ADS)

Fu, Jiaqi; Song, Tielei; Liang, Xixia; Zhao, Guojun

2018-04-01

To understand the interaction mechanism for the oxygen adsorption on AlGaN surface, herein, we built the possible models of oxygen adsorption on Al0.25Ga0.75N (0001) surface. For different oxygen coverage, three kinds of adsorption site are considered. Then the favorable adsorption sites are characterized by first principles calculation for (2 × 2) supercell of Al0.25Ga0.75N (0001) surface. On basis of the optimal adsorption structures, our calculated results show that all the adsorption processes are exothermic, indicating that the (0001) surface orientation is active towards the adsorption of oxygen. The doping of Al is advantage to the adsorption of O atom. Additionally, the adsorption energy decreases with reducing the oxygen coverage, and the relationship between them is approximately linear. Owing to the oxygen adsorption, the surface states in the fundamental band gap are significant reduced with respect to the free Al0.25Ga0.75N (0001) surface. Moreover, the optical properties on different oxygen coverage are also discussed.

Liquid-Phase Adsorption Fundamentals.

ERIC Educational Resources Information Center

Cooney, David O.

1987-01-01

Describes an experiment developed and used in the unit operations laboratory course at the University of Wyoming. Involves the liquid-phase adsorption of an organic compound from aqueous solution on activated carbon, and is relevant to adsorption processes in general. (TW)

Adsorption of thiophene on transition metal surfaces with the inclusion of van der Waals effects

NASA Astrophysics Data System (ADS)

Malone, Walter; Matos, Jeronimo; Kara, Abdelkader

2018-03-01

We use density functional theory with the inclusion of the van der Waals interaction to study the adsorption of thiophene, C4H4S, on Pt, Rh, Pd, Au, and Ag (100) surfaces. The five van der Waals (vdW) inclusive functionals we employ are optB86b-vdW, optB88-vdW, optPBE-vdW, revPBE-vdW, and rPW86-vdW2. For comparison we also run calculations with the GGA- Perdew Burke and Ernzerhof (PBE) functional. We examine several adsorption sites with the plane of the molecule parallel or perpendicular to the surface. The most stable configuration on all metals was the site where the center of the thiophene lies over a 4-fold hollow site with the sulfur atom lying close to a top site. Furthermore, we examine several electronic and geometric properties of the adsorbate including charge transfer, modification of the d-band, adsorption energy, tilt angle, and adsorption height. For the coinage metals PBE gives the lowest adsorption energy. For reactive transition metal substrates, revPBE-vdW and rPW86-vdW2 give lower adsorption energies than PBE.

Metal adsorption onto bacterial surfaces: development of a predictive approach

NASA Astrophysics Data System (ADS)

Fein, Jeremy B.; Martin, Aaron M.; Wightman, Peter G.

2001-12-01

Aqueous metal cation adsorption onto bacterial surfaces can be successfully modeled by means of a surface complexation approach. However, relatively few stability constants for metal-bacterial surface complexes have been measured. In order to determine the bacterial adsorption behavior of cations that have not been studied in the laboratory, predictive techniques are required that enable estimation of the stability constants of bacterial surface complexes. In this study, we use a linear free-energy approach to compare previously measured stability constants for Bacillus subtilis metal-carboxyl surface complexes with aqueous metal-organic acid anion stability constants. The organic acids that we consider are acetic, oxalic, citric, and tiron. We add to this limited data set by conducting metal adsorption experiments onto Bacillus subtilis, determining bacterial surface stability constants for Co, Nd, Ni, Sr, and Zn. The adsorption behavior of each of the metals studied here was described well by considering metal-carboxyl bacterial surface complexation only, except for the Zn adsorption behavior, which required carboxyl and phosphoryl complexation to obtain a suitable fit to the data. The best correlation between bacterial carboxyl surface complexes and aqueous organic acid anion stability constants was obtained by means of metal-acetate aqueous complexes, with a linear correlation coefficient of 0.97. This correlation applies only to unhydrolyzed aqueous cations and only to carboxyl binding of those cations, and it does not predict the binding behavior under conditions where metal binding to other bacterial surface site types occurs. However, the relationship derived in this study permits estimation of the carboxyl site adsorption behavior of a wide range of aqueous metal cations for which there is an absence of experimental data. This technique, coupled with the observation of similar adsorption behaviors across bacterial species (Yee and Fein, 2001), enables

Phosphate adsorption performance of a novel filter substrate made from drinking water treatment residuals.

PubMed

Wang, Wendong; Ma, Cui; Zhang, Yinting; Yang, Shengjiong; Shao, Yue; Wang, Xiaochang

2016-07-01

Phosphate is one of the most predominant pollutants in natural waters. Laboratory experiments were conducted to investigate the phosphate adsorption performance of a (NFS) made from drinking water treatment residuals. The adsorption of phosphate on the NFS fitted well with the Freundlich isotherm and pseudo second-order kinetic models. At pH7.0, the maximum adsorption capacity of 1.03mg/g was achieved at 15°C corresponding to the wastewater temperature in cold months, and increased notably to 1.31mg/g at 35°C. Under both acidic conditions (part of the adsorption sites was consumed) and basic conditions (negative charges formed on the surface of NFS, which led to a static repulsion of PO4(3-) and HPO4(2-)), the adsorption of phosphate was slightly inhibited. Further study showed that part of the adsorption sites could be recovered by 0.25mol/L NaOH. The activation energy was calculated to be above 8.0kJ/mol, indicating that the adsorption of phosphate on NFS was probably a chemical process. Considering the strong phosphate adsorption capacity and recoverability, NFS showed great promise on enhancing phosphate removal from the secondary treated wastewater in the filtration process. Copyright © 2016. Published by Elsevier B.V.

Adsorption of ion pairs onto graphene flakes and impacts of counterions during the adsorption processes

NASA Astrophysics Data System (ADS)

Zhu, Chang; Yun, Jiena; Wang, Qian; Yang, Gang

2018-03-01

Although cations and anions are two integral constituents for all electrolytes, adsorption of ion pairs onto carbonaceous materials gains obviously less attention than adsorption of only cations or anions. Here DFT calculations are employed finding that four adsorption configurations emerge for KI onto graphene flakes (GF) instead of three for the other ion pairs. Reservation of ionic bonds is critical to their stabilities, and the bilateral configurations, where GFs couple with both cations and anions, are disfavored due to rupture of ionic bonds. Relative stabilities of two vertical configurations can be regulated and even reversed through edge-functionalization. Surprisingly, the horizontal adsorption configurations, which are global energy minima as long as present, are non-existent for a majority of ion pairs, and their existence or not is determined by the adsorption differences between halide ions and alkali ions (△Ead). Counterions effects for both cations and anions increase with the atomic electronegativities and cations correspond to stronger counterion effects; e.g., Li+ added on the other side of GFs promotes the adsorption of F- more pronouncedly than edge-functionalization. Mechanisms of electron transfers are also discussed, and three alteration patterns by counterions are observed for each type of adsorption configurations. Furthermore, addition of counterions causes band gaps to vary within a wider range that may be useful to design electronic devices.

Adsorption dynamics of methyl violet onto granulated mesoporous carbon: Facile synthesis and adsorption kinetics.

PubMed

Kim, Yohan; Bae, Jiyeol; Park, Hosik; Suh, Jeong-Kwon; You, Young-Woo; Choi, Heechul

2016-09-15

A new and facile one-step synthesis method for preparing granulated mesoporous carbon (GMC) with three-dimensional spherical mesoporous symmetry is prepared to remove large molecular weight organic compounds in aqueous phase. GMC is synthesized in a single step using as-synthesized mesoporous carbon particles and organic binders through a simple and economical synthesis approach involving a simultaneous calcination and carbonization process. Characterization results obtained from SEM, XRD, as well as surface and porosity analysis indicate that the synthesized GMC has similar physical properties to those of the powdered mesoporous carbon and maintains the Brunauer-Emmett-Teller (BET) surface area and pore volume because the new synthesis method prevents the collapse of the pores during the granulation process. Batch adsorption experiments revealed GMC showed a substantial adsorption capacity (202.8 mg/g) for the removal of methyl violet as a target large molecular contaminant in aqueous phase. The mechanisms and dynamics modeling of GMC adsorption were also fully examined, which revealed that surface diffusion was rate limiting step on adsorption process of GMC. Adsorption kinetics of GMC enables 3 times faster than that of granular activated carbon in terms of surface diffusion coefficient. This is the first study, to the best of our knowledge, to synthesize GMC as an adsorbent for water purification by using facile granulation method and to investigate the adsorption kinetics and characteristics of GMC. This study introduces a new and simple method for the synthesis of GMC and reveals its adsorption characteristics for large molecular compounds in a water treatment. Copyright © 2016 Elsevier Ltd. All rights reserved.

Theoretical Studies about Adsorption on Silicon Surface

NASA Astrophysics Data System (ADS)

Huang, Yan; Chen, Xiaoshuang; Zhu, Xiao Yan; Duan, He; Zhou, Xiao Hao; Lu, Wei

In this review paper, we address the important research topic of adsorption on the silicon surface. The deposition of single Si ad-species (adatom and ad-dimer) on the p(2×2) reconstructed Si(100) surface has been simulated by the empirical tight-binding method. Using the clean and defective Si surfaces as the deposition substrates, the deposition energies are mapped out around the clean surface, dimer vacancies, steps and kink structures. The binding sites, saddle points and several possible diffusion paths are obtained from the calculated energy. With further analysis of the deposition and diffusion behaviors, the influences of the surface defects can be found. Then, by adopting the first-principle calculations, the adsorptions of the II-VI group elements on the clean and As-passivated Si(211) substrates have been calculated as the example of adsorption on the high-miller-index Si surface.

A DFT+U investigation of hydrogen adsorption on the LaFeO3(010) surface.

PubMed

Boateng, Isaac W; Tia, Richard; Adei, Evans; Dzade, Nelson Y; Catlow, C Richard A; de Leeuw, Nora H

2017-03-08

The ABO 3 perovskite lanthanum ferrite (LaFeO 3 ) is a technologically important electrode material for nickel-metal hydride batteries, energy storage and catalysis. However, the electrochemical hydrogen adsorption mechanism on LaFeO 3 surfaces remains under debate. In the present study, we have employed spin-polarized density functional theory calculations, with the Hubbard U correction (DFT+U), to unravel the adsorption mechanism of H 2 on the LaFeO 3 (010) surface. We show from our calculated adsorption energies that the preferred site for H 2 adsorption is the Fe-O bridge site, with an adsorption energy of -1.18 eV (including the zero point energy), which resulted in the formation of FeOH and FeH surface species. H 2 adsorption at the surface oxygen resulted in the formation of a water molecule, which leaves the surface to create an oxygen vacancy. The H 2 molecule is found to interact weakly with the Fe and La sites, where it is only physisorbed. The electronic structures of the surface-adsorption systems are discussed via projected density of state and Löwdin population analyses. The implications of the calculated adsorption strengths and structures are discussed in terms of the improved design of nickel-metal hydride (Ni-MH) battery prototypes based on LaFeO 3 .

Theoretical study of adsorption of organic phosphines on transition metal surfaces

NASA Astrophysics Data System (ADS)

Lou, Shujie; Jiang, Hong

2018-04-01

The adsorption properties of organic phosphines on transition metal (TM) surfaces (Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Ir, Pt, and Au) have been studied to explore the possibility of building novel heterogeneous chiral catalytic systems based on organic phosphines. Preferred adsorption sites, adsorption energies and surface electronic structures of a selected set of typical organic phosphines adsorbed on TM surfaces are calculated with density-functional theory to obtain a systematic understanding on the nature of adsorption interactions. All organic phosphines considered are found to chemically adsorb on these TM surfaces with the atop site as the most preferred one, and the TM-P bond is formed via the lone-pair electrons of the P atom and the directly contacted TM atom. These findings imply that it is indeed possible to build heterogeneous chiral catalytic systems based on organic phosphines adsorbed on TM surfaces, which, however, requires a careful design of molecular structure of organic phosphines.

Adsorption--from theory to practice.

PubMed

Dabrowski, A

2001-10-08

Adsorption at various interfaces has concerned scientists since the beginning of this century. This phenomenon underlies a number of extremely important processes of utilitarian significance. The technological, environmental and biological importance of adsorption can never be in doubt. Its practical applications in industry and environmental protection are of paramount importance. The adsorption of substrates is the first stage in many catalytic processes. The methods for separation of mixtures on a laboratory and on an industrial scale are increasingly based on utilising the change in concentration of components at the interface. Moreover, such vital problems as purification of water, sewages, air and soil are involved here too. On the other hand, many areas in which technological innovation has covered adsorption phenomena have been expanded more through art and craft than through science. A basic understanding of the scientific principles is far behind; in part because the study of interfaces requires extremely careful experimentation if meaningful and reproducible results are to be obtained. In recent years, however, considerable effort has been increasingly directed toward closing the gap between theory and practice. Crucial progress in theoretical description of the adsorption has been achieved, mainly through the development of new theoretical approaches formulated on a molecular level, by means of computer simulation methods and owing to new techniques which examine surface layers or interfacial regions. Moreover, during the last 15 years new classes of solid adsorbents have been developed, such as activated carbon fibres and carbon molecular sieves, fullerenes and heterofullerenes, microporous glasses and nanoporous--both carbonaceous and inorganic--materials. Nanostructured solids are very popular in science and technology and have gained extreme interest due to their sorption, catalytic, magnetic, optical and thermal properties. Although the development

The adsorption of HCl on volcanic ash

NASA Astrophysics Data System (ADS)

Gutiérrez, Xochilt; Schiavi, Federica; Keppler, Hans

2016-03-01

Understanding the interaction between volcanic gases and ash is important to derive gas compositions from ash leachates and to constrain the environmental impact of eruptions. Volcanic HCl could potentially damage the ozone layer, but it is unclear what fraction of HCl actually reaches the stratosphere. The adsorption of HCl on volcanic ash was therefore studied from -76 to +150 °C to simulate the behavior of HCl in the dilute parts of a volcanic plume. Finely ground synthetic glasses of andesitic, dacitic, and rhyolitic composition as well as a natural obsidian from Vulcano (Italy) served as proxies for fresh natural ash. HCl adsorption is an irreversible process and appears to increase with the total alkali content of the glass. Adsorption kinetics follow a first order law with rate constants of 2.13 ṡ10-6 s-1 to 1.80 ṡ10-4 s-1 in the temperature range investigated. For dacitic composition, the temperature and pressure dependence of adsorption can be described by the equation ln ⁡ c = 1.26 + 0.27 ln ⁡ p - 715.3 / T, where c is the surface concentration of adsorbed HCl in mg/m2, T is temperature in Kelvin, and p is the partial pressure of HCl in mbar. A comparison of this model with a large data set for the composition of volcanic ash suggests that adsorption of HCl from the gas phase at relatively low temperatures can quantitatively account for the majority of the observed Cl concentrations. The model implies that adsorption of HCl on ash increases with temperature, probably because of the increasing number of accessible adsorption sites. This temperature dependence is opposite to that observed for SO2, so that HCl and SO2 are fractionated by the adsorption process and the fractionation factor changes by four orders of magnitude over a temperature range of 250 K. The assumption of equal adsorption of different species is therefore not appropriate for deriving volcanic gas compositions from analyses of adsorbates on ash. However, with the experimental

The Adsorption of Cd(II) on Manganese Oxide Investigated by Batch and Modeling Techniques.

PubMed

Huang, Xiaoming; Chen, Tianhu; Zou, Xuehua; Zhu, Mulan; Chen, Dong; Pan, Min

2017-09-28

Manganese (Mn) oxide is a ubiquitous metal oxide in sub-environments. The adsorption of Cd(II) on Mn oxide as function of adsorption time, pH, ionic strength, temperature, and initial Cd(II) concentration was investigated by batch techniques. The adsorption kinetics showed that the adsorption of Cd(II) on Mn oxide can be satisfactorily simulated by pseudo-second-order kinetic model with high correlation coefficients (R² > 0.999). The adsorption of Cd(II) on Mn oxide significantly decreased with increasing ionic strength at pH < 5.0, whereas Cd(II) adsorption was independent of ionic strength at pH > 6.0, which indicated that outer-sphere and inner-sphere surface complexation dominated the adsorption of Cd(II) on Mn oxide at pH < 5.0 and pH > 6.0, respectively. The maximum adsorption capacity of Mn oxide for Cd(II) calculated from Langmuir model was 104.17 mg/g at pH 6.0 and 298 K. The thermodynamic parameters showed that the adsorption of Cd(II) on Mn oxide was an endothermic and spontaneous process. According to the results of surface complexation modeling, the adsorption of Cd(II) on Mn oxide can be satisfactorily simulated by ion exchange sites (X₂Cd) at low pH and inner-sphere surface complexation sites (SOCd⁺ and (SO)₂CdOH - species) at high pH conditions. The finding presented herein plays an important role in understanding the fate and transport of heavy metals at the water-mineral interface.

The Adsorption of Cd(II) on Manganese Oxide Investigated by Batch and Modeling Techniques

PubMed Central

Huang, Xiaoming; Chen, Tianhu; Zou, Xuehua; Zhu, Mulan; Chen, Dong

2017-01-01

Manganese (Mn) oxide is a ubiquitous metal oxide in sub-environments. The adsorption of Cd(II) on Mn oxide as function of adsorption time, pH, ionic strength, temperature, and initial Cd(II) concentration was investigated by batch techniques. The adsorption kinetics showed that the adsorption of Cd(II) on Mn oxide can be satisfactorily simulated by pseudo-second-order kinetic model with high correlation coefficients (R2 > 0.999). The adsorption of Cd(II) on Mn oxide significantly decreased with increasing ionic strength at pH < 5.0, whereas Cd(II) adsorption was independent of ionic strength at pH > 6.0, which indicated that outer-sphere and inner-sphere surface complexation dominated the adsorption of Cd(II) on Mn oxide at pH < 5.0 and pH > 6.0, respectively. The maximum adsorption capacity of Mn oxide for Cd(II) calculated from Langmuir model was 104.17 mg/g at pH 6.0 and 298 K. The thermodynamic parameters showed that the adsorption of Cd(II) on Mn oxide was an endothermic and spontaneous process. According to the results of surface complexation modeling, the adsorption of Cd(II) on Mn oxide can be satisfactorily simulated by ion exchange sites (X2Cd) at low pH and inner-sphere surface complexation sites (SOCd+ and (SO)2CdOH− species) at high pH conditions. The finding presented herein plays an important role in understanding the fate and transport of heavy metals at the water–mineral interface. PMID:28956849

Adsorption of octylamine on titanium dioxide

NASA Astrophysics Data System (ADS)

Siwińska, Daria; Kołodziejczak-Radzimska, Agnieszka; Krysztafkiewicz, Andrzej; Jesionowski, Teofil

2009-05-01

Processes of adsorption and desorption of a model active substance (octylamine) on the surface of unmodified titanium dioxide (E 171) have been performed. The effects of concentration of octylamine and time of the process on the character of adsorption have been studied and the efficiency of the adsorption/desorption has been determined. The samples obtained have been studied by X-ray diffraction. The nitrogen adsorption/desorption isotherms, particle size distribution and absorption capacities of water, dibutyl phthalate and paraffin oil have been determined. The efficiency of octylamine adsorption on the surface of the titanium dioxide has been found positively correlated with the concentration of octylamine in the initial solution. The desorption of octylamine has decreased with increasing concentration of this compound adsorbed. For octylamine in low concentrations the physical adsorption has been found to dominate, which is desirable when using TiO 2 in the production of pharmaceuticals.

Recovery oriented phosphorus adsorption process in decentralized advanced Johkasou.

PubMed

Ebie, Y; Kondo, T; Kadoya, N; Mouri, M; Maruyama, O; Noritake, S; Inamori, Y; Xu, K

2008-01-01

Decentralized advanced wastewater treatment using adsorption and desorption process for recovery and recycling oriented phosphorus removal was developed. Adsorbent particles made of zirconium were set in a column, and it was installed as subsequent stage of BOD and nitrogen removal type Johkasou, a household domestic wastewater treatment facility. The water quality of the effluent of adsorption column in a number of experimental sites was monitored. The effluent phosphorus concentration was kept below 1 mg l(-1) during 90 days at all the sites. Furthermore, over 80% of the sites achieved 1 mg l(-1) of T-P during 200 days. This adsorbent was durable, and deterioration of the particles was not observed over a long duration. The adsorbent collected from each site was immersed in alkali solution to desorb phosphorus. Then the adsorbent was reactivated by soaking in acid solution. The reactivated adsorbent was reused and showed almost the same phosphorus adsorption capacity as a new one. Meanwhile, the desorbed phosphorus was recovered with high purity as trisodium phosphate by crystallization. It is proposed as a new decentralized system for recycling phosphorus that paves the way to high-purity recovery of finite phosphorus. IWA Publishing 2008.

Adsorption of lactic acid on chiral Pt surfaces—A density functional theory study

NASA Astrophysics Data System (ADS)

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

2013-02-01

The adsorption of the chiral molecule lactic acid on chiral Pt surfaces is studied by density functional theory calculations. First, we study the adsorption of L-lactic acid on the flat Pt(111) surface. Using the optimed PBE - van der Waals (oPBE-vdW) functional, which includes van der Waals forces on an ab initio level, it is shown that the molecule has two binding sites, a carboxyl and the hydroxyl oxygen atoms. Since real chiral surfaces are (i) known to undergo thermal roughening that alters the distribution of kinks and step edges but not the overall chirality and (ii) kink sites and edge sites are usually the energetically most favored adsorption sites, we focus on two surfaces that allow qualitative sampling of the most probable adsorption sites. We hereby consider chiral surfaces exhibiting (111) facets, in particular, Pt(321) and Pt(643). The binding sites are either both on kink sites—which is the case for Pt(321) or on one kink site—as on Pt(643). The binding energy of the molecule on the chiral surfaces is much higher than on the Pt(111) surface. We show that the carboxyl group interacts more strongly than the hydroxyl group with the kink sites. The results indicate the possible existence of very small chiral selectivities of the order of 20 meV for the Pt(321) and Pt(643) surfaces. L-lactic acid is more stable on Pt(321)S than D-lactic acid, while the chiral selectivity is inverted on Pt(643)S. The most stable adsorption configurations of L- and D-lactic acid are similar for Pt(321) but differ for Pt(643). We explore the impact of the different adsorption geometries on the work function, which is important for field ion microscopy.

[Treatment of organic waste gas by adsorption rotor].

PubMed

Zhu, Run-Ye; Zheng, Liang-Wei; Mao, Yu-Bo; Wang, Jia-De

2013-12-01

The adsorption rotor is applicable to treating organic waste gases with low concentration and high air volume. The performance of adsorption rotor for purifying organic waste gases was investigated in this paper. Toluene was selected as the simulative gaseous pollutant and the adsorption rotor was packed with honeycomb modified 13X molecular sieves (M-13X). Experimental results of the fixed adsorption and the rotor adsorption were analyzed and compared. The results indicated that some information on the fixed adsorption was useful for the rotor adsorption. Integrating the characteristics of the adsorbents, waste gases and the structures of the rotor adsorption, the formulas on optimal rotor speed and cycle removal efficiency of the adsorption rotor were deduced, based on the mass and heat balances of the adsorbing process. The numerical results were in good agreement with the experimental data, which meant that the formulas on optimal rotor speed and cycle removal efficiency could be effectively applied in design and operation of the adsorption rotor.

A fundamental study of the impact of pressure on the adsorption mechanism in reversed-phase liquid chromatography.

PubMed

Åsberg, Dennis; Samuelsson, Jörgen; Fornstedt, Torgny

2016-07-29

A fundamental investigation of the pressure effect on individual adsorption sites was undertaken based on adsorption energy distribution and adsorption isotherm measurements. For this purpose, we measured adsorption equilibrium data at pressures ranging from 100 to 1000bar at constant flow and over a wide concentration range for three low-molecular-weight solutes, antipyrine, sodium 2-naphthalenesulfonate, and benzyltriethylammonium chloride, on an Eternity C18 stationary phase. The adsorption energy distribution was bimodal for all solutes, remaining clearly so at all pressures. The bi-Langmuir model best described the adsorption in these systems and two types of adsorption sites were identified, one with a low and another with a high energy of interaction. Evidence exists that the low-energy interactions occur at the interface between the mobile and stationary phases and that the high-energy interactions occur nearer the silica surface, deeper in the C18 layer. The contribution of each type of adsorption site to the retention factor was calculated and the change in solute molar volume from the mobile to stationary phase during the adsorption process was estimated for each type of site. The change in solute molar volume was 2-4 times larger at the high-energy site, likely because of the greater loss of solute solvation layer when penetrating deeper into the C18 layer. The association equilibrium constant increased with increasing pressure while the saturation capacity of the low-energy site remained almost unchanged. The observed increase in saturation capacity for the high-energy site did not affect the column loading capacity, which was almost identical at 50- and 950-bar pressure drops over the column. Copyright © 2016 Elsevier B.V. All rights reserved.

Effect of humic acid preloading on phosphate adsorption onto zirconium-modified zeolite.

PubMed

Lin, Jianwei; Zhang, Zhe; Zhan, Yanhui

2017-05-01

A zirconium-modified zeolite (ZrMZ) was prepared, and then, humic acid (HA) was immobilized on the ZrMZ surface to prepare HA-loaded ZrMZ (HA-ZrMZ). The obtained ZrMZ and HA-ZrMZ were characterized by energy dispersive X-ray spectroscopy, elemental analyzer, N 2 adsorption/desorption isotherms, pH at the point of zero charge, and X-ray photoelectron spectroscopy. The adsorption characteristics of phosphate on ZrMZ and HA-ZrMZ were comparatively investigated in batch mode. The adsorption mechanism of phosphate on ZrMZ and HA-ZrMZ was investigated by ionic strength effect and 31 P nuclear magnetic resonance. The mechanism for phosphate adsorption onto ZrMZ was the formation of inner-sphere phosphate complexes at the solid/solution interface. The preloading of HA on ZrMZ reduced the phosphate adsorption capacity, and the more the HA loading amount, the lower the phosphate adsorption capacity. However, the preloading of HA on ZrMZ did not change the phosphate adsorption mechanism; i.e., the formation of inner-sphere phosphate surface complexes was still responsible for the adsorption of phosphate on HA-ZrMZ. The decreased phosphate adsorption capacity for ZrMZ after HA coating could be attributed to the fact that the coating of HA on ZrMZ reduced the amount of binding active sites available for phosphate adsorption, changed the adsorbent surface charges, and reduced the specific surface areas and pore volumes of ZrMZ.

Adsorption and co-adsorption of diclofenac and Cu(II) on calcareous soils.

PubMed

Graouer-Bacart, Mareen; Sayen, Stéphanie; Guillon, Emmanuel

2016-02-01

Pharmaceuticals are emerging contaminants and their presence in different compartments of the environment has been detected in many countries. In this study, laboratory batch experiments were conducted to characterize the adsorption of diclofenac, a widely used non-steroidal anti-inflammatory drug, on six calcareous soils. The adsorption of diclofenac was relatively low, which may lead to a risk of groundwater contamination and plant uptake. A correlation between the soil-water distribution coefficient Kd and soil characteristics has been highlighted. Indeed, diclofenac adsorption as a function of soil organic matter content (% OM) and Rt=% CaCO3/% OM was successfully described through a simple empirical model, indicating the importance of considering the inhibiting effect of CaCO3 on OM retention properties for a better assessment of diclofenac fate in the specific case of calcareous soils. The simultaneous co-adsorption of diclofenac and copper - a ubiquitous pollutant in the environment - at the water/soil interface, was also investigated. It appeared quite unexpectedly that copper did not have a significant influence on diclofenac retention. Copyright © 2015 Elsevier Inc. All rights reserved.

Chirality in adsorption on solid surfaces.

PubMed

Zaera, Francisco

2017-12-07

In the present review we survey the main advances made in recent years on the understanding of chemical chirality at solid surfaces. Chirality is an important topic, made particularly relevant by the homochiral nature of the biochemistry of life on Earth, and many chiral chemical reactions involve solid surfaces. Here we start our discussion with a description of surface chirality and of the different ways that chirality can be bestowed on solid surfaces. We then expand on the studies carried out to date to understand the adsorption of chiral compounds at a molecular level. We summarize the work published on the adsorption of pure enantiomers, of enantiomeric mixtures, and of prochiral molecules on chiral and achiral model surfaces, especially on well-defined metal single crystals but also on other flat substrates such as highly ordered pyrolytic graphite. Several phenomena are identified, including surface reconstruction and chiral imprinting upon adsorption of chiral agents, and the enhancement or suppression of enantioselectivity seen in some cases upon adsorption of enantiomixtures of chiral compounds. The possibility of enhancing the enantiopurity of adsorbed layers upon the addition of chiral seeds and the so-called "sergeants and soldiers" phenomenon are presented. Examples are provided where the chiral behavior has been associated with either thermodynamic or kinetic driving forces. Two main approaches to the creation of enantioselective surface sites are discussed, namely, via the formation of supramolecular chiral ensembles made out of small chiral adsorbates, and by adsorption of more complex chiral molecules capable of providing suitable chiral environments for reactants by themselves, via the formation of individual adsorbate:modifier adducts on the surface. Finally, a discussion is offered on the additional effects generated by the presence of the liquid phase often required in practical applications such as enantioselective crystallization, chiral

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

USGS Publications Warehouse

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

1994-01-01

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

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…

A periodic DFT study of ammonia adsorption on the V2O5 (001), V2O5 (010) and V2O5 (100) surfaces: Lewis versus Brönsted acid sites

NASA Astrophysics Data System (ADS)

Yao, Huichao; Chen, Yu; Wei, Yuechang; Zhao, Zhen; Liu, Zhichang; Xu, Chunming

2012-11-01

The adsorption of ammonia at Brönsted and Lewis acid sites on three low-index (001), (010) and (100) surfaces of V2O5 catalyst was investigated using density functional theory (DFT) method. Three levels of surface relaxation periodic models including top single layer relaxation (S-model), moderately deeper relaxation (M-model) and full relaxation model (F-model) were applied to examine the effect of the surface relaxation on the binding structures and adsorption energies. The results of calculations showed that on the saturated basal plane V2O5 (001), ammonia adsorption at the Brönsted acid sites (VOH) is energetically more favorable. On unsaturated (010) and (100) surfaces, ammonia is adsorbed strongly on both Brönsted (VOH) and Lewis acid sites (V). Surface relaxations have no influence on ammonia adsorption on saturated (001) surface, while a strong dependence on the relaxation models is observed for NH3-adsorption energies on (010) and (100) surfaces, especially at the Lewis acid sites of both side planes. When complete relaxation considered (F-model), ammonia adsorption on the Lewis acid sites (V) dominates for side planes (010) and (100). In the presence of VOH as neighbor, the ammonia adsorption at V sites is however weakened significantly due to steric hindrance. Hydrogen bonds may play a role, although not determining one, in the respect of the adsorption of ammonia on (010) and (100) surfaces. Moderate relaxation and full relaxation are absolutely necessary for the description of both H and NH3 adsorption on unsaturated (100) and (010) surfaces, respectively.

Cryogenic adsorption of nitrogen on activated carbon: Experiment and modeling

NASA Astrophysics Data System (ADS)

Zou, Long-Hui; Liu, Hui-Ming; Gong, Ling-Hui

2018-03-01

A cryo-sorption device was built based on a commercial gas sorption analyzer with its sample chamber connected to the 2nd stage of the Gifford-McMahon (GM) cryocooler (by SUMITOMO Corporation), which could provide the operation temperature ranging from 4.5 K to 300 K; The nitrogen adsorption isotherms ranging from 95 to 160 K were obtained by volumetric method on the PICATIF activated carbon. Isosteric heat of adsorption was calculated using the Clausius-Clapeyron equation and was around 8 kJ/mol. Conventional isotherm models and the artificial neural network (ANN) were applied to analyze the adsorption data, the Dual-site Langmuir and the Toth equation turned out to be the most suitable empirical isotherm model; Adsorption equilibrium data at some temperature was used to train the neural network and the rest was used to validate and predict, it turned out that the accuracy of the prediction by the ANN increased with increasing hidden-layer, and it was within ±5% for the three-hidden-layer ANN, and it showed better performance than the conventional isotherm model; Considering large time consumption and complexity of the adsorption experiment, the ANN method can be applied to get more adsorption data based on the already known experimental data.

Adsorption of diclofenac and nimesulide on activated carbon: Statistical physics modeling and effect of adsorbate size

NASA Astrophysics Data System (ADS)

Sellaoui, Lotfi; Mechi, Nesrine; Lima, Éder Cláudio; Dotto, Guilherme Luiz; Ben Lamine, Abdelmottaleb

2017-10-01

Based on statistical physics elements, the equilibrium adsorption of diclofenac (DFC) and nimesulide (NM) on activated carbon was analyzed by a multilayer model with saturation. The paper aimed to describe experimentally and theoretically the adsorption process and study the effect of adsorbate size using the model parameters. From numerical simulation, the number of molecules per site showed that the adsorbate molecules (DFC and NM) were mostly anchored in both sides of the pore walls. The receptor sites density increase suggested that additional sites appeared during the process, to participate in DFC and NM adsorption. The description of the adsorption energy behavior indicated that the process was physisorption. Finally, by a model parameters correlation, the size effect of the adsorbate was deduced indicating that the molecule dimension has a negligible effect on the DFC and NM adsorption.

Adsorption of pharmaceuticals onto trimethylsilylated mesoporous SBA-15.

PubMed

Bui, Tung Xuan; Pham, Viet Hung; Le, Son Thanh; Choi, Heechul

2013-06-15

The adsorption of a complex mixture of 12 selected pharmaceuticals to trimethylsilylated mesoporous SBA-15 (TMS-SBA-15) has been investigated by batch adsorption experiments. The adsorption of pharmaceuticals to TMS-SBA-15 was highly dependent on the solution pH and pharmaceutical properties (i.e., hydrophobicity (logKow) and acidity (pKa)). Good log-log linear relationships between the adsorption (Kd) and pH-dependent octanol-water coefficients (Kow(pH)) were then established among the neutral, anionic, and cationic compounds, suggesting hydrophobic interaction as a primary driving force in the adsorption. In addition, the neutral species of each compound accounted for a major contribution to the overall compound adsorption onto TMS-SBA-15. The adsorption kinetics of pharmaceuticals was evaluated by the nonlinear first-order and pseudo-second-order models. The first-order model gave a better fit for five pharmaceuticals with lower adsorption capacity, whereas the pseudo-second-order model fitted better for seven pharmaceuticals having higher adsorption capacity. In the same group of properties, pharmaceuticals having higher adsorption capacity exhibited faster adsorption rates. The rate-limiting steps for adsorption of pharmaceuticals onto TMS-SBA-15 are boundary layer diffusion and intraparticle diffusion including diffusion in mesopores and micropores. In addition, the adsorption of pharmaceuticals to TMS-SBA-15 was not influenced by the change of initial pharmaceutical concentration (10-100μgL(-1)) and the presence of natural organic matter. Copyright © 2013 Elsevier B.V. All rights reserved.

Factors influencing antibiotics adsorption onto engineered adsorbents.

PubMed

Xia, Mingfang; Li, Aimin; Zhu, Zhaolian; Zhou, Qin; Yang, Weiben

2013-07-01

The study evaluated the adsorption of two antibiotics by four engineered adsorbents (hypercrosslinked resin MN-202, macroporous resin XAD-4, activated carbon F-400, and multi-walled carbon nanotubes (MWCNT)) from aqueous solutions. The dynamic results demonstrated the dominant influence of pore size in adsorption. The adsorption amounts of antibiotics on XAD-4 were attributed to the hydrophobic effect, whereas steric hindrance or micropore-filling played a main role in the adsorption of antibiotics by F-400 because of its high microporosity. Aside from F-400, similar patterns of pH-dependent adsorption were observed, implying the importance of antibiotic molecular forms to the adsorption process for adsorbents. Increasing the ionic concentration with CaC12 produced particular adsorption characteristics on MWCNT at pH 2.0 and F-400 at pH 8.0, which were attributed to the highly available contact surfaces and molecular sieving, respectively. Its hybrid characteristics incorporating a considerable portion of mesopores and micropores made hypercross linked MN-202 a superior antibiotic adsorbent with high adsorption capacity. Furthermore, the adsorption capacity of MWCNT on the basis of surface area was more advantageous than that of the other adsorbents because MWCNT has a much more compact molecular arrangement.

Adsorption energies and prefactor determination for CH3OH adsorption on graphite.

PubMed

Doronin, M; Bertin, M; Michaut, X; Philippe, L; Fillion, J-H

2015-08-28

In this paper, we have studied adsorption and thermal desorption of methanol CH3OH on graphite surface, with the specific aim to derive from experimental data quantitative parameters that govern the desorption, namely, adsorption energy Eads and prefactor ν of the Polanyi-Wigner law. In low coverage regime, these two values are interconnected and usually the experiments can be reproduced with any couple (Eads, ν), which makes intercomparison between studies difficult since the results depend on the extraction method. Here, we use a method for determining independently the average adsorption energy and a prefactor value that works over a large range of incident methanol coverage, from a limited set of desorption curves performed at different heating rates. In the low coverage regime the procedure is based on a first order kinetic law, and considers an adsorption energy distribution which is not expected to vary with the applied heating rate. In the case of CH3OH multilayers, Eads is determined as 430 meV with a prefactor of 5 × 10(14) s(-1). For CH3OH submonolayers on graphite, adsorption energy of 470 ± 30 meV and a prefactor of (8 ± 3) × 10(16) s(-1) have been found. These last values, which do not change between 0.09 ML and 1 ML initial coverage, suggest that the methanol molecules form island-like structure on the graphite even at low coverage.

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

Competitive adsorption of textile dyes using peat: adsorption equilibrium and kinetic studies in monosolute and bisolute systems.

PubMed

Sepulveda, L; Troncoso, F; Contreras, E; Palma, C

2008-09-01

The purpose of this study is to investigate the adsorption by peat of four reactive textile dyes with the following commercial names: Yellow CIBA WR 200% (Y), Dark Blue CIBA WR (DB), Navy CIBA WB (N), and Red CIBA WB 150% (R), used in a cotton-polyester fabric finishing plant. The decolorization levels obtained varied between 5% and 30%, and the most significant variables were pH and ionic strength. Equilibrium studies were carried out at pH 2.8 and temperature of 25 degrees C. Maximum adsorption capacities were between 15 and 20 mg g(-1). Experimental data were fitted to the models of Langmuir. The equilibrium studies for bisolute systems were DB-R and Y-N mixtures. The Langmuir extended model indicated that there is competition for adsorption sites and without interaction between dyes. The results of the kinetic adsorption studies on monosolute and bisolute systems were fitted to the film-pore diffusion, variable diffusivity and quasi-stationary models. They showed that the diffusivity coefficients obtained varied between 2.0 x 10(-8) and 8.5 x 10(-8) cm2s(-1) when the variable diffusivity mass transfer model (VDM) was used and effective diffusion coefficient was fitted between 3.3 x 10(-7) and 56.0 x 10(-7) cm2s(-1) for the film-pore diffusion model (FPDM). The root of average of squares relative error obtained varied between 0.8% and 47.0% for the VDM and FPDM models, respectively.

Kinetics of Molybdenum Adsorption and Desorption in Soils.

PubMed

Sun, Wenguang; Selim, H Magdi

2018-05-01

Much uncertainty exists in mechanisms and kinetics controlling the adsorption and desorption of molybdenum (Mo) in the soil environment. To investigate the characteristics of Mo adsorption and desorption and predict Mo behavior in the vadose zone, kinetic batch experiments were performed using three soils: Webster loam, Windsor sand and Mahan sand. Adsorption isotherms for Mo were strongly nonlinear for all three soils. Strong kinetic adsorption of Mo by all soils was also observed, where the rate of retention was rapid initially and was followed by slow retention behavior with time. The time-dependent Mo sorption rate was not influenced when constant pH was maintained. Desorption or release results indicated that there were significant fractions of Mo that appeared to be irreversible or slowly reversibly sorbed by Windsor and Mahan. X-ray absorption near edge structure (XANES) analysis for Windsor and Mahan soils indicated that most of Mo had been bound to kaolinite, whereas Webster had similar XANES features to those of Mo sorbed to montmorillonite. A sequential extraction procedure provided evidence that a significant amount of Mo was irreversibly sorbed. A multireaction model (MRM) with nonlinear equilibrium and kinetic sorption parameters was used to describe the adsorption-desorption kinetics of Mo on soils. Our results demonstrated that a formulation of MRM with two sorption sites (equilibrium and reversible) successfully described Mo adsorption-desorption data for Webster loam, and an additional irreversible reaction phase was recommended to describe Mo desorption or release with time for Windsor and Mahan soils. Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.

On the Adsorption of DNA Origami Nanostructures in Nanohole Arrays.

PubMed

Brassat, Katharina; Ramakrishnan, Saminathan; Bürger, Julius; Hanke, Marcel; Doostdar, Mahnaz; Lindner, Jörg K N; Grundmeier, Guido; Keller, Adrian

2018-05-22

DNA origami nanostructures are versatile substrates for the controlled arrangement of molecular capture sites with nanometer precision and thus have many promising applications in single-molecule bioanalysis. Here, we investigate the adsorption of DNA origami nanostructures in nanohole arrays which represent an important class of biosensors and may benefit from the incorporation of DNA origami-based molecular probes. Nanoholes with well-defined diameter that enable the adsorption of single DNA origami triangles are fabricated in Au films on Si wafers by nanosphere lithography. The efficiency of directed DNA origami adsorption on the exposed SiO 2 areas at the bottoms of the nanoholes is evaluated in dependence of various parameters, i.e., Mg 2+ and DNA origami concentrations, buffer strength, adsorption time, and nanohole diameter. We observe that the buffer strength has a surprisingly strong effect on DNA origami adsorption in the nanoholes and that multiple DNA origami triangles with 120 nm edge length can adsorb in nanoholes as small as 120 nm in diameter. We attribute the latter observation to the low lateral mobility of once adsorbed DNA origami on the SiO 2 surface, in combination with parasitic adsorption to the Au film. Although parasitic adsorption can be suppressed by modifying the Au film with a hydrophobic self-assembled monolayer, the limited surface mobility of the adsorbed DNA origami still leads to poor localization accuracy in the nanoholes and results in many DNA origami crossing the boundary to the Au film even under optimized conditions. We discuss possible ways to minimize this effect by varying the composition of the adsorption buffer, employing different fabrication conditions, or using other substrate materials for nanohole array fabrication.

Isosteric heat of hydrogen adsorption on MOFs: comparison between adsorption calorimetry, sorption isosteric method, and analytical models

NASA Astrophysics Data System (ADS)

Kloutse, A. F.; Zacharia, R.; Cossement, D.; Chahine, R.; Balderas-Xicohténcatl, R.; Oh, H.; Streppel, B.; Schlichtenmayer, M.; Hirscher, M.

2015-12-01

Isosteric heat of adsorption is an important parameter required to describe the thermal performance of adsorptive storage systems. It is most frequently calculated from adsorption isotherms measured over wide ranges of pressure and temperature, using the so-called adsorption isosteric method. Direct quantitative estimation of isosteric heats on the other hand is possible using the coupled calorimetric-volumetric method, which involves simultaneous measurement of heat and adsorption. In this work, we compare the isosteric heats of hydrogen adsorption on microporous materials measured by both methods. Furthermore, the experimental data are compared with the isosteric heats obtained using the modified Dubinin-Astakhov, Tóth, and Unilan adsorption analytical models to establish the reliability and limitations of simpler methods and assumptions. To this end, we measure the hydrogen isosteric heats on five prototypical metal-organic frameworks: MOF-5, Cu-BTC, Fe-BTC, MIL-53, and MOF-177 using both experimental methods. For all MOFs, we find a very good agreement between the isosteric heats measured using the calorimetric and isosteric methods throughout the range of loading studied. Models' prediction on the other hand deviates from both experiments depending on the MOF studied and the range of loading. Under low-loadings of less than 5 mol kg-1, the isosteric heat of hydrogen adsorption decreases in the order Cu-BTC > MIL-53 > MOF-5 > Fe-BTC > MOF-177. The order of isosteric heats is coherent with the strength of hydrogen interaction revealed from previous thermal desorption spectroscopy measurements.

The Correlation of Adsorption Behavior between Ciprofloxacin Hydrochloride and the Active Sites of Fe-doped MCM-41.

PubMed

Wu, Ying; Tang, Yiming; Li, Laisheng; Liu, Peihong; Li, Xukai; Chen, Weirui; Xue, Ying

2018-01-01

HIGHLIGHTS Fe incorporation significantly accelerated the adsorption of CPX on MCM-41.Fe leaching can be ignored when pH was higher than 4.0.pH played an important role in CPX adsorption on Fe-MCM-41.Co-effect of CPX and metal cations on Fe-MCM-41 was investigated. Fe-MCM-41s with various molar ratios of silicon to iron (20, 40, 80, and 160) were prepared to investigate adsorption properties of ciprofloxacin hydrochloride (CPX) in aqueous solutions. Fe-MCM-41s were characterized by transmission electron microscope (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption/desorption isotherms, and infrared spectroscopy (FT-IR). Effects of silicon-iron ratio, adsorbent dosage, pH, and temperature were conducted to explore the adsorption mechanism of CPX on Fe-MCM-41. The results showed that the introduction of iron facilitated the absorption quantity for CPX from 20.04 to 83.33 mg g -1 at 120 min of reaction time, which was mainly attributed to surface complexation. The promotion of hydrophobic effect, electrostatic interactions, and π-π electron donor-acceptor interaction also played coordinate roles in the adsorption process. The experimental kinetic data followed both the pseudo-second-order and intra-particle diffusion models, while the adsorption isotherm data fit well to Freundlich model at high temperature. Thermodynamic study showed that the adsorption was spontaneous. Under the effect of electrostatic interaction, pH of the solution strongly affected CPX adsorption. Five representative metal cations (Ca, Cu, Ni, Pb, and Cd) were chosen to study the effects on CPX adsorption and their complexation. The inhibiting effect of metal cations on CPX adsorption was sequenced in the order of Cu > Ni > Pb > Cd > Ca, which followed the same order as the complexation stability constants between CPX and cations. The Fe-MCM-41 adsorbent possessed excellent reusability for 4 cycles use, suggesting a potential applicability of Fe-MCM-41

The Correlation of Adsorption Behavior between Ciprofloxacin Hydrochloride and the Active Sites of Fe-doped MCM-41

PubMed Central

Wu, Ying; Tang, Yiming; Li, Laisheng; Liu, Peihong; Li, Xukai; Chen, Weirui; Xue, Ying

2018-01-01

HIGHLIGHTS Fe incorporation significantly accelerated the adsorption of CPX on MCM-41.Fe leaching can be ignored when pH was higher than 4.0.pH played an important role in CPX adsorption on Fe-MCM-41.Co-effect of CPX and metal cations on Fe-MCM-41 was investigated. Fe-MCM-41s with various molar ratios of silicon to iron (20, 40, 80, and 160) were prepared to investigate adsorption properties of ciprofloxacin hydrochloride (CPX) in aqueous solutions. Fe-MCM-41s were characterized by transmission electron microscope (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption/desorption isotherms, and infrared spectroscopy (FT-IR). Effects of silicon-iron ratio, adsorbent dosage, pH, and temperature were conducted to explore the adsorption mechanism of CPX on Fe-MCM-41. The results showed that the introduction of iron facilitated the absorption quantity for CPX from 20.04 to 83.33 mg g−1 at 120 min of reaction time, which was mainly attributed to surface complexation. The promotion of hydrophobic effect, electrostatic interactions, and π-π electron donor-acceptor interaction also played coordinate roles in the adsorption process. The experimental kinetic data followed both the pseudo-second-order and intra-particle diffusion models, while the adsorption isotherm data fit well to Freundlich model at high temperature. Thermodynamic study showed that the adsorption was spontaneous. Under the effect of electrostatic interaction, pH of the solution strongly affected CPX adsorption. Five representative metal cations (Ca, Cu, Ni, Pb, and Cd) were chosen to study the effects on CPX adsorption and their complexation. The inhibiting effect of metal cations on CPX adsorption was sequenced in the order of Cu > Ni > Pb > Cd > Ca, which followed the same order as the complexation stability constants between CPX and cations. The Fe-MCM-41 adsorbent possessed excellent reusability for 4 cycles use, suggesting a potential applicability of Fe-MCM-41

Gas adsorption capacity in an all carbon nanomaterial composed of carbon nanohorns and vertically aligned carbon nanotubes.

PubMed

Puthusseri, Divya; Babu, Deepu J; Okeil, Sherif; Schneider, Jörg J

2017-10-04

Whereas vertically aligned carbon nanotubes (VACNTs) typically show a promising adsorption behavior at high pressures, carbon nanohorns (CNHs) exhibit superior gas adsorption properties in the low pressure regime due to their inherent microporosity. These adsorption characteristics are further enhanced when both materials are opened at their tips. The so prepared composite material allows one to investigate the effect of physical entrapment of CO 2 molecules within the specific adsorption sites of VACNTs composed of opened double walled carbon nanotubes (CNTs) and in specific adsorption sites created by spherically aggregated opened single walled carbon nanohorns. Combining 50 wt% of tip opened CNTs with tip opened CNHs increases the CO 2 adsorption capacity of this material by ∼24% at 30 bar and 298 K compared to opened CNHs alone.

Adsorption and Conformation Change of Helical Peptides on Colloidal Silica

NASA Astrophysics Data System (ADS)

Read, Michael; Zhang, Shuguang; Mayes, Anne; Burkett, Sandra

2001-03-01

Helical conformations of short peptides in solution are partly stabilized by the pattern of electrostatic charge formed by the amino acid sequence. We have studied the role of electrostatics in the adsorption and helix-coil transition of peptides on oxide surfaces. Adsorption isotherms, along with a combination of spectroscopic techniques, show that this is a reversible equilibrium process. Strong electrostatic forces between ionic side chains and charged surface sites increase the adsorbed amount, and promote a loss of helicity in the adsorbed state qualitatively different from that observed upon thermal or chemical perturbation. The electrical dipole of the peptide, arising from the amino acid side chains, serves to orient the molecules on the surface. Effects of adsorption, orientation, and conformation change on the activity of peptides in model biological reactions, as well as the relevance of this simplified system to protein adsorption, are considered.

Selective adsorption of a supramolecular structure on flat and stepped gold surfaces

NASA Astrophysics Data System (ADS)

Peköz, Rengin; Donadio, Davide

2018-04-01

Halogenated aromatic molecules assemble on surfaces forming both hydrogen and halogen bonds. Even though these systems have been intensively studied on flat metal surfaces, high-index vicinal surfaces remain challenging, as they may induce complex adsorbate structures. The adsorption of 2,6-dibromoanthraquinone (2,6-DBAQ) on flat and stepped gold surfaces is studied by means of van der Waals corrected density functional theory. Equilibrium geometries and corresponding adsorption energies are systematically investigated for various different adsorption configurations. It is shown that bridge sites and step edges are the preferred adsorption sites for single molecules on flat and stepped surfaces, respectively. The role of van der Waals interactions, halogen bonds and hydrogen bonds are explored for a monolayer coverage of 2,6-DBAQ molecules, revealing that molecular flexibility and intermolecular interactions stabilize two-dimensional networks on both flat and stepped surfaces. Our results provide a rationale for experimental observation of molecular carpeting on high-index vicinal surfaces of transition metals.

Adsorption behavior of acetone solvent at the HMX crystal faces: A molecular dynamics study.

PubMed

Liu, Yingzhe; Yu, Tao; Lai, Weipeng; Ma, Yiding; Kang, Ying; Ge, Zhongxue

2017-06-01

Molecular dynamics simulations have been performed to understand the adsorption behavior of acetone (AC) solvent at the three surfaces of 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctan (HMX) crystal, i.e. (011), (110), and (020) faces. The simulation results show that the structural features and electrostatic potentials of crystal faces are determined by the HMX molecular packing, inducing distinct mass density distribution, dipole orientation, and diffusion of solvent molecules in the interfacial regions. The solvent adsorption is mainly governed by the van der Waals forces, and the crystal-solvent interaction energies among three systems are ranked as (020)≈(110)>(011). The adsorption sites for solvent incorporation at the crystal surface were found and visualized with the aid of occupancy analysis. A uniform arrangement of adsorption sites is observed at the rough (020) surface as a result of ordered adsorption motif. Copyright © 2017 Elsevier Inc. All rights reserved.

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

PubMed

Laaksonen, Ari

2015-04-23

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

Multisite adsorption of cadmium on goethite

DOE Office of Scientific and Technical Information (OSTI.GOV)

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

1996-11-10

Recently a new general ion adsorption model has been developed for ion binding to mineral surfaces (Hiemstra and van Riemsdijk, 1996). The model uses the Pauling concept of charge distribution (CD) and is an extension of the multi-site complexation (MUSIC) approach. In the CD-MUSIC model the charge of an adsorbing ion that forms an inner sphere complex is distributed over its ligands, which are present in two different electrostatic planes. In this paper the authors have applied the CD-MUSIC model to the adsorption of metal cations, using an extended data set for cadmium adsorbing on goethite. The adsorption of cadmiummore » and the cadmium-proton exchange ratio were measured as function of metal ion concentration, pH, and ionic strength. The data could be described well, taking into account the surface heterogeneity resulting from the presence of two different crystal planes (the dominant 110 face and the minor 021 face). The surface species used in the model are consistent with recent EXAFS data. In accordance with the EXAFS results, high-affinity complexes at the 021 face were used in the model.« less

A relativistic density functional study of the role of 5f electrons in atomic and molecular adsorptions on actinide surfaces

NASA Astrophysics Data System (ADS)

Huda, Muhammad Nurul

Atomic and molecular adsorptions of oxygen and hydrogen on actinide surfaces have been studied within the generalized gradient approximations to density functional theory (GGA-DFT). The primary goal of this work is to understand the details of the adsorption processes, such as chemisorption sites, energies, adsorption configurations and activation energies for dissociation of molecules; and the signature role of the plutonium 5f electrons. The localization of the 5f electrons remains one of central questions in actinides and one objective here is to understand the extent to which localizations plays a role in adsorption on actinide surfaces. We also investigated the magnetism of the plutonium surfaces, given the fact that magnetism in bulk plutonium is a highly controversial issue, and the surface magnetism of it is not a well explored territory. Both the non-spin-polarized and spin-polarized calculations have been performed to arrive at our conclusions. We have studied both the atomic and molecular hydrogen and oxygen adsorptions on plutonium (100) and (111) surfaces. We have also investigated the oxygen molecule adsorptions on uranium (100) surface. Comparing the adsorption on uranium and plutonium (100) surfaces, we have seen that O2 chemisorption energy for the most favorable adsorption site on uranium surface has higher chemisorption energy, 9.492 eV, than the corresponding plutonium site, 8.787 eV. Also degree of localization of 5f electrons is less for uranium surface. In almost all of the cases, the most favorable adsorption sites are found where the coordination numbers are higher. For example, we found center sites are the most favorable sites for atomic adsorptions. In general oxygen reacts more strongly with plutonium surface than hydrogen. We found that atomic oxygen adsorption energy on (100) surface is 3.613 eV more than that of the hydrogen adsorptions, considering only the most favorable site. This is also true for molecular adsorptions, as the

Adsorption Device Based on a Langatate Crystal Microbalance for High Temperature High Pressure Gas Adsorption in Zeolite H-ZSM-5.

PubMed

Ding, Wenjin; Baracchini, Giulia; Klumpp, Michael; Schwieger, Wilhelm; Dittmeyer, Roland

2016-08-25

We present a high-temperature and high-pressure gas adsorption measurement device based on a high-frequency oscillating microbalance (5 MHz langatate crystal microbalance, LCM) and its use for gas adsorption measurements in zeolite H-ZSM-5. Prior to the adsorption measurements, zeolite H-ZSM-5 crystals were synthesized on the gold electrode in the center of the LCM, without covering the connection points of the gold electrodes to the oscillator, by the steam-assisted crystallization (SAC) method, so that the zeolite crystals remain attached to the oscillating microbalance while keeping good electroconductivity of the LCM during the adsorption measurements. Compared to a conventional quartz crystal microbalance (QCM) which is limited to temperatures below 80 °C, the LCM can realize the adsorption measurements in principle at temperatures as high as 200-300 °C (i.e., at or close to the reaction temperature of the target application of one-stage DME synthesis from the synthesis gas), owing to the absence of crystalline-phase transitions up to its melting point (1,470 °C). The system was applied to investigate the adsorption of CO2, H2O, methanol and dimethyl ether (DME), each in the gas phase, on zeolite H-ZSM-5 in the temperature and pressure range of 50-150 °C and 0-18 bar, respectively. The results showed that the adsorption isotherms of these gases in H-ZSM-5 can be well fitted by Langmuir-type adsorption isotherms. Furthermore, the determined adsorption parameters, i.e., adsorption capacities, adsorption enthalpies, and adsorption entropies, compare well to literature data. In this work, the results for CO2 are shown as an example.

Adsorption Device Based on a Langatate Crystal Microbalance for High Temperature High Pressure Gas Adsorption in Zeolite H-ZSM-5

PubMed Central

Ding, Wenjin; Baracchini, Giulia; Klumpp, Michael; Schwieger, Wilhelm; Dittmeyer, Roland

2016-01-01

We present a high-temperature and high-pressure gas adsorption measurement device based on a high-frequency oscillating microbalance (5 MHz langatate crystal microbalance, LCM) and its use for gas adsorption measurements in zeolite H-ZSM-5. Prior to the adsorption measurements, zeolite H-ZSM-5 crystals were synthesized on the gold electrode in the center of the LCM, without covering the connection points of the gold electrodes to the oscillator, by the steam-assisted crystallization (SAC) method, so that the zeolite crystals remain attached to the oscillating microbalance while keeping good electroconductivity of the LCM during the adsorption measurements. Compared to a conventional quartz crystal microbalance (QCM) which is limited to temperatures below 80 °C, the LCM can realize the adsorption measurements in principle at temperatures as high as 200-300 °C (i.e., at or close to the reaction temperature of the target application of one-stage DME synthesis from the synthesis gas), owing to the absence of crystalline-phase transitions up to its melting point (1,470 °C). The system was applied to investigate the adsorption of CO2, H2O, methanol and dimethyl ether (DME), each in the gas phase, on zeolite H-ZSM-5 in the temperature and pressure range of 50-150 °C and 0-18 bar, respectively. The results showed that the adsorption isotherms of these gases in H-ZSM-5 can be well fitted by Langmuir-type adsorption isotherms. Furthermore, the determined adsorption parameters, i.e., adsorption capacities, adsorption enthalpies, and adsorption entropies, compare well to literature data. In this work, the results for CO2 are shown as an example. PMID:27585356

Adsorption and mineralization of REE-lanthanum onto bacterial cell surface.

PubMed

Cheng, Yangjian; Zhang, Li; Bian, Xiaojing; Zuo, Hongyang; Dong, Hailiang

2017-07-11

A large number of rare earth element mining and application resulted in a series of problems of soil and water pollution. Environmental remediation of these REE-contaminated sites has become a top priority. This paper explores the use of Bacillus licheniformis to adsorb lanthanum and subsequent mineralization process in contaminated water. The maximum adsorption capacity of lanthanum on bacteria was 113.98 mg/g (dry weight) biomass. X-ray diffraction (XRD) and transmission electron microscopy (TEM) data indicated that adsorbed lanthanum on bacterial cell surface occurred in an amorphous form at the initial stage. Scanning electron microscopy with X-ray energy-dispersive spectroscopy (SEM/EDS) results indicated that lanthanum adsorption was correlated with phosphate. The amorphous material was converted into scorpion-like monazite (LaPO 4 nanoparticles) in a month. The above results provide a method of using bacterial surface as adsorption and nucleation sites to treat REE-contaminated water.

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.

Adsorption and desorption of arsenic to aquifer sediment on the Red River floodplain at Nam Du, Vietnam

PubMed Central

Thi Hoa Mai, Nguyen; Postma, Dieke; Thi Kim Trang, Pham; Jessen, Søren; Hung Viet, Pham; Larsen, Flemming

2016-01-01

The adsorption of arsenic onto aquifer sediment from the Red River floodplain, Vietnam, was determined in a series of batch experiments. Due to water supply pumping, river water infiltrates into the aquifer at the field site and has leached the uppermost aquifer sediments. The leached sediments, remain anoxic but contain little reactive arsenic and iron, and are used in our experiments. The adsorption and desorption experiments were carried out by addition or removal of arsenic from the aqueous phase in sediment suspensions under strictly anoxic conditions. Also the effects of HCO3, Fe(II), PO4 and Si on arsenic adsorption were explored. The results show much stronger adsorption of As(V) as compared to As(III), full reversibility for As(III) adsorption and less so for As(V). The presence or absence of HCO3 did not influence arsenic adsorption. Fe(II) enhanced As(V) sorption but did not influence the adsorption of As(III) in any way. During simultaneous adsorption of As(III) and Fe(II), As(III) was found to be fully desorbable while Fe(II) was completely irreversibly adsorbed and clearly the two sorption processes are uncoupled. Phosphate was the only solute that significantly could displace As(III) from the sediment surface. Compiling literature data on arsenic adsorption to aquifer sediment in Vietnam and Bangladesh revealed As(III) isotherms to be almost identical regardless of the nature of the sediment or the site of sampling. In contrast, there was a large variation in As(V) adsorption isotherms between studies. A tentative conclusion is that As(III) and As(V) are not adsorbing onto the same sediment surface sites. The adsorption behavior of arsenic onto aquifer sediments and synthetic Fe-oxides is compared. Particularly, the much stronger adsorption of As(V) than of As(III) onto Red River as well as on most Bangladesh aquifer sediments, indicates that the perception that arsenic, phosphate and other species compete for the same surface sites of iron oxides in

Theoretical insights into the uranyl adsorption behavior on vanadium carbide MXene

NASA Astrophysics Data System (ADS)

Zhang, Yu-Juan; Zhou, Zhang-Jian; Lan, Jian-Hui; Ge, Chang-Chun; Chai, Zhi-Fang; Zhang, Peihong; Shi, Wei-Qun

2017-12-01

Remediation of the contamination by long-lived actinide wastes is extremely important but also challenging. Adsorption based techniques have attracted much research attention for their potential as low-cost and effective methods to reduce the radioactive waste from solution. In this work, we have investigated the adsorption behavior of uranyl species [with the general form UO2(L1)x(L2)y(L3)z, where L1, L2 and L3 stand for ligands H2O, OH and CO3, respectively] on hydroxylated vanadium carbide V2C(OH)2 MXene nanosheets using density functional theory based simulation methods We find that all studied uranyl species can stably bond to hydroxylated MXene with binding energies ranging from -3.3 to -4.6 eV, suggesting that MXenes could be effective adsorbers for uranyl ions. The strong adsorption is achieved by forming two Usbnd O bonds with the hydroxylated Mxene. In addition, the axial oxygen atoms from the uranyl ions form hydrogen bonds with the hydroxylated V2C, further strengthening the adsorption. We have also investigated the effects of F termination on the uranyl adsorption properties of V2C nanosheets. Usbnd F bonds are in general weaker than Usbnd O bonds on the adsorption site, suggesting that F terminated Mexne is less favorable for uranyl adsorption applications.

Features of the adsorption of naproxen enantiomers on weak chiral anion-exchangers in nonlinear chromatography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Asnin, Leonid; Kaczmarski, Krzysztof; Guiochon, Georges A

The retention mechanism of the enantiomers of naproxen on a Pirkle-type chiral stationary phase (CSP) was studied. This CSP is made of a porous silica grafted with quinidine carbamate. It can interact with the weak organic electrolyte naproxen either by adsorbing it or by ion-exchange. Using frontal chromatography, we explored the adsorption equilibrium under such experimental conditions that naproxen dissociates or cannot dissociate. Under conditions preventing ionic dissociation, the adsorption isotherms were measured, the adsorption energy distributions determined, and the chromatographic profiles calculated. Three different types of the adsorption sites were found for both enantiomers. The density and the bindingmore » energy of these sites depend on the nature of the organic modifier. Different solute species, anions, neutral molecules, solvent-ion associates, and solute dimers can coexist in solution, giving rise to different forms of adsorption. This study showed the unexpected occurrence of secondary steps in the breakthrough profiles of S-naproxen in the adsorption mode at high concentrations. Being enantioselective, this phenomenon was assumed to result from the association of solute molecules involving a chiral selector moiety. A multisite Langmuir adsorption model was used to calculate band profiles. Although this model accounts excellently for the experimental adsorption isotherms, it does not explain all the features of the breakthrough profiles. A comparison between the calculated and experimental profiles allowed useful conclusions concerning the effects of the adsorbate-adsorbate and adsorbate-solvent interactions on the adsorption mechanism.« less

Kinetics of tetracycline, oxytetracycline, and chlortetracycline adsorption and desorption on two acid soils.

PubMed

Fernández-Calviño, David; Bermúdez-Couso, Alipio; Arias-Estévez, Manuel; Nóvoa-Muñoz, Juan Carlos; Fernández-Sanjurjo, Maria J; Álvarez-Rodríguez, Esperanza; Núñez-Delgado, Avelino

2015-01-01

The purpose of this work was to quantify retention/release of tetracycline, oxytetracycline, and chlortetracycline on two soils, paying attention to sorption kinetics and to implications of the adsorption/desorption processes on transfer of these pollutants to the various environmental compartments. We used the stirred flow chamber (SFC) procedure to achieve this goal. All three antibiotics showed high affinity for both soils, with greater adsorption intensity for soil 1, the one with the highest organic matter and Al and Fe oxides contents. Desorption was always <15%, exhibiting strong hysteresis in the adsorption/desorption processes. Adsorption was adequately modeled using a pseudo first-order equation with just one type of adsorption sites, whereas desorption was better adjusted considering both fast and slow sorption sites. The adsorption maximum (qmax) followed the sequence tetracycline > oxytetracycline > chlortetracycline in soil 1, with similar values for the three antibiotics and the sequence tetracycline > chlortetracycline > oxytetracycline in soil 2. The desorption sequences were oxytetracycline > tetracycline > chlortetracycline in soil 1 and oxytetracycline > chlortetracycline > tetracycline in soil 2. In conclusion, the SFC technique has yielded new kinetic data regarding tetracycline, oxytetracycline, and chlortetracycline adsorption/desorption on soils, indicating that it can be used to shed further light on the retention and transport processes affecting antibiotics on soils and other media, thus increasing knowledge on the behavior and evolution of these pharmaceutical residues in the environment.

Behaviors and kinetics of toluene adsorption-desorption on activated carbons with varying pore structure.

PubMed

Yang, Xi; Yi, Honghong; Tang, Xiaolong; Zhao, Shunzheng; Yang, Zhongyu; Ma, Yueqiang; Feng, Tiecheng; Cui, Xiaoxu

2018-05-01

This work was undertaken to investigate the behaviors and kinetics of toluene adsorption and desorption on activated carbons with varying pore structure. Five kinds of activated carbon from different raw materials were selected. Adsorption isotherms and breakthrough curves for toluene were measured. Langmuir and Freundlich equations were fitted to the equilibrium data, and the Freundlich equation was more suitable for simulating toluene adsorption. The process consisted of monolayer, multilayer and partial active site adsorption types. The effect of the pore structure of the activated carbons on toluene adsorption capacity was investigated. The quasi-first-order model was more suitable for describing the process than the quasi-second-order model. The adsorption data was also modeled by the internal particle diffusion model and it was found that the adsorption process could be divided into three stages. In the external surface adsorption process, the rate depended on the specific surface area. During the particle diffusion stage, pore structure and volume were the main factors affecting adsorption rate. In the final equilibrium stage, the rate was determined by the ratio of meso- and macro-pores to total pore volume. The rate over the whole adsorption process was dominated by the toluene concentration. The desorption behavior of toluene on activated carbons was investigated, and the process was divided into heat and mass transfer parts corresponding to emission and diffusion mechanisms, respectively. Physical adsorption played the main role during the adsorption process. Copyright © 2017. Published by Elsevier B.V.

Study of carbon dioxide adsorption on a Cu-nitroprusside polymorph

DOE PAGES

Roque-Malherbe, R.; Lozano, C.; Polanco, R.; ...

2011-03-26

A careful structural characterization was carried out to unequivocally determine the structure of the synthesized material. The TGA, DRIFTS and a Pawley fitting of the XRD powder profiles indicate that the hydrated and in situ dehydrated polymorph crystallizes in the orthorhombic space group Pnma. Meanwhile, the CO 2 isosteric heat of adsorption appears to be independent of loading with an average value of 30 kJ/mol. This translates to a physisorption type interaction, where the adsorption energy corresponding to wall and lateral interactions are mutually compensated to produce, an apparently, homogeneous adsorption energy. The somewhat high adsorption energy is probably duemore » to the confinement of the CO 2 molecules in the nitroprusside pores. Statistical Physics and the Dubinin theory for pore volume filling allowed model the CO 2 equilibrium adsorption process in Cu-nitroprusside. A DRIFTS test for the adsorbed CO 2 displayed a peak at about 2338 cm -1 that was assigned to a contribution due to physical adsorption of the molecule. Another peak found at 2362 cm -1 evidenced that this molecule interacts with the Cu 2+, which appears to act as an electron accepting Lewis acid site. In conclusion, the aim of the present paper is to report a Pnma stable Cu-nitroprusside polymorph obtained by the precipitation method that can adsorb carbon dioxide.« less

Ab initio molecular dynamics determination of competitive O 2 vs. N 2 adsorption at open metal sites of M 2 (dobdc)

DOE PAGES

Parkes, Marie V.; Greathouse, Jeffery A.; Hart, David B.; ...

2016-04-04

The separation of oxygen from nitrogen using metal–organic frameworks (MOFs) is of great interest for potential pressure-swing adsorption processes for the generation of purified O 2 on industrial scales. This study uses ab initio molecular dynamics (AIMD) simulations to examine for the first time the pure-gas and competitive gas adsorption of O 2 and N 2 in the M 2(dobdc) (M = Cr, Mn, Fe) MOF series with coordinatively unsaturated metal centers. Effects of metal, temperature, and gas composition are explored. Lastly, this unique application of AIMD allows us to study in detail the adsorption/desorption processes and to visualize themore » process of multiple guests competitively binding to coordinatively unsaturated metal sites of a MOF.« less

Adsorption Characteristics of Bixin on Acid- and Alkali-Treated Kaolinite in Aprotic Solvents

PubMed Central

Rahmalia, Winda; Fabre, Jean-François; Usman, Thamrin

2018-01-01

The adsorption of bixin in aprotic solvents onto acid- and alkali-treated kaolinite was investigated. Kaolinite was treated three times, for 6 h each, with 8 M HCl or 5 M KOH. The adsorbents were characterized by XRD, FT-IR, EDS, and BET-N2. The effects of contact time and dye concentration on adsorption capacity and kinetics, electronic transition of bixin before and after adsorption, and also mechanism of bixin-kaolinite adsorption were investigated. Dye adsorption followed pseudo-second order kinetics and was faster in acetone than in dimethyl carbonate. The best adsorption results were obtained for KOH-treated kaolinite. In both of the solvents, the adsorption isotherm followed the Langmuir model and adsorption capacity was higher in dimethyl carbonate (q m = 0.43 mg/g) than in acetone (0.29 mg/g). The adsorption capacity and kinetics of KOH-treated kaolinite (q m = 0.43 mg/g, k 2 = 3.27 g/mg·min) were better than those of HCl-treated kaolinite (q m = 0.21 mg/g, k 2 = 0.25 g/mg·min) and natural kaolinite (q m = 0.18 mg/g, k 2 = 0.32 g/mg·min). There are shift in the band position of maximum intensity of bixin after adsorption on this adsorbent. Adsorption in this system seemed to be based essentially on chemisorption due to the electrostatic interaction of bixin with the strong basic and reducing sites of kaolinite. PMID:29581720

Use of combined coagulation-adsorption process as pretreatment of landfill leachate

PubMed Central

2013-01-01

Landfill leachate is an important pollution factor resulting from municipal landfill sites. Physical and chemical processes are the better option for pretreatment or full treatment of landfill leachate. This article presents a combination of pre-treatment method (coagulation and adsorption) for leachate collected from municipal solid waste open dumping site. Physico chemical characteristics of stabilized and fresh leachate were examined. Coagulation process was examined by using alum and ferric chloride. A low cost adsorbent, fly ash was used for adsorption studies. Coagulation studies were carried out for fresh and stabilized leachate. Adsorption studies have been conducted for alum pre-treated stabilized leachate. Effect of coagulant dose, adsorbent dose, pH and contact time were carried out. The effective optimum coagulant dosages were 0.6 g/L and 0.7 g/L for alum and ferric chloride respectively for stabilized leachate and incase of fresh leachate 0.8 g/L and 0.6 g/L for alum and ferric chloride respectively. For the alum pretreated stabilized leachate, the maximum COD removal is 28% using fly ash adsorbent with equilibrium time of 210 min and optimum dose of 6 g/L. Overall COD removal efficiency of 82% was obtained by coagulation using alum and adsorption using fly ash for stabilized leachate. The results obtained showed that combined coagulation and adsorption process can be used effectively for stabilized leachate treatment. PMID:23517661

Mechanism of tyramine adsorption on Ca-montmorillonite.

PubMed

Chang, Po-Hsiang; Jiang, Wei-Teh; Li, Zhaohui

2018-06-10

Tyramine (TY) adsorption on a Ca-montmorillonite (SAz-2) was investigated with batch experiments and complementary analyses utilizing ultra-high performance liquid chromatography, ion chromatography, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetry (TG). The adsorption reached equilibrium in 8 h, complying with the pseudo-second-order rate equation, and came to an adsorption capacity of 682 mmol kg -1 at pH 6-8.1, utilizing the Langmuir isotherm model. The adsorption of TY and desorption of exchangeable cations exhibited a linear relationship with a slope of 0.9, implying that the adsorption was largely influenced by a cation exchange mechanism. The effective adsorption was further verified by the characteristic TY bands in the FTIR spectra and the signals of mass loss due to TY decomposition in the TG measurements of the clay after adsorption experiments. Intercalation of hydrated TY into the clay interlayer was confirmed by XRD and TG analyses of the heated samples loaded with TY. The adsorption reached only 0.57 cation exchange capacity of the clay which was probably limited by the low charge density of TY as compared to the negative charge density of the clay surface and by the steric effects arising from the hydration of TY that increased its molecular size. Adsorption of TY on montmorillonite can make TY more resistant to thermal decomposition and possibly better preserved in aquatic and soil environments. Copyright © 2018 Elsevier B.V. All rights reserved.

Adsorption of cadmium(II) on waste biomaterial.

PubMed

Baláž, M; Bujňáková, Z; Baláž, P; Zorkovská, A; Danková, Z; Briančin, J

2015-09-15

Significant increase of the adsorption ability of the eggshell biomaterial toward cadmium was observed upon milling, as is evidenced by the value of maximum monolayer adsorption capacity of 329mgg(-1), which is markedly higher than in the case of most "green" sorbents. The main driving force of the adsorption was proven to be the presence of aragonite phase as a consequence of phase transformation from calcite occurring during milling. Cadmium is adsorbed in a non-reversible way, as documented by different techniques (desorption tests, XRD and EDX measurements). The optimum pH for cadmium adsorption was 7. The adsorption process was accompanied by the increase of the value of specific surface area. The course of adsorption has been described by Langmuir, Freundlich and Dubinin-Radushkevich isotherms. The adsorption kinetics was evaluated using three models, among which the best correlation coefficients and the best normalized standard deviation values were achieved for the pseudo-second order model and the intraparticle diffusion model, respectively. Copyright © 2015 Elsevier Inc. All rights reserved.

The correlation of adsorption behavior between ciprofloxacin hydrochloride and the active sites of Fe-doped MCM-41

NASA Astrophysics Data System (ADS)

Wu, Ying; Tang, Yiming; Li, Laisheng; Liu, Peihong; Li, Xukai; Chen, Weirui; Xue, Ying

2018-02-01

Fe-MCM-41s with various molar ratios of silicon to iron (20, 40, 80 and 160) were prepared to investigate adsorption properties of ciprofloxacin hydrochloride (CPX) in aqueous solutions. Fe-MCM-41s were characterized by transmission electron microscope (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption/desorption isotherms and infrared spectroscopy (FT-IR). Effects of silicon–iron ratio, adsorbent dosage, pH and temperature were conducted to explore the adsorption mechanism of CPX on Fe-MCM-41. The results showed that the introduction of iron facilitated the absorption quantity for CPX from 20.04 to 83.33 mg g-1 at 120 min of reaction time, which was mainly attributed to surface complexation. The promotion of hydrophobic effect, electrostatic interactions and π-π electron donor–acceptor interaction also played coordinate roles in the adsorption process. The experimental kinetic data followed both the pseudo-second-order and intra-particle diffusion models, while the adsorption isotherm data fit well to Freundlich model at high temperature. Thermodynamic study showed that the adsorption was spontaneous. Under the effect of electrostatic interaction, pH of the solution strongly affected CPX adsorption. Five representative metal cations (Ca, Cu, Ni, Pb and Cd) were chosen to study the effects on CPX adsorption and their complexation. The inhibiting effect of metal cations on CPX adsorption was sequenced in the order of Cu > Ni > Pb > Cd > Ca, which followed the same order as the complexation stability constants between CPX and cations. The Fe-MCM-41 adsorbent possessed excellent reusability for 4 cycles use, suggesting a potential applicability of Fe-MCM-41 to remove CPX in water.

Effective adsorption of malachite green using magnetic barium phosphate composite from aqueous solution

NASA Astrophysics Data System (ADS)

Zhang, Fan; Wei, Zhong; Zhang, Wanning; Cui, Haiyan

2017-07-01

Magnetic Ba3(PO4)2/Fe3O4-nanoparticle (called BPFN) was prepared, characterized, and developed as a low-cost adsorbent for malachite green (MG) from aqueous solution. Factors such as adsorption temperature, pH of solution, dosage of adsorbent, adsorption kinetics and isotherms were investigated. The maximum adsorption capacity obtained in this work was 1639 mg g- 1 at 45 °C and pH 6. The adsorption process fitted the pseudo-first-order kinetic model and Langmuir isotherm model. Evidences from zeta potential, Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS) data revealed that the adsorption process was driven by electrostatic attraction, the interaction between Lewis base sbnd N(CH3)2 in MG and Lewis acid Ba sites of BPFN. In addition, the BPFN could be easily regenerated by a magnet and the adsorption capacity maintained at 70% after five cycles. The present study suggests that the BPFN had high potential of removing MG from wastewater.

SERS-activating effect of chlorides on borate-stabilized silver nanoparticles: formation of new reduced adsorption sites and induced nanoparticle fusion.

PubMed

Sloufová, Ivana; Sisková, Karolína; Vlcková, Blanka; Stepánek, Josef

2008-04-28

Changes in morphology, surface reactivity and surface-enhancement of Raman scattering induced by modification of borate-stabilized Ag nanoparticles by adsorbed chlorides have been explored using TEM, EDX analysis and SERS spectra of probing adsorbate 2,2'-bipyridine (bpy) excited at 514.5 nm and evaluated by factor analysis. At fractional coverages of the parent Ag nanoparticles by adsorbed chlorides <0.6, the Ag colloid/Cl(-)/bpy systems were found to be constituted by fractal aggregates of Ag nanoparticles fairly uniform in size (10 +/- 2 nm) and SERS spectra of Ag(+)-bpy surface species were detected. The latter result was interpreted in terms of the presence of oxidized Ag(+) and/or Ag(n)(+) adsorption sites, which have been encountered also in systems with the chemically untreated Ag nanoparticles. At chloride coverages >0.6, a fusion of fractal aggregates into the compact aggregates of touching and/or interpenetrating Ag nanoparticles has been observed and found to be accompanied by the formation of another surface species, Ag-bpy, as well as by the increase of the overall SERS enhancement of bpy by factor of 40. The same Ag-bpy surface species has been detected under the strongly reducing conditions of reduction of silver nitrate by sodium borohydride in the presence of bpy. The formation of Ag-bpy is thus interpreted in terms of the stabilization of reduced Ag(0) adsorption sites by adsorbed bpy. The formation of reduced adsorption sites on Ag nanoparticle surfaces at chloride coverages >0.6 is discussed in terms of local changes in the work function of Ag. Finally, the SERS spectral detection of Ag-bpy species is proposed as a tool for probing the presence of reduced Ag(0) adsorption sites in systems with chemically modified Ag nanoparticles.

Influence of surface roughness on cetyltrimethylammonium bromide adsorption from aqueous solution.

PubMed

Wu, Shuqing; Shi, Liu; Garfield, Lucas B; Tabor, Rico F; Striolo, Alberto; Grady, Brian P

2011-05-17

The influence of surface roughness on surfactant adsorption was studied using a quartz crystal microbalance with dissipation (QCM-D). The sensors employed had root-mean-square (R) roughness values of 2.3, 3.1, and 5.8 nm, corresponding to fractal-calculated surface area ratios (actual/nominal) of 1.13, 1.73, and 2.53, respectively. Adsorption isotherms measured at 25 °C showed that adsorbed mass of cetyltrimethylammonium bromide per unit of actual surface area below 0.8 cmc, or above 1.2 cmc, decreases as the surface roughness increases. At the cmc, both the measured adsorbed amount and the measured dissipation increased dramatically on the rougher surfaces. These results are consistent with the presence of impurities, suggesting that roughness exacerbates well-known phenomena reported in the literature of peak impurity-related adsorption at the cmc. The magnitude of the increase, especially in dissipation, suggests that changes in adsorbed amount may not be the only reason for the observed results, as aggregates at the cmc on rougher surfaces are more flexible and likely contain larger amounts of solvent. Differences in adsorption kinetics were also found as a function of surface roughness, with data showing a second, slower adsorption rate after rapid initial adsorption. A two-rate Langmuir model was used to further examine this effect. Although adsorption completes faster on the smoother surfaces, initial adsorption at zero surface coverage is faster on the rougher surfaces, suggesting the presence of more high-energy sites on the rougher surfaces.

Water Adsorption in Porous Metal-Organic Frameworks and Related Materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Furukawa, H; Gandara, F; Zhang, YB

2014-03-19

Water adsorption in porous materials is important for many applications such as dehumidification, thermal batteries, and delivery of drinking water in remote areas. In this study, we have identified three criteria for achieving high performing porous materials for water adsorption. These criteria deal with condensation pressure of water in the pores, uptake capacity, and recyclability and water stability of the material. In search of an excellently performing porous material, we have studied and compared the water adsorption properties of 23 materials, 20 of which are metal organic frameworks (MOFs). Among the MOFs are 10 zirconium(IV) MOFs with a subset ofmore » these, MOF-801-SC (single crystal form), -802, -805, -806, -808, -812, and -841 reported for the first time. MOF-801-P (microcrystalline powder form) was reported earlier and studied here for its water adsorption properties. MOF-812 was only made and structurally characterized but not examined for water adsorption because it is a byproduct of MOF-841 synthesis. All the new zirconium MOFs are made from the Zr6O4(OH)(4)(-CO2)(n) secondary building units (n = 6, 8, 10, or 12) and variously shaped carboxyl organic linkers to make extended porous frameworks. The permanent porosity of all 23 materials was confirmed and their water adsorption measured to reveal that MOF-801-P and MOF-841 are the highest performers based on the three criteria stated above; they are water stable, do not lose capacity after five adsorption/desorption cycles, and are easily regenerated at room temperature. An X-ray single-crystal study and a powder neutron diffraction study reveal the position of the water adsorption sites in MOF-801 and highlight the importance of the intermolecular interaction between adsorbed water molecules within the pores.« less

Water adsorption in porous metal-organic frameworks and related materials.

PubMed

Furukawa, Hiroyasu; Gándara, Felipe; Zhang, Yue-Biao; Jiang, Juncong; Queen, Wendy L; Hudson, Matthew R; Yaghi, Omar M

2014-03-19

Water adsorption in porous materials is important for many applications such as dehumidification, thermal batteries, and delivery of drinking water in remote areas. In this study, we have identified three criteria for achieving high performing porous materials for water adsorption. These criteria deal with condensation pressure of water in the pores, uptake capacity, and recyclability and water stability of the material. In search of an excellently performing porous material, we have studied and compared the water adsorption properties of 23 materials, 20 of which are metal-organic frameworks (MOFs). Among the MOFs are 10 zirconium(IV) MOFs with a subset of these, MOF-801-SC (single crystal form), -802, -805, -806, -808, -812, and -841 reported for the first time. MOF-801-P (microcrystalline powder form) was reported earlier and studied here for its water adsorption properties. MOF-812 was only made and structurally characterized but not examined for water adsorption because it is a byproduct of MOF-841 synthesis. All the new zirconium MOFs are made from the Zr6O4(OH)4(-CO2)n secondary building units (n = 6, 8, 10, or 12) and variously shaped carboxyl organic linkers to make extended porous frameworks. The permanent porosity of all 23 materials was confirmed and their water adsorption measured to reveal that MOF-801-P and MOF-841 are the highest performers based on the three criteria stated above; they are water stable, do not lose capacity after five adsorption/desorption cycles, and are easily regenerated at room temperature. An X-ray single-crystal study and a powder neutron diffraction study reveal the position of the water adsorption sites in MOF-801 and highlight the importance of the intermolecular interaction between adsorbed water molecules within the pores.

Adsorption of guaiacol on Fe (110) and Pd (111) from first principles

NASA Astrophysics Data System (ADS)

Hensley, Alyssa J. R.; Wang, Yong; McEwen, Jean-Sabin

2016-06-01

The catalytic properties of surfaces are highly dependent upon the effect said surfaces have on the geometric and electronic structure of adsorbed reactants, products, and intermediates. It is therefore crucial to have a surface-level understanding of the adsorption of the key species in a reaction in order to design active and selective catalysts. Here, we study the adsorption of guaiacol on Fe (110) and Pd (111) using dispersion-corrected density functional theory calculations as both of these metals are of interest as hydrodeoxygenation catalysts for the conversion of bio-oils to useable biofuels. Both vertical (via the oxygen functional groups) and horizontal (via the aromatic ring) adsorption configurations were examined and the resulting adsorption and molecular distortion energies showed that the vertical sites were only physisorbed while the horizontal sites were chemisorbed on both metal surfaces. A comparison of guaiacol's horizontal adsorption on Fe (110) and Pd (111) showed that guaiacol had a stronger adsorption on Pd (111) while the Fe (110) surface distorted the Csbnd O bonds to a greater degree. Electronic analyses on the horizontal systems showed that the greater adsorption strength for guaiacol on Pd (111) was likely due to the greater charge transfer between the aromatic ring and the surface Pd atoms. Additionally, the greater distortion of the Csbnd O bonds in adsorbed guaiacol on Fe (110) is likely due to the greater degree of interaction between the oxygen and surface Fe atoms. Overall, our results show that the Fe (110) surface has a greater degree of interaction with the functional groups and the Pd (111) surface has a greater degree of interaction with the aromatic ring.

Gas adsorption capacity of wood pellets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yazdanpanah, F.; Sokhansanj, Shahabaddine; Lim, C. Jim

In this paper, temperature-programmed desorption (TPD) analysis was used to measure and analyze the adsorption of off-gases and oxygen by wood pellets during storage. Such information on how these gases interact with the material helps in the understanding of the purging/stripping behavior of off-gases to develop effective ventilation strategies for wood pellets. Steam-exploded pellets showed the lowest carbon dioxide (CO 2) uptake compared to the regular and torrefied pellets. The high CO 2 adsorption capacity of the torrefied pellets could be attributed to their porous structure and therefore greater available surface area. Quantifying the uptake of carbon monoxide by pelletsmore » was challenging due to chemical adsorption, which formed a strong bond between the material and carbon monoxide. The estimated energy of desorption for CO (97.8 kJ/mol) was very high relative to that for CO 2 (7.24 kJ/mol), demonstrating the mechanism of chemical adsorption and physical adsorption for CO and CO 2, respectively. As for oxygen, the strong bonds that formed between the material and oxygen verified the existence of chemical adsorption and formation of an intermediate material.« less

Adsorption of ferrous ions onto montmorillonites

NASA Astrophysics Data System (ADS)

Qin, Dawei; Niu, Xia; Qiao, Min; Liu, Gang; Li, Hongxin; Meng, Zhenxiao

2015-04-01

The adsorption of Fe (II) onto montmorillonites was investigated through initial concentration, contact time, pH and temperature. During the whole adsorption process, the ascorbic acid (Vitamin C) was added as a kind of antioxidant, at the same time, deionized water (after boiling) and nitrogen protection were also used to avoid oxidation. The Fe2+/Fetotal ratio of the iron exists in the Fe-montmorillonites was found more than 95%. Two kinetic models, including pseudo-first-order and pseudo-second-order model, were used to analyze the adsorption process of Fe (II) on montmorillonites. The results of our study showed that adsorption process fitted with pseudo-second-order well. Adsorption isotherms showed that Langmuir model was better than Freundlich model. The thermodynamic parameters ΔG0 and ΔH0 were 3.696 kJ/mol and 6.689 kJ/mol (we just gave the values at 298 K), respectively. The positive values at different temperatures showed that the adsorption process was non-spontaneous and endothermic. The characteristics of materials were determined by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Surface area and porosity analyzer, Thermogravimetric analysis (TGA), Differential scanning calorimeter (DSC) and Zeta potential distribution.

Gas adsorption capacity of wood pellets

DOE PAGES

Yazdanpanah, F.; Sokhansanj, Shahabaddine; Lim, C. Jim; ...

2016-02-03

In this paper, temperature-programmed desorption (TPD) analysis was used to measure and analyze the adsorption of off-gases and oxygen by wood pellets during storage. Such information on how these gases interact with the material helps in the understanding of the purging/stripping behavior of off-gases to develop effective ventilation strategies for wood pellets. Steam-exploded pellets showed the lowest carbon dioxide (CO 2) uptake compared to the regular and torrefied pellets. The high CO 2 adsorption capacity of the torrefied pellets could be attributed to their porous structure and therefore greater available surface area. Quantifying the uptake of carbon monoxide by pelletsmore » was challenging due to chemical adsorption, which formed a strong bond between the material and carbon monoxide. The estimated energy of desorption for CO (97.8 kJ/mol) was very high relative to that for CO 2 (7.24 kJ/mol), demonstrating the mechanism of chemical adsorption and physical adsorption for CO and CO 2, respectively. As for oxygen, the strong bonds that formed between the material and oxygen verified the existence of chemical adsorption and formation of an intermediate material.« less

Adsorption of glyphosate on variable-charge, volcanic ash-derived soils.

PubMed

Cáceres-Jensen, L; Gan, J; Báez, M; Fuentes, R; Escudey, M

2009-01-01

Glyphosate (N-phosphonometylglycine) is widely used due to its broad spectrum of activity and nonselective mode of action. In Chile it is the most used herbicide, but its adsorption behavior in the abundant and widespread variable charge soils is not well understood. In this study, three volcanic ash-derived soils were selected, including Andisols (Nueva Braunau and Diguillin) and Ultisols (Collipulli), to evaluate the adsorption kinetics, equilibrium isotherms, and the effect of pH in glyphosate adsorption. The influence of glyphosate on soil phosphorus retention was also studied. Glyphosate was rapidly and strongly adsorbed on the selected soils, and adsorption isotherms were well described by the Freundlich relationship with strong nonlinearity (n(fads) < 0.5). The n(fads) values were consistently higher than n(fdes) values, suggesting strong hysteresis. Adsorption (K(ads)) increased strongly when pH decreased. The presence of glyphosate (3200 mug mL(-1)) changed the adsorption behavior of phosphate at its maximum adsorption capacity. Andisol soils without the addition of glyphosate had similar mean K(ads) values for Nueva Braunau (5.68) and Diguillin (7.38). Collipulli had a mean K(ads) value of 31.58. During the successive desorption steps, glyphosate at the highest level increased K(ads) values for phosphate in the Andisol soils but had little effect in the Ultisol soil. This different behavior was probably due to the irreversible occupation of some adsorption sites by glyphosate in the Ultisol soil attributed to the dominant Kaolinite mineral. Results from this study suggest that in the two types of volcanic soils, different mechanisms are involved in glyphosate and phosphate adsorption and that long-term use of glyphosate may impose different effects on the retention and availability of phosphorus. Volcanic ash-derived soils have a particular environmental behavior in relation to the retention of organic contaminants, representing an environmental substrate

Effect of hydrophobicity of pharmaceuticals and personal care products for adsorption on activated carbon: Adsorption isotherms, kinetics and mechanism.

PubMed

Kaur, Harkirat; Bansiwal, Amit; Hippargi, Girivyankatesh; Pophali, Girish R

2017-09-11

Adsorption of three pharmaceuticals and personal care products (PPCPs), namely caffeine, ibuprofen and triclosan on commercial powdered activated carbon was examined in aqueous medium. The contaminants were chosen based on their diverse log K ow (octanol-water partition coefficient) viz. - 0.07 for caffeine, 3.97 for ibuprofen and 4.76 for triclosan to examine the role of hydrophobicity on adsorption process. The adsorbent characterisation was achieved using BET surface area, SEM, pore size distribution studies and FTIR. Influence of mass of PAC, contact time, solution pH and initial concentration on adsorption capacity of PAC was studied. Adsorption isotherms and kinetics were applied to establish the mechanism of adsorption. The kinetics followed pseudo-second order with physisorption occurring through particle diffusion. The Freundlich model fitted best among the isotherm models. The adsorption capacity increased in the order CFN < IBU < TCS which correlates with increasing hydrophobicity (log K ow ), molecular weight and decreasing water solubility, respectively. We conclude that micro-pollutant hydrophobicity contributes towards adsorption on activated carbon.

Electrostatic and dispersion interactions during protein adsorption on topographic nanostructures.

PubMed

Elter, Patrick; Lange, Regina; Beck, Ulrich

2011-07-19

Recently, biomaterials research has focused on developing functional implant surfaces with well-defined topographic nanostructures in order to influence protein adsorption and cellular behavior. To enhance our understanding of how proteins interact with such surfaces, we analyze the adsorption of lysozyme on an oppositely charged nanostructure using a computer simulation. We present an algorithm that combines simulated Brownian dynamics with numerical field calculation methods to predict the preferred adsorption sites for arbitrarily shaped substrates. Either proteins can be immobilized at their initial adsorption sites or surface diffusion can be considered. Interactions are analyzed on the basis of Derjaguin-Landau-Verway-Overbeek (DLVO) theory, including electrostatic and London dispersion forces, and numerical solutions are derived using the Poisson-Boltzmann and Hamaker equations. Our calculations show that for a grooved nanostructure (i.e., groove and plateau width 8 nm, height 4 nm), proteins first contact the substrate primarily near convex edges because of better geometric accessibility and increased electric field strengths. Subsequently, molecules migrate by surface diffusion into grooves and concave corners, where short-range dispersion interactions are maximized. In equilibrium, this mechanism leads to an increased surface protein concentration in the grooves, demonstrating that the total amount of protein per surface area can be increased if substrates have concave nanostructures.

The impact of metabolic state on Cd adsorption onto bacterial cells

USGS Publications Warehouse

Johnson, K.J.; Ams, D.A.; Wedel, A.N.; Szymanowski, J.E.S.; Weber, D.L.; Schneegurt, M.A.; Fein, J.B.

2007-01-01

This study examines the effect of bacterial metabolism on the adsorption of Cd onto Gram-positive and Gram-negative bacterial cells. Metabolically active Gram-positive cells adsorbed significantly less Cd than non-metabolizing cells. Gram-negative cells, however, showed no systematic difference in Cd adsorption between metabolizing and non-metabolizing cells. The effect of metabolism on Cd adsorption to Gram-positive cells was likely due to an influx of protons in and around the cell wall from the metabolic proton motive force, promoting competition between Cd and protons for adsorption sites on the cell wall. The relative lack of a metabolic effect on Cd adsorption onto Gram-negative compared to Gram-positive cells suggests that Cd binding in Gram-negative cells is focused in a region of the cell wall that is not reached, or is unaffected by this proton flux. Thermodynamic modeling was used to estimate that proton pumping causes the pH in the cell wall of metabolizing Gram-positive bacteria to decrease from the bulk solution value of 7.0 to approximately 5.7. ?? 2007 The Authors.

Kinetics of heavy metal adsorption and desorption in soil: Developing a unified model based on chemical speciation

NASA Astrophysics Data System (ADS)

Peng, Lanfang; Liu, Paiyu; Feng, Xionghan; Wang, Zimeng; Cheng, Tao; Liang, Yuzhen; Lin, Zhang; Shi, Zhenqing

2018-03-01

Predicting the kinetics of heavy metal adsorption and desorption in soil requires consideration of multiple heterogeneous soil binding sites and variations of reaction chemistry conditions. Although chemical speciation models have been developed for predicting the equilibrium of metal adsorption on soil organic matter (SOM) and important mineral phases (e.g. Fe and Al (hydr)oxides), there is still a lack of modeling tools for predicting the kinetics of metal adsorption and desorption reactions in soil. In this study, we developed a unified model for the kinetics of heavy metal adsorption and desorption in soil based on the equilibrium models WHAM 7 and CD-MUSIC, which specifically consider metal kinetic reactions with multiple binding sites of SOM and soil minerals simultaneously. For each specific binding site, metal adsorption and desorption rate coefficients were constrained by the local equilibrium partition coefficients predicted by WHAM 7 or CD-MUSIC, and, for each metal, the desorption rate coefficients of various binding sites were constrained by their metal binding constants with those sites. The model had only one fitting parameter for each soil binding phase, and all other parameters were derived from WHAM 7 and CD-MUSIC. A stirred-flow method was used to study the kinetics of Cd, Cu, Ni, Pb, and Zn adsorption and desorption in multiple soils under various pH and metal concentrations, and the model successfully reproduced most of the kinetic data. We quantitatively elucidated the significance of different soil components and important soil binding sites during the adsorption and desorption kinetic processes. Our model has provided a theoretical framework to predict metal adsorption and desorption kinetics, which can be further used to predict the dynamic behavior of heavy metals in soil under various natural conditions by coupling other important soil processes.

Tetracycline adsorption on kaolinite: pH, metal cations and humic acid effects.

PubMed

Zhao, Yanping; Geng, Jinju; Wang, Xiaorong; Gu, Xueyuan; Gao, Shixiang

2011-07-01

Contamination of environmental matrixes by human and animal wastes containing antibiotics is a growing health concern. Because tetracycline is one of the most widely-used antibiotics in the world, it is important to understand the factors that influence its mobility in soils. This study investigated the effects of pH, background electrolyte cations (Li(+), Na(+), K(+), Ca(2+) and Mg(2+)), heavy metal Cu(2+) and humic acid (HA) on tetracycline adsorption onto kaolinite. Results showed that tetracycline was greatly adsorbed by kaolinite over pH 3-6, then decreased with the increase of pH, indicating that tetracycline adsorption mainly through ion exchange of cations species and complexation of zwitterions species. In the presence of five types of cations (Li(+), Na(+), K(+), Ca(2+) and Mg(2+)), tetracycline adsorption decreased in accordance with the increasing of atomic radius and valence of metal cations, which suggested that outer-sphere complexes formed between tetracycline and kaolinite, and the existence of competitor ions lead to the decreasing adsorption. The presence of Cu(2+) greatly enhanced the adsorption probably by acting as a bridge ion between tetracycline species and the edge sites of kaolinite. HA also showed a major effect on the adsorption: at pH < 6, the presence of HA increased the adsorption, while the addition of HA showed little effect on tetracycline adsorption at higher pH. The soil environmental conditions, like pH, metal cations and soil organic matter, strongly influence the adsorption behavior of tetracycline onto kaolinite and need to be considered when assessing the environmental toxicity of tetracycline.

Adsorption of phosphate from seawater on calcined MgMn-layered double hydroxides.

PubMed

Chitrakar, Ramesh; Tezuka, Satoko; Sonoda, Akinari; Sakane, Kohji; Ooi, Kenta; Hirotsu, Takahiro

2005-10-01

Adsorptive properties of MgMn-3-300 (MgMn-type layered double hydroxide with Mg/Mn mole ratio of 3, calcined at 300 degrees C) for phosphate were investigated in phosphate-enriched seawater with a concentration of 0.30 mg-P/dm3. It showed the highest phosphate uptake from the seawater among the inorganic adsorbents studied (hydrotalcite, calcined hydrotalcite, activated magnesia, hydrous aluminum oxide, manganese oxide (delta-MnO2)). The phosphate uptake by MgMn-3-300 reached 7.3 mg-P/g at an adsorbent/solution ratio of 0.05 g/2 dm3. The analyses of the uptakes of other constituents (Na+, K+, Ca(+, Cl-, and SO(2-)4) of seawater showed that the adsorbent had a markedly high selectivity for the adsorption of phosphate ions. Effects of initial phosphate concentration, temperature, pH, and salinity on phosphate uptake were investigated in detail by a batch method. The phosphate uptake increased slightly with an increase in the adsorption temperature. The adsorption isotherm followed Freundlich's equation with constants of logK(F)=1.25 and 1/n=0.65, indicating that it could effectively remove phosphate even from a solution of markedly low phosphate concentration as well as with large numbers of coexisting ions. The pH dependence showed a maximum phosphate uptake around pH 8.5. The pH dependence curve suggested that selective phosphate adsorption progresses mainly by the ion exchange of HPO(2-)4. The study on the effect of salinity suggested the presence of two kinds of adsorption sites in the adsorbent: one nonspecific site with weak interaction and one specific site with strong interaction. The effective desorption of phosphate could be achieved using a mixed solution of 5 M NaCl + 0.1 M NaOH (1 M = 1 mol/dm3), with negligible dissolution of adsorbent. The adsorbent had high chemical stability against the adsorption/desorption cycle; it kept a good phosphate uptake even after the repetition of the seventh cycle.

Adsorption of goethite onto quartz and kaolinite

USGS Publications Warehouse

Goldberg, M.C.; Weiner, Eugene R.; Boymel, P.M.

1984-01-01

The adsorption of colloidal goethite onto quartz and kaolinite substrates has been studied as a function of pH and NaCl concentration. Goethite adsorption was measured quantitatively by Fourier-transform infrared spectroscopy. The results indicate that adsorption onto both substrates is due primarily to coulombic forces; however, the pH dependence of adsorption is very different for the two substrates. This is explained by the fact that the surface charge on quartz is entirely pH-dependent, while kaolinite has surface faces which carry a permanent negative charge. Adsorption of goethite on to kaolinite increases markedly with increasing NaCl concentration, while adsorption onto quartz is relatively independent of NaCl concentration. This can be explained by the influence of NaCl concentration upon the development of surface charge on the substrates. A method is described for separating surface-bound goethite from free goethite.

Effective Adsorption/Reduction of Cr(VI) Oxyanion by Halloysite@Polyaniline Hybrid Nanotubes.

PubMed

Zhou, Tianzhu; Li, Cuiping; Jin, Huiling; Lian, Yangyang; Han, Wenmei

2017-02-22

Halloysite@polyaniline (HA@PANI) hybrid nanotubes are synthesized by the in situ chemical polymerization of aniline on halloysite clay nanotubes. By facilely tuning the dopant acid, pH, and apparent weight proportion for aniline (ANI) and halloysite (HA) nanotubes in the synthesis process, PANI with tuned oxidation state, doping extent, and content are in situ growing on halloysite nanotubes. The reaction system's acidity is tuned by dopant acid, such as HCl, H 2 SO 4 , HNO 3 , and H 3 PO 4 . The adsorption result shows the fabricated HA@PANI hybrid nanotubes can effectively adsorb Cr(VI) oxyanion and the adsorption ability changes according to the dopant acid, pH, and apparent weight proportion for ANI and HA in the synthesis process. Among them, the HA@PANI fabricated with HCl as dopant acid tuning the pH at 0.5 and 204% apparent weight proportion for ANI and HA (HP/0.5/204%-HCl) shows the highest adsorption capacity. The adsorption capacity is in accordance well with the doping extent of PANI in HA@PANI. Furthermore, when HP/0.5/204%-HCl is redoped with HNO 3 , H 2 SO 4 , and H 3 PO 4 , the adsorption capacity declines, implying the dopant acid in the process of redoping exhibits a marked effect on Cr(VI) oxyanion adsorption for the HA@PANI hybrid nanotubes. HP/0.5/204%-HCl and HP/0.5/204%-H 3 PO 4 have demonstrated good regenerability with an above 80% removal ratio after four cycles. Moreover, the HA@PANI adsorbent has better sedimentation ability than that of pure PANI. The adsorption behavior is in good agreement with Langmuir and pseudo second-order equations, indicating the adsorption of HA@PANI for Cr(VI) oxyanion is chemical adsorption. FT-IR and XPS of HA@PANI after Cr(VI) oxyanion adsorption indicate that the doped amine/imine groups (-NH + /═N + - groups) are the main adsorption sites for the removal of Cr(VI) oxyanion by electrostatic adsorption and reduction of the adsorbed Cr (VI) oxyanion to Cr(III) simultaneously.

Hydrothermal Carbonization of Microalgae (Chlorococcum sp.) for Porous Carbons With High Cr(VI) Adsorption Performance.

PubMed

Sun, Yuanyuan; Liu, Chang; Zan, Yifan; Miao, Gai; Wang, Hao; Kong, Lingzhao

2018-04-12

Porous carbon adsorbents were prepared from microalgae (Chlorococcum sp.) via directly hydrothermal carbonization coupled with KOH or NH 3 activation for Cr(VI) adsorption. KOH-activated porous carbons exhibit high Cr(VI) adsorption capacities than those obtained via NH 3 modification (370.37 > 95.70 mg/g). The superior Cr(VI) adsorption capacity is due to high surface areas (1784 m 2 /g) and pore volumes of porous carbon with mesoporous and macroporous structures. The Cr(VI) adsorption result was well fitted to the Langmuir model, showing that the removal of Cr(VI) was attributed to the monolayer adsorption of activity site on carbon surface.

Influence of porous texture and surface chemistry on the CO₂ adsorption capacity of porous carbons: acidic and basic site interactions.

PubMed

Sánchez-Sánchez, Angela; Suárez-García, Fabián; Martínez-Alonso, Amelia; Tascón, Juan M D

2014-12-10

Doped porous carbons exhibiting highly developed porosity and rich surface chemistry have been prepared and subsequently applied to clarify the influence of both factors on carbon dioxide capture. Nanocasting was selected as synthetic route, in which a polyaramide precursor (3-aminobenzoic acid) was thermally polymerized inside the porosity of an SBA-15 template in the presence of different H3PO4 concentrations. The surface chemistry and the porous texture of the carbons could be easily modulated by varying the H3PO4 concentration and carbonization temperature. Porous texture was found to be the determinant factor on carbon dioxide adsorption at 0 °C, while surface chemistry played an important role at higher adsorption temperatures. We proved that nitrogen functionalities acted as basic sites and oxygen and phosphorus groups as acidic ones toward adsorption of CO2 molecules. Among the nitrogen functional groups, pyrrolic groups exhibited the highest influence, while the positive effect of pyridinic and quaternary functionalities was smaller. Finally, some of these N-doped carbons exhibit CO2 heats of adsorption higher than 42 kJ/mol, which make them excellent candidates for CO2 capture.

Adsorption energy distribution of carbon tetrachloride on carbon nanofiber arrays prepared by template synthesis

NASA Astrophysics Data System (ADS)

Wu, Chi-Hsin; Shr, Jin-Fang; Wu, Chu-Fu; Hsieh, Chien-Te

2008-02-01

The influence of pore size distribution on adsorption energy distributions (AEDs) of aligned carbon nanofiber (CNF) arrays in vapor phase was conducted in the present study. A template-assisted synthesis was employed to fabricate aligned CNF arrays with different pore size distributions (PSDs). Adsorption isotherms of CCl 4 onto the CNF arrays were investigated within an entire pressure of 0.05-0.18 atm at 30 °C. The adsorptive surface coverage was found to decrease with the average pore size, indicating the presence of heterogeneity for gas adsorption. An AED model was postulated to describe the heterogeneous surface consisting of numerous surface pitchwises that obey a localized Langmuir model. It was found that all CNF arrays exhibit a similar Gaussian-type AED, in where the peak adsorption energy shifts to a higher energy with decreasing the pore size of CNFs. This finding can be ascribed to a fact that micropores are major providers of adsorption sites, whereas in mesopores only weaker adsorption is observed, thus resulting in the shift of energy distribution. An excellent prediction to the adsorption isotherms of CCl 4 by the AED model indicates that the PSD of CNFs acts a crucial factor in affecting the adsorptive coverage.

Determination of adsorption parameters in numerical simulation for polymer flooding

NASA Astrophysics Data System (ADS)

Bao, Pengyu; Li, Aifen; Luo, Shuai; Dang, Xu

2018-02-01

A study on the determination of adsorption parameters for polymer flooding simulation was carried out. The study mainly includes polymer static adsorption and dynamic adsorption. The law of adsorption amount changing with polymer concentration and core permeability was presented, and the one-dimensional numerical model of CMG was established under the support of a large number of experimental data. The adsorption laws of adsorption experiments were applied to the one-dimensional numerical model to compare the influence of two adsorption laws on the historical matching results. The results show that the static adsorption and dynamic adsorption abide by different rules, and differ greatly in adsorption. If the static adsorption results were directly applied to the numerical model, the difficulty of the historical matching will increase. Therefore, dynamic adsorption tests in the porous medium are necessary before the process of parameter adjustment in order to achieve the ideal history matching result.

Understanding the adsorptive and photoactivity properties of Ag-graphene oxide nanocomposites.

PubMed

Martínez-Orozco, R D; Rosu, H C; Lee, Soo-Wohn; Rodríguez-González, V

2013-12-15

Nanocomposites of graphene oxide (GO) and silver nanoparticles (AgNPs) were synthetized using a practical photochemical silver functionalization. Their photocatalytic activities were evaluated with two dyes, Rhodamine B and Indigo Carmine, under visible-light irradiation. The prepared nanocomposites were characterized by HRTEM, FESEM, XRD, Raman, FTIR and UV-vis absorption spectroscopy. These nanocomposites present new defect domains of sp(3) type in combination with several graphitic functional groups that act as nucleation sites for anchoring AgNPs, while the sp(2)-sp(3) edge defects domains of GO generate the photoactivity. Furthermore, their photocatalytic performances are governed by their large adsorption capacity, and strong interaction with dye chromophores. A comprehensive photocatalytic way underlying the importance of adsorption is suggested to explain the low visible-light responsive photoactivity of the AgNPs-GO nanocomposites and the possible binding-site saturation. Then, the usage of H2SO4 allows the production of ionic species and helps to confirm the strong adsorption of both dyes. The ability to synthesize AgNPs-GO nanocomposites with extensive adsorptive capacity is certainly of interest for the efficient removal of hazardous materials. Copyright © 2013 Elsevier B.V. All rights reserved.

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

PubMed

Goldberg, Sabine

2014-10-01

Various chemical models of ion adsorption are presented and discussed. Chemical models, such as surface complexation models, provide a molecular description of anion adsorption reactions using an equilibrium approach. Two such models, the constant capacitance model and the triple layer model, are described in the present study. Characteristics common to all the surface complexation models are equilibrium constant expressions, mass and charge balances, and surface activity coefficient electrostatic potential terms. Methods for determining parameter values for surface site density, capacitances, and surface complexation constants also are discussed. Spectroscopic experimental methods of establishing ion adsorption mechanisms include vibrational spectroscopy, nuclear magnetic resonance spectroscopy, electron spin resonance spectroscopy, X-ray absorption spectroscopy, and X-ray reflectivity. Experimental determinations of point of zero charge shifts and ionic strength dependence of adsorption results and molecular modeling calculations also can be used to deduce adsorption mechanisms. Applications of the surface complexation models to heterogeneous natural materials, such as soils, using the component additivity and the generalized composite approaches are described. Emphasis is on the generalized composite approach for predicting anion adsorption by soils. Continuing research is needed to develop consistent and realistic protocols for describing ion adsorption reactions on soil minerals and soils. The availability of standardized model parameter databases for use in chemical speciation-transport models is critical. Published 2014 Wiley Periodicals Inc. on behalf of SETAC. This article is a US Government work and as such, is in the public domain in the in the United States of America.

Retrograde adsorption isotherms: an impossible fact?

PubMed

Helfferich, Friedrich G

2005-06-24

"Retrograde" adsorption isotherms have been reported, but seem to violate thermodynamics and would cause concentration steps to migrate against the direction of fluid-phase flow. In general, what appears to be retrograde behavior is caused by one or more additional, uncontrolled variables. This is illustrated with adsorption of sulfonate on a weak-acid ion exchanger, where adsorption is accompanied by partial conversion of the ion exchanger to the sodium form.

Individual and competitive adsorption of phenol and nickel onto multiwalled carbon nanotubes

PubMed Central

Abdel-Ghani, Nour T.; El-Chaghaby, Ghadir A.; Helal, Farag S.

2014-01-01

Individual and competitive adsorption studies were carried out to investigate the removal of phenol and nickel ions by adsorption onto multiwalled carbon nanotubes (MWCNTs). The carbon nanotubes were characterized by different techniques such as X-ray diffraction, scanning electron microscopy, thermal analysis and Fourier transformation infrared spectroscopy. The different experimental conditions affecting the adsorption process were investigated. Kinetics and equilibrium models were tested for fitting the adsorption experimental data. The characterization experimental results proved that the studied adsorbent possess different surface functional groups as well as typical morphological features. The batch experiments revealed that 300 min of contact time was enough to achieve equilibrium for the adsorption of both phenol and nickel at an initial adsorbate concentration of 25 mg/l, an adsorbent dosage of 5 g/l, and a solution pH of 7. The adsorption of phenol and nickel by MWCNTs followed the pseudo-second order kinetic model and the intraparticle diffusion model was quite good in describing the adsorption mechanism. The Langmuir equilibrium model fitted well the experimental data indicating the homogeneity of the adsorbent surface sites. The maximum Langmuir adsorption capacities were found to be 32.23 and 6.09 mg/g, for phenol and Ni ions, respectively. The removal efficiency of MWCNTs for nickel ions or phenol in real wastewater samples at the optimum conditions reached up to 60% and 70%, respectively. PMID:26257938

Molecular simulation of methane adsorption characteristics on coal macromolecule

NASA Astrophysics Data System (ADS)

Yang, Zhiyuan; He, Xiaoxiao; Meng, Zhuoyue; Xue, Wenying

2018-02-01

In this paper, the molecular model of anthracite named Wender2 was selected to study the adsorption behaviour of single component CH4 and the competitive adsorption of CH4/CO2, CH4/H2O and CH4/N2. The molecular model of anthracite was established by molecular simulation software (Materials Studio 8.0), and Grand Canonical Monte Carlo (GCMC) simulations were carried out to investigate the single and binary component adsorption. The effects of pressure and temperature on the adsorption position, adsorption energy and adsorption capacity were mainly discussed. The results show that for the single component adsorption, the adsorption capacity of CH4 increases rapidly with the pressure ascending, and then tends to be stable after the first step. The low temperature is favourable for the adsorption of CH4, and the high temperature promotes desorption quantity of CH4 from the coal. Adsorbent molecules are preferentially adsorbed on the edge of coal macromolecules. The order of adsorption capacity of CH4/CO2, CH4/H2O and CH4/N2 in the binary component is H2O>CO2>CH4>N2. The change of pressure has little effect on the adsorption capacity of the adsorbent in the competitive adsorption, but it has a great influence on the adsorption capacity of the adsorbent, and there is a positive correlation between them.

Molybdenum isotope fractionation during adsorption to organic matter

USGS Publications Warehouse

King, Elizabeth K.; Perakis, Steven; Pett-Ridge, Julie C.

2018-01-01

Organic matter is of emerging interest as a control on molybdenum (Mo) biogeochemistry, and information on isotope fractionation during adsorption to organic matter can improve interpretations of Mo isotope variations in natural settings. Molybdenum isotope fractionation was investigated during adsorption onto insolubilized humic acid (IHA), a surrogate for organic matter, as a function of time (2–170 h) and pH (2–7). For the time series experiment performed at pH 4.2, the average Mo isotope fractionation between the solution and the IHA (Δ98Mosolution-IHA) was 1.39‰ (± 0.16‰, 2σ, based on 98Mo/95Mo relative to the NIST 3134 standard) at steady state. For the pH series experiment, Mo adsorption decreased as pH increased from 2.0 to 6.9, and the Δ98Mosolution-IHA increased from 0.82‰ to 1.79‰. We also evaluated natural Mo isotope patterns in precipitation, foliage, organic horizon, surface mineral soil, and bedrock from 12 forested sites in the Oregon Coast Range. The average Mo isotope offset observed between precipitation and organic (O) horizon soil was 2.1‰, with light Mo isotopes adsorbing preferentially to organic matter. Fractionation during adsorption to organic matter is similar in magnitude and direction to prior observations of Mo fractionation during adsorption to Fe- and Mn- (oxyhydr)oxides. Our finding that organic matter influences Mo isotope composition has important implications for the role of organic matter as a driver of trace metal retention and isotopic fractionation.

Molybdenum isotope fractionation during adsorption to organic matter

NASA Astrophysics Data System (ADS)

King, E. K.; Perakis, S. S.; Pett-Ridge, J. C.

2018-02-01

Organic matter is of emerging interest as a control on molybdenum (Mo) biogeochemistry, and information on isotope fractionation during adsorption to organic matter can improve interpretations of Mo isotope variations in natural settings. Molybdenum isotope fractionation was investigated during adsorption onto insolubilized humic acid (IHA), a surrogate for organic matter, as a function of time (2-170 h) and pH (2-7). For the time series experiment performed at pH 4.2, the average Mo isotope fractionation between the solution and the IHA (Δ98Mosolution-IHA) was 1.39‰ (±0.16‰, 2σ, based on 98Mo/95Mo relative to the NIST 3134 standard) at steady state. For the pH series experiment, Mo adsorption decreased as pH increased from 2.0 to 6.9, and the Δ98Mosolution-IHA increased from 0.82‰ to 1.79‰. We also evaluated natural Mo isotope patterns in precipitation, foliage, organic horizon, surface mineral soil, and bedrock from 12 forested sites in the Oregon Coast Range. The average Mo isotope offset observed between precipitation and organic (O) horizon soil was 2.1‰, with light Mo isotopes adsorbing preferentially to organic matter. Fractionation during adsorption to organic matter is similar in magnitude and direction to prior observations of Mo fractionation during adsorption to Fe- and Mn- (oxyhydr)oxides. Our finding that organic matter influences Mo isotope composition has important implications for the role of organic matter as a driver of trace metal retention and isotopic fractionation.

ADSORPTION MEDIA FOR ARSENIC REMOVAL

EPA Science Inventory

Presentation will discuss the use of adsorptive media for the removal of arsenic from drinking water. Presentation is a fundamental discussion on the use of adsorptive media for arsenic removal and includes information from several EPA field studies on removal of arsenic from dr...

Density functional study of H2O molecule adsorption on α-U(001) surface.

PubMed

Huang, Shanqisong; Zeng, Xiu-Lin; Zhao, Feng-Qi; Ju, Xuehai

2016-04-01

Periodic density functional theory (DFT) calculations were performed to investigate the adsorption of H2O on U(001) surface. The metallic nature of uranium atom and different adsorption sites of U(001) surface play key roles in the H2O molecular dissociate reaction. The long-bridge site is the most favorable site of H2O-U(001) adsorption configuration. The triangle-center site of the H atom is the most favorable site of HOH-U(001) adsorption configuration. The interaction between H2O and U surface is more evident on the first layer than that on any other two sub-layers. The dissociation energy of one hydrogen atom from H2O is -1.994 to -2.215 eV on U(001) surface, while the dissociating energy decreases to -3.351 to -3.394 eV with two hydrogen atoms dissociating from H2O. These phenomena also indicate that the Oads can promote the dehydrogenation of H2O. A significant charge transfer from the first layer of the uranium surface to the H and O atoms is also found to occur, making the bonding partly ionic.

Mechanics of adsorption-deformation coupling in porous media

NASA Astrophysics Data System (ADS)

Zhang, Yida

2018-05-01

This work extends Coussy's macroscale theory for porous materials interacting with adsorptive fluid mixtures. The solid-fluid interface is treated as an independent phase that obeys its own mass, momentum and energy balance laws. As a result, a surface strain energy term appears in the free energy balance equation of the solid phase, which further introduces the so-called adsorption stress in the constitutive equations of the porous skeleton. This establishes a fundamental link between the adsorption characteristics of the solid-fluid interface and the mechanical response of the porous media. The thermodynamic framework is quite general in that it recovers the coupled conduction laws, Gibbs isotherm and the Shuttleworth's equation for surface stress, and imposes no constraints on the magnitude of deformation and the functional form of the adsorption isotherms. A rich variety of coupling between adsorption and deformation is recovered as a result of combining different poroelastic models (isotropic vs. anisotropic, linear vs. nonlinear) and adsorption models (unary vs. mixture adsorption, uncoupled vs. stretch-dependent adsorption). These predictions are discussed against the backdrop of recent experimental data on coal swelling subjected to CO2 and CO2sbnd CH4 injections, showing the capability and versatility of the theory in capturing adsorption-induced deformation of porous materials.

Physicochemical factors affecting ethanol adsorption by activated carbon.

PubMed

Bradley, K J; Hamdy, M K; Toledo, R T

1987-03-01

Powder and granular activated charcoal were evaluated for ethanol adsorptivity from aqueous mixtures using an adsorption isotherm. Ethanol adsorption capacity was more pronounced at 25 degrees C as compared to 5, 15, and 40 degrees C. When pH of the ethanol-buffer mixture (0.09 ionic strength) was changed from acidic (2.3) to neutral and then to alkaline (11.2), ethanol adsorption was decreased. Increasing ionic strength of the ethanol-buffer mixtures from 0.05 to 0.09 enhanced ethanol adsorption but a further increase to 0.14 showed no significant effect. Ethanol adsorption was more efficient from an aqueous ethanol mixture as compared to semidefined and nondefined fermentation worts, respectively. Heating granular charcoal to 400 degrees C for 1 h and 600 degrees C for 3 h in N(2) increased ethanol adsorptivity and heating to 1000 degrees C (1 h) in CO(2) decreased it when ethanol was removed from dilute solutions by simple pass adsorption in a carbon packed column. Granular charcoal was superior to powdered charcoal and an inverse relationship was noted between the weight of the granular carbon bed in the column and ethanol adsorbed/g carbon. Decreasing the column feed flow rate from 7.5 to 2.0 L aqueous ethanol/min increased the adsorption rate.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

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

We investigated trimethylacetic acid (TMAA) adsorption on stoichiometric and oxygen-deficient CeO 2(111) surfaces using density functional theory that accounts for the on-site Coulomb interaction via a Hubbard term (DFT+U) and long-range dispersion correction. Both the molecular state and dissociative state (TMAA → TMA– + H +) were identified on stoichiometric and oxygen-deficient CeO 2(111) surfaces. For the stoichiometric surface, two thermodynamically favorable configurations with adsorption energies of the order of -30 kcal/mol are identified; one is a molecule adsorption state, and the other one is a dissociative state. For the oxygen-deficient surface, dissociative states are more favorable than molecular states.more » Moreover, the most favorable configuration is the dissociative adsorption of TMAA with the adsorption energy of the order of -77 kcal/mol. The dissociated TMA moiety takes the position of oxygen vacancy, forming three Ce–O bonds. The signature vibrational frequencies for these thermodynamically stable structures are reported as well as their electronic structures. The effects of long-range dispersion interactions are found to be negligible for geometries but important for adsorption energies.« less

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

DOE PAGES

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

2016-01-11

We investigated trimethylacetic acid (TMAA) adsorption on stoichiometric and oxygen-deficient CeO 2(111) surfaces using density functional theory that accounts for the on-site Coulomb interaction via a Hubbard term (DFT+U) and long-range dispersion correction. Both the molecular state and dissociative state (TMAA → TMA– + H +) were identified on stoichiometric and oxygen-deficient CeO 2(111) surfaces. For the stoichiometric surface, two thermodynamically favorable configurations with adsorption energies of the order of -30 kcal/mol are identified; one is a molecule adsorption state, and the other one is a dissociative state. For the oxygen-deficient surface, dissociative states are more favorable than molecular states.more » Moreover, the most favorable configuration is the dissociative adsorption of TMAA with the adsorption energy of the order of -77 kcal/mol. The dissociated TMA moiety takes the position of oxygen vacancy, forming three Ce–O bonds. The signature vibrational frequencies for these thermodynamically stable structures are reported as well as their electronic structures. The effects of long-range dispersion interactions are found to be negligible for geometries but important for adsorption energies.« less

The phosphorus fractions and adsorption-desorption characteristics in the Wuliangsuhai Lake, China.

PubMed

Wang, Xinglei; Wei, Jinxing; Bai, Na; Cha, Hancaicike; Cao, Can; Zheng, Kexuan; Liu, Ying

2018-05-11

The phosphorus (P) fractions and adsorption-desorption characteristics in the Wuliangsuhai Lake were investigated through molybdenum blue/ascorbic acid method and indoor simulation experiments, respectively. The results showed that the highest total phosphorus concentration in overlying water (W-TP) was found in S1 which was in the hypereutrophic type. The mean concentration of particulate organic phosphorus (POP) was the most abundant P fraction (31.35% of the W-TP). The results of TP contents in sediments (S-TP) indicated that the most sampling sites were in the mild level of pollution. The contents of calcium-bound P (HCl-P) and residual P (Res-P) fractions together comprised 83.03-98.10% of the S-TP. Pseudo-second-order models fitted well with the adsorption-desorption kinetic of P fractions. The Langmuir and Freundlich models well described the adsorption isotherm of P fractions. The results of adsorption-desorption of P fractions indicated that the adsorption capacity was strong, the chemical adsorption was dominant, and the sediments was a source of P. Accordingly, we concluded that the Wuliangsuhai Lake was in the moderate pollution level, and the sediments as a source could desorb P in natural aquatic environment.

The adsorption behavior of U(VI) on granite.

PubMed

Fan, Q H; Hao, L M; Wang, C L; Zheng, Z; Liu, C L; Wu, W S

2014-03-01

The effects of pH, counter ions and temperature on the adsorption of U(VI) on Beishan granite (BsG) were investigated in the presence and absence of fulvic acid (FA) and humic acid (HA). The adsorption edge of U(VI) on BsG suggested that U(VI) adsorption was mainly controlled by ion exchange and outer-sphere complexation at low pH, whereas inner-sphere complex was the dominant adsorption species in the pH range of 4.0-9.0. Above pH 9.0, Na2U2O7 might play an important role in the rise of U(VI) adsorption again. Counter ions such as Cl(-), SO4(2-) and PO4(3-) can provoke U(VI) adsorption on BsG to some extent, which was directly correlated to the complexing ability of U(VI)-ligand. More noticeably, the large enhancement of U(VI) adsorption in the presence of phosphate can be attributed to the ternary complex formation (BsG-PO4-UO2), precipitation ((UO2)3(PO4)2(s)) and secondary phase (Na-autunite). Both FA and HA can slightly increase U(VI) adsorption at low pH, whereas they strongly inhibited U(VI) adsorption at high pH range. Artificial synthesized granite (AsG) prepared in the laboratory is impossible to use as an analogue of natural granite because of the large difference in the adsorption and surface properties.

Activation thermodynamics of virus adsorption to solids.

PubMed Central

Preston, D R; Farrah, S R

1988-01-01

The kinetics of bacteriophage MS2, T2, and f2 adsorption to powdered nitrocellulose and disrupted Seitz S1 filters at pH 7 were determined as a function of temperature. Data from these studies were combined with data produced in a previous study on MS2 adsorption to clay by Stagg et al. (Appl. Environ. Microbiol. 33:385-391, 1977). These workers studied the adsorption of MS2 to bentonite clay as a function of temperature. Data from both this previous study and the current one were used to calculate the thermodynamic parameters of virus adsorption. The results show that adsorption of bacteriophages to the solids tested is a physical process (energy of activation, less than 40 kcal [168 J]/mol) rather than a chemical process (energy of activation, greater than 40 kcal/mol). The free energy of activation showed a high negative correlation (r = -0.904, r2 = 0.817) with the percentage of virus adsorption to the solids tested. The energy of activation was highly negatively correlated with the percentage of virus adsorption to nitrocellulose and clay (r = -0.913, r2 = 0.834) but poorly correlated with the percentage of virus adsorption to disrupted Seitz S1 filters (r = -0.348, r2 = 0.121). In general, under conditions in which the percentage of virus adsorption was low, the energy of activation, the free energy of activation, and the entropy of activation were high. Increasing the percentage of virus adsorbed by changing the adsorbing conditions or changing the adsorbing solid decreased the energy of activation, the free energy of activation, and the entropy of activation. PMID:3214152

Grand canonical Monte Carlo simulation of the adsorption isotherms of water molecules on model soot particles

NASA Astrophysics Data System (ADS)

Moulin, F.; Picaud, S.; Hoang, P. N. M.; Jedlovszky, P.

2007-10-01

The grand canonical Monte Carlo method is used to simulate the adsorption isotherms of water molecules on different types of model soot particles. The soot particles are modeled by graphite-type layers arranged in an onionlike structure that contains randomly distributed hydrophilic sites, such as OH and COOH groups. The calculated water adsorption isotherm at 298K exhibits different characteristic shapes depending both on the type and the location of the hydrophilic sites and also on the size of the pores inside the soot particle. The different shapes of the adsorption isotherms result from different ways of water aggregation in or/and around the soot particle. The present results show the very weak influence of the OH sites on the water adsorption process when compared to the COOH sites. The results of these simulations can help in interpreting the experimental isotherms of water adsorbed on aircraft soot.

Adsorption kinetics of SO2 on powder activated carbon

NASA Astrophysics Data System (ADS)

Li, Bing; Zhang, Qilong; Ma, Chunyuan

2018-02-01

The flue gas SO2 adsorption removal by powder activated carbon is investigated based on a fixed bed reactor. The effect of SO2 inlet concentration on SO2 adsorption is investigated and the adsorption kinetics is analyzed. The results indicated that the initial SO2 adsorption rate and the amount of SO2 adsorbed have increased with increased in SO2 inlet concentration. Gas diffusion, surface adsorption and catalytic oxidation reaction are involved in SO2 adsorption on powder activated carbon, which play a different role in different stage. The Bangham kinetics model can be used to predict the kinetics of SO2 adsorption on powder activated carbon.

High pressure adsorption isotherms of nitrogen onto granular activated carbon for a single bed pressure swing adsorption refrigeration system

NASA Astrophysics Data System (ADS)

Palodkar, Avinash V.; Anupam, Kumar; Roy, Zunipa; Saha, B. B.; Halder, G. N.

2017-10-01

Adsorption characteristics of nitrogen onto granular activated carbon for the wide range of temperature (303-323 K) and pressure (0.2027-2.0265 MPa) have been reported for a single bed pressure swing adsorption refrigeration system. The experimental data were fitted to Langmuir, Dubinin-Astakhov and Dubinin-Radushkevich (D-R) isotherms. The Langmuir and D-R isotherm models were found appropriate in correlating experimental adsorption data with an average relative error of ±2.0541% and ±0.6659% respectively. The isosteric heat of adsorption data were estimated as a function of surface coverage of nitrogen and temperature using D-R isotherm. The heat of adsorption was observed to decrease from 12.65 to 6.98 kJ.mol-1 with an increase in surface concentration at 303 K and it followed the same pattern for other temperatures. It was found that an increase in temperature enhances the magnitude of the heat of adsorption.

Adsorption properties for urokinase on local diatomite surface

NASA Astrophysics Data System (ADS)

Yang, Yuxiang; Zhang, Jianbo; Yang, Weimin; Wu, Jieda; Chen, Rongsan

2003-02-01

In this paper, adsorption isotherm of urokinase on two typical local diatomites were determined at 25 °C and their surface electrical potentials (ζ), isoelectrical point values (IEP) were determined. The properties of diatomites, the relationship among diatomite structure, pore-size distribution, surface ζ and adsorption isotherm were discussed. The adsorption equation of urokinase was calculated from the adsorption isotherm. The adsorption mode of urokinase on diatomite surface was judged by the configuration function α. The relationship between the amount of adsorbed urokinase and IEP value was also discussed.

Charge induced enhancement of adsorption for hydrogen storage materials

NASA Astrophysics Data System (ADS)

Sun, Xiang

2009-12-01

. Direct measurement of the amount of hydrogen adsorption was also carried out with porous nickel oxides and magnesium oxides using the piezoelectric material PMN-PT as the charge supplier due to the pressure. The adsorption enhancement from the PMN-PT generated charges is obvious at hydrogen pressure between 0 and 60 bars, where the hydrogen uptake is increased at about 35% for nickel oxide and 25% for magnesium oxide. Computer simulation reveals that under the external electric field, the electron cloud of hydrogen molecules is pulled over to the adsorbent site and can overlap with the adsorbent electrons, which in turn enhances the adsorption energy. Experiments were also carried out to examine the effects of hydrogen spillover with charge induced enhancement. The results show that the overall storage capacity in nickel oxide increased remarkably by a factor of 4.

On the Structure-Property Relationships of Cation-Exchanged ZK-5 Zeolites for CO 2 Adsorption

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pham, Trong D.; Hudson, Matthew R.; Brown, Craig M.

2017-02-16

The CO 2 adsorption properties of cation-exchanged Li-, Na-, K-, and Mg-ZK-5 zeolites were correlated to the molecular structures determined by Rietveld refinements of synchrotron powder X-ray diffraction patterns. Li-, K-, and Na-ZK-5 all exhibited high isosteric heats of adsorption (Qst) at low CO 2 coverage, with Na-ZK-5 having the highest Qst (ca. 49 kJ mol -1). Mg2+ was located at the center of the zeolite hexagonal prism with the cation inaccessible to CO 2, leading to a much lower Qst (ca. 30 kJ mol-1) and lower overall uptake capacity. Multiple CO 2 adsorption sites were identified at a givenmore » CO 2 loading amount for all four cation-exchanged ZK-5 adsorbents. Site A at the flat eight-membered ring windows and site B/B* in the γ-cages were the primary adsorption sites in Li - and Na-ZK-5 zeolites. Relatively strong dual-cation adsorption sites contributed significantly to an enhanced electrostatic interaction for CO 2 in all ZK-5 samples. This interaction gives rise to a migration of Li + and Mg 2+ cations from their original locations at the center of the hexagonal prisms toward the α-cages, in which they interact more strongly with the adsorbed CO 2.« less

Effective adsorption of malachite green using magnetic barium phosphate composite from aqueous solution.

PubMed

Zhang, Fan; Wei, Zhong; Zhang, Wanning; Cui, Haiyan

2017-07-05

Magnetic Ba 3 (PO 4 ) 2 /Fe 3 O 4 -nanoparticle (called BPFN) was prepared, characterized, and developed as a low-cost adsorbent for malachite green (MG) from aqueous solution. Factors such as adsorption temperature, pH of solution, dosage of adsorbent, adsorption kinetics and isotherms were investigated. The maximum adsorption capacity obtained in this work was 1639mgg -1 at 45°C and pH6. The adsorption process fitted the pseudo-first-order kinetic model and Langmuir isotherm model. Evidences from zeta potential, Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS) data revealed that the adsorption process was driven by electrostatic attraction, the interaction between Lewis base N(CH 3 ) 2 in MG and Lewis acid Ba sites of BPFN. In addition, the BPFN could be easily regenerated by a magnet and the adsorption capacity maintained at 70% after five cycles. The present study suggests that the BPFN had high potential of removing MG from wastewater. Copyright © 2017 Elsevier B.V. All rights reserved.

Macroscopic and spectroscopic investigations of the adsorption of nitroaromatic compounds on graphene oxide, reduced graphene oxide, and graphene nanosheets.

PubMed

Chen, Xiaoxiao; Chen, Baoliang

2015-05-19

The surface properties and adsorption mechanisms of graphene materials are important for potential environmental applications. The adsorption of m-dinitrobenzene, nitrobenzene, and p-nitrotoluene onto graphene oxide (GO), reduced graphene oxide (RGO), and graphene (G) nanosheets was investigated using IR spectroscopy to probe the molecular interactions of graphene materials with nitroaromatic compounds (NACs). The hydrophilic GO displayed the weakest adsorption capability. The adsorption of RGO and G was significantly increased due to the recovery of hydrophobic π-conjugation carbon atoms as active sites. RGO nanosheets, which had more defect sites than did GO or G nanosheets, resulted in the highest adsorption of NACs which was 10-50 times greater than the reported adsorption of carbon nanotubes. Superior adsorption was dominated by various interaction modes including π-π electron donor-acceptor interactions between the π-electron-deficient phenyls of the NACs and the π-electron-rich matrix of the graphene nanosheets, and the charge electrostatic and polar interactions between the defect sites of graphene nanosheets and the -NO2 of the NAC. The charge transfer was initially proved by FTIR that a blue shift of asymmetric -NO2 stretching was observed with a concomitant red shift of symmetric -NO2 stretching after m-dinitrobenzene was adsorbed. The multiple interaction mechanisms of the adsorption of NAC molecule onto flat graphene nanosheets favor the adsorption, detection, and transformation of explosives.

Designing transition metal surfaces for their adsorption properties and chemical reactivity

NASA Astrophysics Data System (ADS)

Montemore, Matthew M.

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

Adsorption interactions of humic acids with biocides

NASA Astrophysics Data System (ADS)

Mal'Tseva, E. V.; Ivanov, A. A.; Yudina, N. V.

2009-11-01

The chemical composition of humic acids from brown coal (Aldrich) was determined by element analysis, 13C NMR spectroscopy, and potentiometric titration. The adsorption ability of humic acids with different biocides (cyproconasol, propiconasol, tebuconasol, irgarol 1051, and DCOIT) was studied. The adsorption ability of a mixture of biocides in aqueous solutions was higher than that of the individual components. The limiting concentration of humic acids at which adsorption of biocides was maximum was determined. Adsorption constants were calculated by the Freundlich equation for each biocide in aqueous solution.

Fibrinogen adsorption on blocked surface of albumin.

PubMed

Holmberg, Maria; Hou, Xiaolin

2011-05-01

We have investigated the adsorption of albumin and fibrinogen onto PET (polyethylene terephthalate) and glass surfaces and how pre-adsorption of albumin onto these surfaces can affect the adsorption of later added fibrinogen. For materials and devices being exposed to blood, adsorption of fibrinogen is often a non-wanted event, since fibrinogen is part of the clotting cascade and unspecific adsorption of fibrinogen can have an influence on the activation of platelets. Albumin is often used as blocking agent for avoiding unspecific protein adsorption onto surfaces in devices designed to handle biological samples, including protein solutions. It is based on the assumption that proteins adsorbs as a monolayer on surfaces and that proteins do not adsorb on top of each other. By labelling albumin and fibrinogen with two different radioactive iodine isotopes that emit gamma radiation with different energies, the adsorption of both albumin and fibrinogen has been monitored simultaneously on the same sample. Information about topography and coverage of adsorbed protein layers has been obtained using AFM (Atomic Force Microscopy) analysis in liquid. Our studies show that albumin adsorbs in a multilayer fashion on PET and that fibrinogen adsorbs on top of albumin when albumin is pre-adsorbed on the surfaces. Copyright © 2010 Elsevier B.V. All rights reserved.

The Accelerated Late Adsorption of Pulmonary Surfactant

PubMed Central

2011-01-01

Adsorption of pulmonary surfactant to an air−water interface lowers surface tension (γ) at rates that initially decrease progressively, but which then accelerate close to the equilibrium γ. The studies here tested a series of hypotheses concerning mechanisms that might cause the late accelerated drop in γ. Experiments used captive bubbles and a Wilhelmy plate to measure γ during adsorption of vesicles containing constituents from extracted calf surfactant. The faster fall in γ reflects faster adsorption rather than any feature of the equation of state that relates γ to surface concentration (Γ). Adsorption accelerates when γ reaches a critical value rather than after an interval required to reach that γ. The hydrophobic surfactant proteins (SPs) represent key constituents, both for reaching the γ at which the acceleration occurs and for producing the acceleration itself. The γ at which rates of adsorption increase, however, is unaffected by the Γ of protein in the films. In the absence of the proteins, a phosphatidylethanolamine, which, like the SPs, induces fusion of the vesicles with the interfacial film, also causes adsorption to accelerate. Our results suggest that the late acceleration is characteristic of adsorption by fusion of vesicles with the nascent film, which proceeds more favorably when the Γ of the lipids exceeds a critical value. PMID:21417351

Trends in adsorption of electrocatalytic water splitting intermediates on cubic ABO 3 oxides

DOE PAGES

Montoya, Joseph H.; Doyle, Andrew D.; Nørskov, Jens K.; ...

2018-01-19

The reactivity of solid oxide surfaces towards adsorption of oxygen and hydrogen is a key metric for the design of new catalysts for electrochemical water splitting. Here, in this paper, we report on trends in the adsorption energy of different adsorbed intermediates derived from the oxidation and reduction of water for ternary ABO 3 oxides in the cubic perovskite structure. Our findings support a previously reported trend that rationalizes the observed lower bound in oxygen evolution (OER) overpotentials from correlations in OH* and OOH* adsorption energies. In addition, we report hydrogen adsorption energies that may be used to estimate hydrogenmore » evolution (HER) overpotentials along with potential metrics for electrochemical metastability in reducing environments. Finally, we also report and discuss trends between atom-projected density of states and adsorption energies, which may enable a design criteria from the local electronic structure of the active site.« less

Trends in adsorption of electrocatalytic water splitting intermediates on cubic ABO 3 oxides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Montoya, Joseph H.; Doyle, Andrew D.; Nørskov, Jens K.

The reactivity of solid oxide surfaces towards adsorption of oxygen and hydrogen is a key metric for the design of new catalysts for electrochemical water splitting. Here, in this paper, we report on trends in the adsorption energy of different adsorbed intermediates derived from the oxidation and reduction of water for ternary ABO 3 oxides in the cubic perovskite structure. Our findings support a previously reported trend that rationalizes the observed lower bound in oxygen evolution (OER) overpotentials from correlations in OH* and OOH* adsorption energies. In addition, we report hydrogen adsorption energies that may be used to estimate hydrogenmore » evolution (HER) overpotentials along with potential metrics for electrochemical metastability in reducing environments. Finally, we also report and discuss trends between atom-projected density of states and adsorption energies, which may enable a design criteria from the local electronic structure of the active site.« less

[Adsorption of perfluorooctanesulfonate (PFOS) onto modified activated carbons].

PubMed

Tong, Xi-Zhen; Shi, Bao-You; Xie, Yue; Wang, Dong-Sheng

2012-09-01

Modified coal and coconut shell based powdered activated carbons (PACs) were prepared by FeCl3 and medium power microwave treatment, respectively. Batch experiments were carried out to evaluate the characteristics of adsorption equilibrium and kinetics of perfluorooctanesulfonate (PFOS) onto original and modified PACs. Based on pore structure and surface functional groups characterization, the adsorption behaviors of modified and original PACs were compared. The competitive adsorption of humic acid (HA) and PFOS on original and modified coconut shell PACs were also investigated. Results showed that both Fe3+ and medium power microwave treatments changed the pore structure and surface functional groups of coal and coconut shell PACs, but the changing effects were different. The adsorption of PFOS on two modified coconut shell-based PACs was significantly improved. While the adsorption of modified coal-based activated carbons declined. The adsorption kinetics of PFOS onto original and modified coconut shell-based activated carbons were the same, and the time of reaching adsorption equilibrium was about 6 hours. In the presence of HA, the adsorption of PFOS by modified PAC was reduced but still higher than that of the original.

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

NASA Astrophysics Data System (ADS)

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

2015-04-01

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

Adsorption of aliphatic polyhydroxy carboxylic acids on gibbsite: pH dependency and importance of adsorbate structure.

PubMed

Schneckenburger, Tatjana; Riefstahl, Jens; Fischer, Klaus

2018-01-01

Aliphatic (poly)hydroxy carboxylic acids [(P)HCA] occur in natural, e.g. soils, and in technical (waste disposal sites, nuclear waste repositories) compartments . Their distribution, mobility and chemical reactivity, e.g. complex formation with metal ions and radionuclides, depend, among others, on their adsorption onto mineral surfaces. Aluminium hydroxides, e.g. gibbsite [α-Al(OH) 3 ], are common constituents of related solid materials and mimic the molecular surface properties of clay minerals. Thus, the study was pursued to characterize the adsorption of glycolic, threonic, tartaric, gluconic, and glucaric acids onto gibbsite over a wide pH and (P)HCA concentration range. To consider specific conditions occurring in radioactive wastes, adsorption applying an artificial cement pore water (pH 13.3) as solution phase was investigated additionally. The sorption of gluconic acid at pH 4, 7, 9, and 12 was best described by the "two-site" Langmuir isotherm, combining "high affinity" sorption sites (adsorption affinity constants [Formula: see text] > 1 L mmol -1 , adsorption capacities < 6.5 mmol kg -1 ) with "low affinity" sites ([Formula: see text] < 0.1 L mmol -1 , adsorption capacities ≥ 19 mmol kg -1 ). The total adsorption capacities at pH 9 and 12 were roughly tenfold of that at pH 4 and 7. The S-shaped pH sorption edge of gluconic acid was modelled applying a constant capacitance model, considering electrostatic interactions, hydrogen bonding, surface complex formation, and formation of solved polynuclear complexes between Al 3+ ions and gluconic acid. A Pearson and Spearman rank correlation between (P)HCA molecular properties and adsorption parameters revealed the high importance of the size and the charge of the adsorbates. The adsorption behaviour of (P)HCAs is best described by a combination of adsorption properties of carboxylic acids at acidic pH and of polyols at alkaline pH. Depending on the molecular properties of the adsorbates and

ADSORPTION MECHANISMS AND TRANSPORT BEHAVIOR BETWEEN SELENATE AND SELENITE ON DIFFERENT SORBENTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Snyder, Michelle MV; Um, Wooyong

Adsorption of different oxidation species of selenium (Se), selenate (SeO42-) and selenite (SeO32-), with varying pHs (2 - 10) and ionic strengths (I = 0.01 M, 0.1 M and 1.0 M NaNO3) was measured on quartz, aluminum oxide, and synthetic iron oxide (ferrihydrite) using batch reactors to obtain a more detailed understanding of the adsorption mechanisms (e.g., inner- and outer-sphere complex). In addition to the batch experiments with single minerals contained in native Hanford Site sediment, additional batch adsorption studies were conducted with native Hanford Site sediment and groundwater as a function of 1) total Se concentration (from 0.01 tomore » 10 mg L-1) and 2) soil to solution ratios (1:20 and 1:2 grams per mL). Results from these batch studies were compared to a set of saturated column experiments that were conducted with natural Hanford sediment and groundwater spiked with either selenite or selenate to observe the transport behavior of these species. Both batch and column results indicated that selenite adsorption was consistently higher than that of selenate in all experimental conditions used. These different adsorption mechanisms between selenite and selenate result in the varying mobility of Se in the subsurface environment and explain the dependence on the oxidation species.« less

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

DOE PAGES

Li, Meijun; Tumuluri, Uma; Wu, Zili; ...

2015-09-25

Here, high-surface-area nanosized CeO 2 and M-doped CeO 2 (M=Cu, La, Zr, and Mg) prepared by a surfactant-templated method were tested for CO 2 adsorption. Cu, La, and Zr are doped into the lattice of CeO 2, whereas Mg is dispersed on the CeO 2 surface. The doping of Cu and La into CeO 2 leads to an increase of the CO 2 adsorption capacity, whereas the doping of Zr has little or no effect. The addition of Mg causes a decrease of the CO 2 adsorption capacity at a low Mg content and a gradual increase at a highermore » content. The CO 2 adsorption capacity follows the sequence Cu-CeO 2>La-CeO 2>Zr-CeO 2≈CeO 2>Mg-CeO 2 at low dopant contents, in line with the relative amount of defect sites in the samples. It is the defect sites on the surface, not in the bulk of CeO 2, modified by the dopants that play the vital role in CO 2 chemisorption. Lastly, the role of surface oxygen vacancies is further supported by an in situ IR spectroscopic study of the surface chemistry during CO 2 adsorption on the doped CeO 2.« less

Selective adsorption of thiophenic compounds from fuel over TiO2/SiO2 under UV-irradiation.

PubMed

Miao, Guang; Ye, Feiyan; Wu, Luoming; Ren, Xiaoling; Xiao, Jing; Li, Zhong; Wang, Haihui

2015-12-30

This study investigates selective adsorption of thiophenic compounds from fuel over TiO2/SiO2 under UV-irradiation. The TiO2/SiO2 adsorbents were prepared and then characterized by N2 adsorption, X-ray diffraction and X-ray photoelectron spectroscopy. Adsorption isotherms, selectivity and kinetics of TiO2/SiO2 were measured in a UV built-in batch reactor. It was concluded that (a) with the employment of UV-irradiation, high organosulfur uptake of 5.12 mg/g was achieved on the optimized 0.3TiO2/0.7SiO2 adsorbent at low sulfur concentration of 15 ppmw-S, and its adsorption selectivity over naphthalene was up to 325.5; (b) highly dispersed TiO2 served as the photocatalytic sites for DBT oxidation, while SiO2 acted as the selective adsorption sites for the corresponding oxidized DBT using TiO2 as a promoter, the two types of active sites worked cooperatively to achieve the high adsorption selectivity of TiO2/SiO2; (c) The kinetic rate-determining step for the UV photocatalysis-assisted adsorptive desulfurization (PADS) over TiO2/SiO2 was DBT oxidation; (d) consecutive adsorption-regeneration cycles suggested that the 0.3TiO2/0.7SiO2 adsorbent can be regenerated by acetonitrile washing followed with oxidative air treatment. This work demonstrated an effective PADS approach to greatly enhance adsorption capacity and selectivity of thiophenic compounds at low concentrations for deep desulfurization under ambient conditions. Copyright © 2015 Elsevier B.V. All rights reserved.

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

PubMed

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

2015-10-07

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.

Adsorption of MCPA on goethite and humic acid-coated goethite.

PubMed

Iglesias, A; López, R; Gondar, D; Antelo, J; Fiol, S; Arce, F

2010-03-01

Anionic pesticides are adsorbed on the mineral oxide fraction of the soil surface but considerably less on the organic fraction, so that the presence of organic matter causes a decrease in the amount of pesticide adsorbed, and may affect the mechanism of adsorption. In the present study we investigated the adsorption of the weak acid pesticide MCPA on the surface of goethite and of humic acid-coated goethite, selected as models of the mineral oxide fraction and organic components present in soil systems. Adsorption of the anionic form of the pesticide on goethite fitted an S-type isotherm and the amount adsorbed increased as the ionic strength decreased and the pH of the medium decreased. Application of the charge distribution multi site complexation model (CD-MUSIC model) enabled interpretation of the results, which suggested the formation of inner and outer sphere complexes between the pesticide and the singly-coordinated surface sites of goethite. Less pesticide was adsorbed on the humic acid-coated goethite than on the bare goethite and the pattern fitted an L-type isotherm, which indicates a change in the mechanism of adsorption. Simplified calculations with the CD-MUSIC model enabled interpretation of the results, which suggested that the pesticide molecules form the same type of surface complexes as in the previous case. Copyright (c) 2009 Elsevier Ltd. All rights reserved.

Adsorption of anionic and nonionic surfactant mixtures from synthetic detergents on soils.

PubMed

Rao, Pinhua; He, Ming

2006-05-01

Adsorption of anionic surfactant (sodium dodecylbenzenesulfonate, SDBS) and nonionic surfactant (an alcohol ethoxylates with 12 carbons and 9 oxyethyl groups, A12E9) mixtures, widely used as the major constituents of synthetic detergents in China and become the most common pollutants in the environment, on soils was conducted to investigate the behavior of mixed surfactants in soils. The effects of addition order and mixing ratios of two surfactants, associated with pH and ion strength in solutions, on adsorptions were considered. The results show that saturated adsorption amount of SDBS and A12E9 on soils decreased respectively when A12E9 was added into soils firstly compared with that secondly, possibly resulting from the screening of A12E9 to part adsorption sites on soils and the hydrocarbon chain-chain interactions between SDBS and A12E9. The adsorption of SDBS and A12E9 on soils was enhanced each other at pre-plateau region of isotherms. At plateau region of isotherms, the adsorption of SDBS on soils decreased with the increase of molar fraction of A12E9 in mixed surfactant solutions, while that of A12E9 increased except the molar ratio of SDBS to A12E9 0.0:1.0. With the increase of pH in mixed surfactant solutions, adsorption amount of SDBS and A12E9 on soils decreased, respectively. The reduction of ion strength in soils resulted in the decrease of adsorption amount of SDBS and A12E9 on soils, respectively.

Comparison of the Adsorption of Original and Biosimilar Preparations of Filgrastim on Infusion Sets and the Inhibition of Adsorption by Polysorbate 80.

PubMed

Tange, Mio; Matsumoto, Akino; Yoshida, Miyako; Kojima, Honami; Haraguchi, Tamami; Uchida, Takahiro

2017-01-01

The purpose of the study was to evaluate the adsorption of filgrastim on infusion sets (comprising infusion bag, line and filter) and to compare the adsorption of the original filgrastim preparation with biosimilar preparations using HPLC. The inhibitory effect of polysorbate 80 on this adsorption was also evaluated. Filgrastim was mixed with isotonic sodium chloride solution or 5% (w/v) glucose solution in the infusion fluid. Filgrastim adsorption on infusion sets was observed with all preparations and with both types of infusion solution. The adsorption ratio was about 30% in all circumstances. Filgrastim adsorption on all parts of the infusion set (bag, line and filter) was dramatically decreased by the addition of polysorbate 80 solution at concentrations at or over its critical micelle concentration (CMC). The filgrastim adsorption ratio was highest at a solution pH of 5.65, which is the isoelectric point (pI) of filgrastim. This study showed that the degree of filgrastim adsorption on infusion sets is similar for original and biosimilar preparations, but that the addition of polysorbate 80 to the infusion solution at concentrations at or above its CMC is effective in preventing filgrastim adsorption. The addition of a total-vitamin preparation with a polysorbate 80 concentration over its CMC may be an effective way of preventing filgrastim adsorption on infusion sets.

Competitive Adsorption of Metals onto Magnetic Graphene Oxide: Comparison with Other Carbonaceous Adsorbents

PubMed Central

Hur, Jin; Shin, Jaewon; Yoo, Jeseung; Seo, Young-Soo

2015-01-01

Competitive adsorption isotherms of Cu(II), Pb(II), and Cd(II) were examined on a magnetic graphene oxide (GO), multiwalled carbon nanotubes (MWCNTs), and powered activated carbon (PAC). A series of analyses confirmed the successful synthesis of the magnetic GO based on a simple ultrasonification method. Irrespective of the adsorbents, the adsorption was highly dependent on pH, and the adsorption was well described by the Langmuir isotherm model. The maximum adsorption capacities of the adsorbents were generally higher in the order of Pb(II) > Cu(II) > Cd(II), which is the same as the degree of the electronegativity and the hydrated radius of the metals, suggesting that the metal adsorption may be governed by an ion exchange between positively charged metals and negatively charged surfaces, as well as diffusion of metals into the surface layer. The adsorption of each metal was mostly lower for multi- versus single-metal systems. The antagonistic effects were influenced by solution pH as well as the type of metals, and they were higher in the order of the magnetic GO > MWCNT > PAC. Dissolved HS played a greater role than HS adsorbed onto the adsorbents, competing with the adsorption sites for metal complexation. PMID:25861683

Molecular dynamics simulations of cesium adsorption on illite nanoparticles.

PubMed

Lammers, Laura N; Bourg, Ian C; Okumura, Masahiko; Kolluri, Kedarnath; Sposito, Garrison; Machida, Masahiko

2017-03-15

The charged surfaces of micaceous minerals, especially illite, regulate the mobility of the major radioisotopes of Cs ( 134 Cs, 135 Cs, 137 Cs) in the geosphere. Despite the long history of Cs adsorption studies, the nature of the illite surface sites remains incompletely understood. To address this problem, we present atomistic simulations of Cs competition with Na for three candidate illite adsorption sites - edge, basal plane, and interlayer. Our simulation results are broadly consistent with affinities and selectivities that have been inferred from surface complexation models. Cation exchange on the basal planes is thermodynamically ideal, but exchange on edge surfaces and within interlayers shows complex, thermodynamically non-ideal behavior. The basal planes are weakly Cs-selective, while edges and interlayers have much higher affinity for Cs. The dynamics of NaCs exchange are rapid for both cations on the basal planes, but considerably slower for Cs localized on edge surfaces. In addition to new insights into Cs adsorption and exchange with Na on illite, we report the development of a methodology capable of simulating fully-flexible clay mineral nanoparticles with stable edge surfaces using a well-tested interatomic potential model. Copyright © 2016 Elsevier Inc. All rights reserved.

Thermodynamics of Methane Adsorption on Copper HKUST-1 at Low Pressure.

PubMed

Wu, Di; Guo, Xiaofeng; Sun, Hui; Navrotsky, Alexandra

2015-07-02

Metal-organic frameworks (MOFs) can be engineered as natural gas storage materials by tuning the pore structures and surface properties. Here we report the direct measurement of CH4 adsorption enthalpy on a paddlewheel MOF (Cu HKUST-1) using gas adsorption calorimetry at 25 °C at low pressures (below 1 bar). In this pressure region, the CH4-CH4 intermolecular interactions are minimized and the energetics solely reflects the CH4-MOF interactions. Our results suggest moderately exothermic physisorption with an enthalpy of -21.1 ± 1.1 kJ/mol CH4 independent of coverage. This calorimetric investigation complements previous computational and crystallographic studies by providing zero coverage enthalpies of CH4 adsorption. The analysis of the new and literature data suggests that in initial stages of adsorption the CH4-HKUST-1 interaction tends to be more sensitive to the pore dimension than to the guest polarizability, suggesting a less specific chemical binding role for the open Cu site.

Thermodynamics of methane adsorption on copper HKUST-1 at low pressure

DOE PAGES

Wu, Di; Guo, Xiaofeng; Sun, Hui; ...

2015-06-11

Metal–organic frameworks (MOFs) can be engineered as natural gas storage materials by tuning the pore structures and surface properties. Here we report the direct measurement of CH₄ adsorption enthalpy on a paddlewheel MOF (Cu HKUST-1) using gas adsorption calorimetry at 25 °C at low pressures (below 1 bar). In this pressure region, the CH₄–CH₄ intermolecular interactions are minimized and the energetics solely reflects the CH₄–MOF interactions. Our results suggest moderately exothermic physisorption with an enthalpy of -21.1 ± 1.1 kJ/mol CH₄ independent of coverage. The calorimetric investigation complements previous computational and crystallographic studies by providing zero coverage enthalpies of CH₄more » adsorption. The analysis of the new and literature data suggests that in initial stages of adsorption the CH₄–HKUST-1 interaction tends to be more sensitive to the pore dimension than to the guest polarizability, suggesting a less specific chemical binding role for the open Cu site.« less

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

PubMed

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

2016-02-01

Excessive phosphate in wastewater should be removed to control eutrophication of water bodies. The potential of employing amorphous zirconium (Zr) hydroxide to remove phosphate from synthetic wastewater was studied in batch adsorption experiments and in a submerged membrane filtration adsorption hybrid (MFAH) reactor. The adsorption data satisfactorily fitted to Langmuir, pseudo-first order and pseudo-second order models. Langmuir adsorption maxima at 22 °C and pHs of 4.0, 7.1, and 10.0 were 30.40, 18.50, and 19.60 mg P/g, respectively. At pH 7.1 and temperatures of 40 °C and 60 °C, they were 43.80 and 54.60 mg P/g, respectively. The thermodynamic parameters, ΔG° and ΔS° were negative and ΔH° was positive. FTIR, zeta potential and competitive phosphate, sulphate and nitrate adsorption data showed that the mechanism of phosphate adsorption was inner-sphere complexation. In the submerged MFAH reactor experiment, when Zr hydroxide was added at doses of 1-5 g/L once only at the start of the experiment, the removal of phosphate from 3 L of wastewater containing 10 mg P/L declined after 5 h of operation. However, when Zr hydroxide was repeatedly added at 5 g/L dose every 24 h, satisfactory removal of phosphate was maintained for 3 days. Copyright © 2015 Elsevier Ltd. All rights reserved.

Competitive adsorption-desorption reactions of two hazardous heavy metals in contaminated soils.

PubMed

Davari, Masoud; Rahnemaie, Rasoul; Homaee, Mehdi

2015-09-01

Investigating the interactions of heavy metals is imperative for sustaining environment and human health. Among those, Cd is toxic for organisms at any concentration. While Ni acts as a micronutrient at very low concentration but is hazardous toxic above certain threshold value. In this study, the chemical adsorption and desorption reactions of Ni and Cd in contaminated soils were investigated in both single and binary ion systems. Both Ni and Cd experimental data demonstrated Langmuir type adsorption. In the competitive systems, an antagonistic effect was observed, implying that both ions compete for same type of adsorption sites. Adverse effect of Cd on Ni adsorption was slightly stronger than that of opposite system, consistent with adsorption isotherms in single ion systems. Variation in ionic strength indicated that Ca, a much weaker adsorbate, could also compete with Cd and Ni for adsorption on soil particles. Desorption data indicated that Cd and Ni are adsorbed very tightly such that after four successive desorption steps, less than 0.5 % of initially adsorbed ions released into the soil solution. This implies that Ca, at concentration in equilibrium with calcite mineral, cannot adequately compete with and replace adsorbed Ni and Cd ions. This adsorption behavior was led to considerable hysteresis between adsorption and desorption in both single and binary ion systems. In the binary ion systems, desorption of Cd and Ni was increased by increase in both equilibrium concentration of adsorbed ion and concentration of competitor ion. The overall results obtained in this research indicate that Cd and Ni are strongly adsorbed in calcareous soil and Ca, the major dissolved ion, insignificantly influences metal ions adsorption. Consequently, the contaminated soils by Ni and Cd can simultaneously be remediated by environmentally oriented technologies such as phytoremediation.

Efficiently mapping structure-property relationships of gas adsorption in porous materials: application to Xe adsorption.

PubMed

Kaija, A R; Wilmer, C E

2017-09-08

Designing better porous materials for gas storage or separations applications frequently leverages known structure-property relationships. Reliable structure-property relationships, however, only reveal themselves when adsorption data on many porous materials are aggregated and compared. Gathering enough data experimentally is prohibitively time consuming, and even approaches based on large-scale computer simulations face challenges. Brute force computational screening approaches that do not efficiently sample the space of porous materials may be ineffective when the number of possible materials is too large. Here we describe a general and efficient computational method for mapping structure-property spaces of porous materials that can be useful for adsorption related applications. We describe an algorithm that generates random porous "pseudomaterials", for which we calculate structural characteristics (e.g., surface area, pore size and void fraction) and also gas adsorption properties via molecular simulations. Here we chose to focus on void fraction and Xe adsorption at 1 bar, 5 bar, and 10 bar. The algorithm then identifies pseudomaterials with rare combinations of void fraction and Xe adsorption and mutates them to generate new pseudomaterials, thereby selectively adding data only to those parts of the structure-property map that are the least explored. Use of this method can help guide the design of new porous materials for gas storage and separations applications in the future.

Phase 2 Methyl Iodide Deep-Bed Adsorption Tests

DOE Office of Scientific and Technical Information (OSTI.GOV)

Soelberg, Nick; Watson, Tony

2014-09-01

Nuclear fission produces fission products (FPs) and activation products, including iodine-129, which could evolve into used fuel reprocessing facility off-gas systems, and could require off-gas control to limit air emissions to levels within acceptable emission limits. Research, demonstrations, and some reprocessing plant experience have indicated that diatomic iodine can be captured with efficiencies high enough to meet regulatory requirements. Research on the capture of organic iodides has also been performed, but to a lesser extent. Several questions remain open regarding the capture of iodine bound in organic compounds. Deep-bed methyl iodide adsorption testing has progressed according to a multi-laboratory methylmore » iodide adsorption test plan. This report summarizes the second phase of methyl iodide adsorption work performed according to this test plan using the deep-bed iodine adsorption test system at the Idaho National Laboratory (INL), performed during the second half of Fiscal Year (FY) 2014. Test results continue to show that methyl iodide adsorption using AgZ can achieve total iodine decontamination factors (DFs, ratios of uncontrolled and controlled total iodine levels) above 1,000, until breakthrough occurred. However, mass transfer zone depths are deeper for methyl iodide adsorption compared to diatomic iodine (I2) adsorption. Methyl iodide DFs for the Ag Aerogel test adsorption efficiencies were less than 1,000, and the methyl iodide mass transfer zone depth exceeded 8 inches. Additional deep-bed testing and analyses are recommended to (a) expand the data base for methyl iodide adsorption under various conditions specified in the methyl iodide test plan, and (b) provide more data for evaluating organic iodide reactions and reaction byproducts for different potential adsorption conditions.« less

Functionalized SBA-15 materials for bilirubin adsorption

NASA Astrophysics Data System (ADS)

Tang, Tao; Zhao, Yanling; Xu, Yao; Wu, Dong; Xu, Jun; Deng, Feng

2011-05-01

To investigate the driving force for bilirubin adsorption on mesoporous materials, a comparative study was carried out between pure siliceous SBA-15 and three functionalized SBA-15 mesoporous materials: CH 3-SBA-15 (MS), NH 2-SBA-15 (AS), and CH 3/NH 2-SBA-15 (AMS) that were synthesized by one-pot method. The obtained materials exhibited large surface areas (553-810 m 2/g) and pore size (6.6-7.1 nm) demonstrated by XRD and N 2-ad/desorption analysis. The SEM images showed that the materials had similar fiberlike morphology. The functionalization extent was calculated according to 29Si MAS NMR spectra and it was close to the designed value (10%). The synthesized mesoporous materials were used as bilirubin adsorbents and showed higher bilirubin adsorption capacities than the commercial active carbon. The adsorption capacities of amine functionalized samples AMS and AS were larger than those of pure siliceous SBA-15 and MS, indicating that electrostatic interaction was the dominant driving force for bilirubin adsorption on mesoporous materials. Increasing the ionic strength of bilirubin solution by adding NaCl would decrease the bilirubin adsorption capacity of mesoporous material, which further demonstrated that the electrostatic interaction was the dominant driving force for bilirubin adsorption. In addition, the hydrophobic interaction provided by methyl groups could promote the bilirubin adsorption.

Evaluation of ferrolysis in arsenate adsorption on the paddy soil derived from an Oxisol.

PubMed

Jiang, Jun; Dai, Zhaoxia; Sun, Rui; Zhao, Zhenjie; Dong, Ying; Hong, Zhineng; Xu, Renkou

2017-07-01

Iron oxides are dominant effective adsorbents for arsenate in iron oxide-rich variable charge soils. Oxisol-derived paddy soils undergo intensive ferrolysis, which results in high leaching and transformation of iron oxides. However, little information is available concerning the effect of ferrolysis on arsenate adsorption by paddy soil and parent Oxisol. In the present study, we examined the arsenate affinity of soils using arsenate adsorption/desorption isotherms, zeta potential, adsorption kinetics, pH effect and phosphate competition experiments. Results showed that ferrolysis in an alternating flooding-drying Oxisol-derived paddy soil resulted in a significant decrease of free iron oxides and increase of amorphous iron oxides in the surface and subsurface layers. There were more reactive sites exposed on amorphous than on crystalline iron oxides. Therefore, disproportionate ratios of arsenate adsorption capacities and contents of free iron oxides were observed in the studied Oxisols compared with paddy soils. The Gibbs free energy values corroborated that both electrostatic and non-electrostatic adsorption mechanisms contributed to the arsenate adsorption by bulk soils, and the kinetic adsorption data further suggested that the rate-limiting step was chemisorption. The zeta potential of soil colloids decreased after arsenate was adsorbed on the surfaces, forming inner-sphere complexes and thus transferring their negative charges to the soil particle surfaces. The adsorption/desorption isotherms showed that non-electrostatic adsorption was the main mechanism responsible for arsenate binding to the Oxisol and derived paddy soils, representing 91.42-94.65% of the adsorption capacities. Further studies revealed that arsenate adsorption was greatly inhibited by increasing suspension pH and incorporation of phosphate. Copyright © 2017 Elsevier Ltd. All rights reserved.

New findings on the influence of carbon surface curvature on energetics of benzene adsorption from aqueous solutions

NASA Astrophysics Data System (ADS)

Wiśniewski, Marek; Werengowska-Ciećwierz, Karolina; Terzyk, Artur P.

2015-01-01

Immersional measurements of benzene adsorption form dilute aqueous solutions are reported for the first time together with the measurements of the enthalpy of benzene adsorption. Benzene adsorption from aqueous solution is an exothermic process. Our results show that with the decrease in carbon nanotube diameter the process becomes more exothermic, and the enthalpy of benzene adsorption correlates with the BET surface area and the electrostatic field strength of the tubes. Possible explanations of the results are proposed, and the most probable is that the change in carbon hybridisation with curvature leads to creation of stronger energetically adsorption sites than observed for graphite.

Adsorption of nicotine from aqueous solution onto hydrophobic zeolite type USY

NASA Astrophysics Data System (ADS)

Lazarevic, Natasa; Adnadjevic, Borivoj; Jovanovic, Jelena

2011-07-01

The isothermal adsorption of nicotine from an aqueous solution onto zeolite type USY was investigated. The adsorption isotherms of nicotine onto the zeolite at different temperatures ranging from 298 to 322 K were determined. It was found that the adsorption isotherms can be described by the model of Freundlich adsorption isotherm. Based on the adsorption isotherms the changes of adsorption heat, free energy and entropy with adsorption degree were determined. The determined decrease of adsorption heat with adsorption degree can be explained by the presence of the adsorption centers of different energy and concentration on interface of zeolite-nicotine solution. It was found that the probability function of density distribution of the heat of adsorption (DDF) has exponential form. It was concluded that the possibility of fitting the adsorption isotherms of nicotine onto the zeolite by Freundlich adsorption isotherm was a direct consequence of that. The determined increase in entropy with the increase in adsorption degree can be explained with the change of phase state of adsorbed nicotine.

Adsorption Characteristics of Pb(2+) onto Wine Lees-Derived Biochar.

PubMed

Zhu, Qihong; Wu, Jun; Wang, Lilin; Yang, Gang; Zhang, Xiaohong

2016-08-01

Biochar has great advantages in soil amendment and polluted soil remediation. Herein, the pore and adsorption properties of wine lees-derived biochar were explored. Specifically, the adsorption isotherm and kinetics of Pb(2+) onto wine lees-derived biochar were examined. Experimental results revealed that wine lees-derived biochar featured large specific surface area and total pore volume, and high contents of -COOH and -OH on its surface. Adsorption of Pb(2+) onto wine lees-derived biochar proceeded via a multilayer adsorption mechanism, as described by the Freundlich adsorption model. Adsorption kinetics followed the Lagergren pseudo-second-order kinetics model; adsorption equilibrium was achieved within 30-60 min. Furthermore, the effect of solution pH on the adsorption of Pb(2+) was investigated. Within the studied pH range of 3-6, the adsorption capacity increased with increasing pH. Under established optimized conditions, wine lees-derived biochar achieved a Pb(2+) adsorption capacity of 79.12 mg/g.

Adsorption-desorption behavior of atrazine on agricultural soils in China.

PubMed

Yue, Lin; Ge, ChengJun; Feng, Dan; Yu, Huamei; Deng, Hui; Fu, Bomin

2017-07-01

Adsorption and desorption are important processes that affect atrazine transport, transformation, and bioavailability in soils. In this study, the adsorption-desorption characteristics of atrazine in three soils (laterite, paddy soil and alluvial soil) were evaluated using the batch equilibrium method. The results showed that the kinetics of atrazine in soils was completed in two steps: a "fast" adsorption and a "slow" adsorption and could be well described by pseudo-second-order model. In addition, the adsorption equilibrium isotherms were nonlinear and were well fitted by Freundlich and Langmuir models. It was found that the adsorption data on laterite, and paddy soil were better fitted by the Freundlich model; as for alluvial soil, the Langmuir model described it better. The maximum atrazine sorption capacities ranked as follows: paddy soil>alluvial soil>laterite. Results of thermodynamic calculations indicated that atrazine adsorption on three tested soils was spontaneous and endothermic. The desorption data showed that negative hysteresis occurred. Furthermore, lower solution pH value was conducive to the adsorption of atrazine in soils. The atrazine adsorption in these three tested soils was controlled by physical adsorption, including partition and surface adsorption. At lower equilibrium concentration, the atrazine adsorption process in soils was dominated by surface adsorption; while with the increase of equilibrium concentration, partition was predominant. Copyright © 2016. Published by Elsevier B.V.

Effects of hydration and oxygen vacancy on CO2 adsorption and activation on beta-Ga2O3(100).

PubMed

Pan, Yun-xiang; Liu, Chang-jun; Mei, Donghai; Ge, Qingfeng

2010-04-20

The effects of hydration and oxygen vacancy on CO(2) adsorption on the beta-Ga(2)O(3)(100) surface have been studied using density functional theory slab calculations. Adsorbed CO(2) is activated on the dry perfect beta-Ga(2)O(3)(100) surface, resulting in a carbonate species. This adsorption is slightly endothermic, with an adsorption energy of 0.07 eV. Water is preferably adsorbed molecularly on the dry perfect beta-Ga(2)O(3)(100) surface with an adsorption energy of -0.56 eV, producing a hydrated perfect beta-Ga(2)O(3)(100) surface. Adsorption of CO(2) on the hydrated surface as a carbonate species is also endothermic, with an adsorption energy of 0.14 eV, indicating a slightly repulsive interaction when H(2)O and CO(2) are coadsorbed. The carbonate species on the hydrated perfect surface can be protonated by the coadsorbed H(2)O to a bicarbonate species, making the CO(2) adsorption exothermic, with an adsorption energy of -0.13 eV. The effect of defects on CO(2) adsorption and activation has been examined by creating an oxygen vacancy on the dry beta-Ga(2)O(3)(100) surface. The formation of an oxygen vacancy is endothermic, by 0.34 eV, with respect to a free O(2) molecule in the gas phase. Presence of the oxygen vacancy promoted the adsorption and activation of CO(2). In the most stable CO(2) adsorption configuration on the dry defective beta-Ga(2)O(3)(100) surface with an oxygen vacancy, one of the oxygen atoms of the adsorbed CO(2) occupies the oxygen vacancy site, and the CO(2) adsorption energy is -0.31 eV. Water favors dissociative adsorption at the oxygen vacancy site on the defective surface. This process is spontaneous, with a reaction energy of -0.62 eV. These results indicate that, when water and CO(2) are present in the adsorption system simultaneously, water will compete with CO(2) for the oxygen vacancy sites and impact CO(2) adsorption and conversion negatively.

Dispersion stability of a ceramic glaze achieved through ionic surfactant adsorption.

PubMed

Panya, Preecha; Arquero, Orn-anong; Franks, George V; Wanless, Erica J

2004-11-01

The adsorption of cetylpyridinium chloride (CPC) and sodium dodecylbenzenesulfonate (SDBS) onto a ceramic glaze mixture composed of limestone, feldspar, quartz, and kaolin has been investigated. Both adsorption isotherms and the average particle zeta potential have been studied in order to understand the suspension stability as a function of pH, ionic strength, and surfactant concentration. The adsorption of small amounts of cationic CPC onto the primarily negatively charged surfaces of the particles at pH 7 and 9 results in strong attraction and flocculation due to hydrophobic interactions. At higher surfactant concentrations a zeta potential of more than +60 mV results from the bilayered adsorbed surfactant, providing stability at salt concentrations < or = 0.01 M. At 0.1 M salt poor stability results despite substantial zeta potential values. Three mechanisms for SDBS adsorption have been identified. When anionic SDBS monomers either adsorb by electrostatic interactions with the few positive surface sites at high pH or adsorb onto like charged negative surface sites due to dispersion or hydrophobic interactions, the magnitude of the negative zeta potential increases slightly. At pH 9 this increase is enough to promote stability with an average zeta potential of more than -55 mV, whereas at pH 7 the zeta potential is lower at about -45 mV. The stability of suspensions at pH 7 is additionally due to steric repulsion caused by the adsorption of thick layers of neutrally charged Ca(DBS)2 complexes created when the surfactant interacts with dissolved calcium ions from the calcium carbonate component.

NO adsorption on ice at low concentrations

Treesearch

Richard A. Sommerfeld; Martha H. Conklin; S. Kay Laird

1992-01-01

To better understand the properties of ice surfaces at different temperatures, the adsorption of a relatively insoluble gas, NO, was studied using a continuous-flow column experiment. Adsorption isotherms for NO on the surface of ice were measured for a temperature range of-1 to -70°C and a concentration range of 10 to 250 ppbv. Very little adsorption was measured;...

Electrical swing adsorption gas storage and delivery system

DOEpatents

Judkins, Roddie R.; Burchell, Timothy D.

1999-01-01

Systems and methods for electrical swing natural gas adsorption are described. An apparatus includes a pressure vessel; an electrically conductive gas adsorptive material located within the pressure vessel; and an electric power supply electrically connected to said adsorptive material. The adsorptive material can be a carbon fiber composite molecular sieve (CFCMS). The systems and methods provide advantages in that both a high energy density and a high ratio of delivered to stored gas are provided.

Statistical inference in single molecule measurements of protein adsorption

NASA Astrophysics Data System (ADS)

Armstrong, Megan J.; Tsitkov, Stanislav; Hess, Henry

2018-02-01

Significant effort has been invested into understanding the dynamics of protein adsorption on surfaces, in particular to predict protein behavior at the specialized surfaces of biomedical technologies like hydrogels, nanoparticles, and biosensors. Recently, the application of fluorescent single molecule imaging to this field has permitted the tracking of individual proteins and their stochastic contribution to the aggregate dynamics of adsorption. However, the interpretation of these results is complicated by (1) the finite time available to observe effectively infinite adsorption timescales and (2) the contribution of photobleaching kinetics to adsorption kinetics. Here, we perform a protein adsorption simulation to introduce specific survival analysis methods that overcome the first complication. Additionally, we collect single molecule residence time data from the adsorption of fibrinogen to glass and use survival analysis to distinguish photobleaching kinetics from protein adsorption kinetics.

The adsorption of 1,3-butadiene on Pd/Ni multilayers: The interplay between spin polarization and chemisorption strength

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gomez, Guillermina; Belelli, Patricia G., E-mail: pbelelli@plapiqui.edu.a; Cabeza, Gabriela F.

2010-12-15

The adsorption of 1,3-butadiene (BD) on the Pd/Ni(1 1 1) multilayers has been studied using the VASP method in the framework of the density functional theory (DFT). The adsorption on two different configurations of the Pd{sub n}/Ni{sub m}(1 1 1) systems were considered. The most stable adsorption sites are dependent on the substrate composition and on the inclusion or not of spin polarization. On Pd{sub 1}Ni{sub 3}(1 1 1) surface, di-{pi}-cis and 1,2,3,4-tetra-{sigma} adsorption structures are the most stable for non-spin polarized (NSP) and spin polarized (SP) levels of calculation, respectively. Conversely, on Pd{sub 3}Ni{sub 1}(1 1 1) surface, themore » 1,2,3,4-tetra-{sigma} adsorption structure is the most stable for both NSP and SP levels, respectively. The magnetization of the Pd atoms strongly modifies the adsorption energy of BD and its most stable adsorption mode. On the other hand, as a consequence of BD adsorption, the Pd magnetization decreases. The smaller adsorption energies of BD and 1-butene on the Pd{sub 1}Ni{sub 3}(1 1 1) surface than on Pd(1 1 1) can be associated to the strained Pd overlayer deposited on Ni(1 1 1). -- Graphical Abstract: The adsorption of 1,3-butadiene on Pd/Ni(1 1 1) multilayers was theoretically studied. The most stable adsorption site depends on the substrate composition and on the inclusion of spin polarization. Display Omitted« less

A First Principles Study of H2 Adsorption on LaNiO3(001) Surfaces

PubMed Central

Pan, Changchang; Chen, Yuhong; Wu, Na; Zhang, Meiling; Yuan, Lihua; Zhang, Cairong

2017-01-01

The adsorption of H2 on LaNiO3 was investigated using density functional theory (DFT) calculations. The adsorption sites, adsorption energy, and electronic structure of LaNiO3(001)/H2 systems were calculated and indicated through the calculated surface energy that the (001) surface was the most stable surface. By looking at optimized structure, adsorption energy and dissociation energy, we found that there were three types of adsorption on the surface. First, H2 molecules completely dissociate and then tend to bind with the O atoms, forming two –OH bonds. Second, H2 molecules partially dissociate with the H atoms bonding to the same O atom to form one H2O molecule. These two types are chemical adsorption modes; however, the physical adsorption of H2 molecules can also occur. When analyzing the electron structure of the H2O molecule formed by the partial dissociation of the H2 molecule and the surface O atom, we found that the interaction between H2O and the (001) surface was weaker, thus, H2O was easier to separate from the surface to create an O vacancy. On the (001) surface, a supercell was constructed to accurately study the most stable adsorption site. The results from analyses of the charge population; electron localization function; and density of the states indicated that the dissociated H and O atoms form a typical covalent bond and that the interaction between the H2 molecule and surface is mainly due to the overlap-hybridization among the H 1s, O 2s, and O 2p states. Therefore, the conductivity of LaNiO3(001)/H2 is stronger after adsorption and furthermore, the conductivity of the LaNiO3 surface is better than that of the LaFeO3 surface. PMID:28772396

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

PubMed

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

2015-12-01

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

Neptunium(V) Adsorption to Bacteria at Low and High Ionic Strength

NASA Astrophysics Data System (ADS)

Ams, D.; Swanson, J. S.; Reed, D. T.

2010-12-01

strength effects as the electronic double layer is compressed with increasing ionic strength. These results further highlight the importance of electrostatic interactions in the adsorption process between dissolved metals and bacterial surfaces. This work expands the understanding of actinide-bacteria adsorption phenomena to high ionic strength environmental conditions that are relevant as an aid to predicting Np(V) fate and transport behavior in areas such as the vicinity of salt-based nuclear waste repositories and high ionic-strength groundwaters at DOE sites.

Water adsorption on a liquid surface.

PubMed

Lovelock, Kevin R J; Smith, Emily F; Deyko, Alexey; Villar-Garcia, Ignacio J; Licence, Peter; Jones, Robert G

2007-12-14

Monolayer adsorption of water onto an ionic liquid in ultra-high vacuum has been demonstrated, revealing a heat of adsorption which exceeds the heat of absorption into the bulk liquid by approximately 40 kJ mol(-1).

Effects of pH and phosphate on glyphosate adsorption to Argentina soils.

NASA Astrophysics Data System (ADS)

De Geronimo, Eduardo; Aparicio, Virginia; Costa, José Luis

2017-04-01

Glyphosate is a non-selective, post-emergence herbicide that is widely used in Argentina. Due to the similar molecular structures, glyphosate and phosphate compete for the same adsorption sites in soil. Soil pH has a strong influence in glyphosate and phosphate adsorption since it modifies the net charge of the molecules and, consequently, the force of the electrostatic interaction between these molecules and soil components. Glyphosate adsorption generally decreases as the soil pH was increased, although there were exceptions. In this work, we study the effects of pH and the presence of phosphate on the adsorption of glyphosate on six different types of Argentina soils. Batch equilibrium technique was employed to study the adsorption of glyphosate onto soils at different pH values (from 3 to 9) and phosphate content (0.5 and 1 mM). Stepwise multiple linear regression analysis was applied to obtain a relationship between the sorption parameters and soil properties. The results indicated that Freundlich equations used to simulate glyphosate adsorption isotherms gave high correlation coefficients with Kf values range from 24.9 to 397.4. Clay contents and soil pH were found to be the most significant soil factors affecting the glyphosate adsorption process. The presence of phosphate significantly decreased the adsorption of glyphosate to soils. The Kf values obtained for all six soils decreased a 40% at 0.5 mM of phosphate and a 55% at 1 mM of phosphate. On the other hand, the affinity parameters of glyphosate to soils varied with changes in pH. A general trend of decrease in glyphosate adsorption with increase in pH was observed for all six studied soils. In turn, there appears to be a maximum glyphosate adsorption at pH close to 6 for most soils when the net charge of the molecule at this pH was approximately -1.7.

Response surface modeling of boron adsorption from aqueous solution by vermiculite using different adsorption agents: Box-Behnken experimental design.

PubMed

Demirçivi, Pelin; Saygılı, Gülhayat Nasün

2017-07-01

In this study, a different method was applied for boron removal by using vermiculite as the adsorbent. Vermiculite, which was used in the experiments, was not modified with adsorption agents before boron adsorption using a separate process. Hexadecyltrimethylammonium bromide (HDTMA) and Gallic acid (GA) were used as adsorption agents for vermiculite by maintaining the solid/liquid ratio at 12.5 g/L. HDTMA/GA concentration, contact time, pH, initial boron concentration, inert electrolyte and temperature effects on boron adsorption were analyzed. A three-factor, three-level Box-Behnken design model combined with response surface method (RSM) was employed to examine and optimize process variables for boron adsorption from aqueous solution by vermiculite using HDTMA and GA. Solution pH (2-12), temperature (25-60 °C) and initial boron concentration (50-8,000 mg/L) were chosen as independent variables and coded x 1 , x 2 and x 3 at three levels (-1, 0 and 1). Analysis of variance was used to test the significance of variables and their interactions with 95% confidence limit (α = 0.05). According to the regression coefficients, a second-order empirical equation was evaluated between the adsorption capacity (q i ) and the coded variables tested (x i ). Optimum values of the variables were also evaluated for maximum boron adsorption by vermiculite-HDTMA (HDTMA-Verm) and vermiculite-GA (GA-Verm).

Significance of Graphitic Surfaces in Aurodicyanide Adsorption by Activated Carbon: Experimental and Computational Approach

NASA Astrophysics Data System (ADS)

Bhattacharyya, Dhiman; Depci, Tolga; Prisbrey, Keith; Miller, Jan D.

Despite tremendous developments in industrial use of activated carbon (AC) for gold adsorption, specific aurodicyanide [Au(CN)2-] adsorption sites on the carbon have intrigued researchers. The graphitic structure of AC has been well established. Previously radiochemical and now, XPS and Raman characterizations have demonstrated higher site-specific gold adsorption on graphitic edges. Morphological characterizations have revealed the presence of slit-pores (5-10 Å). Molecular-dynamics-simulation (MDS) performed on graphitic slit-pores illustrated gold-cyanide ion-pair preferentially adsorbs on edges. Ab-initio simulations predicted lower barrier for electron sharing in pores with aurodic yanide, indicating tighter bonding than graphitic surface and was well supported by Gibbs energy calculations too. Interaction energy as function of the separation distance indicated tighter bonding of gold cyanide to the graphite edges than water molecules. Selective adsorption of aurodicyanide ion-pair seems to be related to low polarity of gold complex and its accommodation at graphitic edges.

Adsorption orientations and immunological recognition of antibodies on graphene

NASA Astrophysics Data System (ADS)

Vilhena, J. G.; Dumitru, A. C.; Herruzo, Elena T.; Mendieta-Moreno, Jesús I.; Garcia, Ricardo; Serena, P. A.; Pérez, Rubén

2016-07-01

Large-scale molecular dynamics (MD) simulations and atomic force microscopy (AFM) in liquid are combined to characterize the adsorption of Immunoglobulin G (IgG) antibodies over a hydrophobic surface modeled with a three-layer graphene slab. We consider explicitly the water solvent, simulating systems with massive sizes (up to 770 000 atoms), for four different adsorption orientations. Protocols based on steered MD to speed up the protein diffusion stage and to enhance the dehydration process are combined with long simulation times (>150 ns) in order to make sure that the final adsorption states correspond to actual stable configurations. Our MD results and the AFM images demonstrate that the IgG antibodies are strongly adsorbed, do not unfold, and retain their secondary and tertiary structures upon deposition. Statistical analysis of the AFM images shows that many of the antibodies adopt vertical orientations, even at very small coverages, which expose at least one Fab binding site for recognition events. Single molecule force spectroscopy experiments demonstrate the immunological response of the deposited antibodies by recognizing its specific antigens. The above properties together with the strong anchoring and preservation of the secondary structure, make graphene an excellent candidate for the development of immunosensors.Large-scale molecular dynamics (MD) simulations and atomic force microscopy (AFM) in liquid are combined to characterize the adsorption of Immunoglobulin G (IgG) antibodies over a hydrophobic surface modeled with a three-layer graphene slab. We consider explicitly the water solvent, simulating systems with massive sizes (up to 770 000 atoms), for four different adsorption orientations. Protocols based on steered MD to speed up the protein diffusion stage and to enhance the dehydration process are combined with long simulation times (>150 ns) in order to make sure that the final adsorption states correspond to actual stable configurations. Our

Cd and proton adsorption onto bacterial consortia grown from industrial wastes and contaminated geologic settings.

PubMed

Borrok, David M; Fein, Jeremy B; Kulpa, Charles F

2004-11-01

To model the effects of bacterial metal adsorption in contaminated environments, results from metal adsorption experiments involving individual pure stains of bacteria must be extrapolated to systems in which potentially dozens of bacterial species are present. This extrapolation may be made easier because bacterial consortia from natural environments appear to exhibit similar metal binding properties. However, bacteria that thrive in highly perturbed contaminated environments may exhibit significantly different adsorptive behavior. Here we measure proton and Cd adsorption onto a range of bacterial consortia grown from heavily contaminated industrial wastes, groundwater, and soils. We model the results using a discrete site surface complexation approach to determine binding constants and site densities for each consortium. The results demonstrate that bacterial consortia from different contaminated environments exhibit a range of total site densities (approximately a 3-fold difference) and Cd-binding constants (approximately a 10-fold difference). These ranges for Cd binding constants may be small enough to suggest that bacteria-metal adsorption in contaminated environments can be described using relatively few "averaged" bacteria-metal binding constants (in conjunction with the necessary binding constants for competing surfaces and ligands). However, if additional precision is necessary, modeling parameters must be developed separately for each contaminated environment of interest.

Phosphorus recovery using pelletized adsorptive materials ...

EPA Pesticide Factsheets

Phosphorous (P) is one of the essential nutrients for growth and is generally the most limiting nutrient since, it cannot be fixed from the atmosphere. Methods for recovering phosphorous from water systems already exist, but advances are being made to find a more economic, efficient, effective and easy to use method that can allow for reuse of the recovered P. One area of study is in adsorption, which involves finding the best material for adsorption of phosphorous from water and for releasing it back into the environment through desorption or leaching. The goal of this research was to first optimize the capacity for a pelletized adsorptive material that was synthesized with varying amounts of a binder material from 0-20 % and then to study recovering the phosphate for reuse. The pelletized materials were studied through kinetics experiments as well as isotherm experiments to gain insight into the adsorption capacity and mechanism. Following successful adsorption, a simple leaching study was conducted to see how much phosphate would be released back into water without any added desorption aid. Desorption was then studied by changing the pH of solution. Presenting my thesis work with a poster at ACS.

Macroscopic and Microscopic Investigation of U(VI) and Eu(III) Adsorption on Carbonaceous Nanofibers.

PubMed

Sun, Yubing; Wu, Zhen-Yu; Wang, Xiangxue; Ding, Congcong; Cheng, Wencai; Yu, Shu-Hong; Wang, Xiangke

2016-04-19

The adsorption mechanism of U(VI) and Eu(III) on carbonaceous nanofibers (CNFs) was investigated using batch, IR, XPS, XANES, and EXAFS techniques. The pH-dependent adsorption indicated that the adsorption of U(VI) on the CNFs was significantly higher than the adsorption of Eu(III) at pH < 7.0. The maximum adsorption capacity of the CNFs calculated from the Langmuir model at pH 4.5 and 298 K for U(VI) and Eu(III) were 125 and 91 mg/g, respectively. The CNFs displayed good recyclability and recoverability by regeneration experiments. Based on XPS and XANES analyses, the enrichment of U(VI) and Eu(III) was attributed to the abundant adsorption sites (e.g., -OH and -COOH groups) of the CNFs. IR analysis further demonstrated that -COOH groups were more responsible for U(VI) adsorption. In addition, the remarkable reducing agents of the R-CH2OH groups were responsible for the highly efficient adsorption of U(VI) on the CNFs. The adsorption mechanism of U(VI) on the CNFs at pH 4.5 was shifted from inner- to outer-sphere surface complexation with increasing initial concentration, whereas the surface (co)precipitate (i.e., schoepite) was observed at pH 7.0 by EXAFS spectra. The findings presented herein play an important role in the removal of radionuclides on inexpensive and available carbon-based nanoparticles in environmental cleanup applications.

Caffeine adsorption of montmorillonite in coffee extracts.

PubMed

Shiono, Takashi; Yamamoto, Kenichiro; Yotsumoto, Yuko; Yoshida, Aruto

2017-08-01

The growth in health-conscious consumers continues to drive the demand for a wide variety of decaffeinated beverages. We previously developed a new technology using montmorillonite (MMT) in selective decaffeination of tea extract. This study evaluated and compared decaffeination of coffee extract using MMT and activated carbon (AC). MMT adsorbed caffeine without significant adsorption of caffeoylquinic acids (CQAs), feruloylquinic acids (FQAs), dicaffeoylquinic acids (di-CQAs), or caffeoylquinic lactones (CQLs). AC adsorbed caffeine, chlorogenic acids (CGAs) and CQLs simultaneously. The results suggested that the adsorption selectivity for caffeine in coffee extract is higher in MMT than AC. The caffeine adsorption isotherms of MMT in coffee extract fitted well to the Langmuir adsorption model. The adsorption properties in coffee extracts from the same species were comparable, regardless of roasting level and locality of growth. Our findings suggest that MMT is a useful adsorbent in the decaffeination of a wide range of coffee extracts.

Adsorption and desorption for dynamics transport of hexavalent chromium Cr(Ⅵ) in soil column

NASA Astrophysics Data System (ADS)

Tong, J.

2017-12-01

Batch experiments have been carried out to study the adsorption of heavy metals in soils, and the migration and transformation of hexavalent chromium Cr(Ⅵ) in the soil of a vegetable base were studied by dynamic adsorption and desorption soil column experiments. The aim of this study was to investigate the effect of initial concentration and pH value on the adsorption process of Cr(Ⅵ). Breakthrough curve were used to evaluate the capacity of Cr(Ⅵ) adsorption in soil columns. The results show that the higher the initial concentration, the worse the adsorption capacity of Cr(Ⅵ). The adsorption of Cr(Ⅵ) was strongly sensitive to pH value. The capacity of Cr(Ⅵ) adsorption is maximized at very low pH value. This may be due to changes in pH that cause a series of complex reactions in Cr(Ⅵ). In a strongly acidic environment, the reaction of Cr(Ⅵ) with hydrogen ions is accompanied by the formation of Cr3+, which reacts with the soil free iron-aluminum oxide to produce hydroxide in the soil. The results of the desorption experiments indicate that Cr(Ⅵ) is more likely to leach from this soil, but if the eluent is strong acid solution, the leaching process will be slow and persistent. The program CXTFIT was used to fit the breakthrough curve to estimate parameters. The results of the calculation of the dispersion coefficient (D) can be obtained by this program. The two-site model fit the breakthrough curve data of Cr(Ⅵ) well, and the parameters calculated by CXTFIT can be used to explain the behavior of Cr(Ⅵ) migration and transformation in soil columns. When pH=2, the retardation factor (R) reach at 79.71 while the value of the R is generally around 10 in other experiments. The partitioning coefficient β shows that more than half of the adsorption sites are rate-limited in this adsorption process and non-equilibrium effects the Cr(Ⅵ) transport process in this soil.

Adsorption of lead onto smectite from aqueous solution.

PubMed

Mhamdi, M; Galai, H; Mnasri, N; Elaloui, E; Trabelsi-Ayadi, M

2013-03-01

The purpose of this research is to study the effect of a new method of adsorption using membrane filtration to determine the maximum amount of lead adsorbed by clay and investigate the behavior of the clay after adsorption of the said metal. Treatment of wastewater contaminated with heavy metals depends on the characteristics of the effluent, the amount of final discharge, the cost of treatment, and the compatibility of the treatment process. The process of adsorption of heavy metals by clays may be a simple, selective, and economically viable alternative to the conventional physical-chemical treatment. This is justified by the importance of the surface developed by this material, the presence of negative charges on the said surface, the possibility of ion exchange taking place, and its wide availability in nature. The removal of lead from wastewater was studied by using the adsorption technique and using clay as the adsorbent. A method was optimized for adsorption through a membrane approaching natural adsorption. This new method is simple, selective, and the lead adsorption time is about 3 days. The various properties of clay were determined. It was observed that the cation exchange capacity of the clay was 56 meq/100 g of hydrated clay for the raw sample and 82 meq/100 g for the purified sample. The total surface area determined by the methylene blue method was equal to 556 and 783 m(2)/g for the raw and purified samples, respectively. The adsorption kinetics depends on several parameters. The Pb(II) clay, obeys the Langmuir, Freundlich, and the Elovich adsorption isotherms with high regression coefficients. The use of this adsorbent notably decreases the cost of treatment. It was concluded that clay shows a strong adsorption capacity on Pb(II), the maximum interaction occurring with purified clay treated at high concentration of lead. It is proposed that this adsorption through a membrane be extended for the treatment of effluents containing other metals.

Electrical swing adsorption gas storage and delivery system

DOEpatents

Judkins, R.R.; Burchell, T.D.

1999-06-15

Systems and methods for electrical swing natural gas adsorption are described. An apparatus includes a pressure vessel; an electrically conductive gas adsorptive material located within the pressure vessel; and an electric power supply electrically connected to said adsorptive material. The adsorptive material can be a carbon fiber composite molecular sieve (CFCMS). The systems and methods provide advantages in that both a high energy density and a high ratio of delivered to stored gas are provided. 5 figs.

Adsorption mechanisms and impact factors of oxytetracycline on activated sludge

NASA Astrophysics Data System (ADS)

Xiancai, Song; Dongfang, Liu; Lejun, Zhao

2017-03-01

The adsorption mechanisms and the effect of Oxytetracycline (OTC) onto activated sludge were studied. The results show that the adsorption of Oxytetracycline (OTC) onto activated sludge was coincident with the Pseudo-second-order kinetic model which suggested that chemical adsorption mechanism was dominant. The influences including pH and metal ions on the OTC were examined. It was demonstrated that the adsorption process was highly pH-dependant, which indicate that cationic exchange mechanisms may play an important role in the adsorption process. Na+, K+, Ca2+, Mg2+ and Cd2+ ions more or less inhibited the adsorption of OTC on activated sludge while Cu2+ enhanced the adsorption ability. The phenomenon may reflect the result that a surface complexation mechanism could involved in the adsorption.

A CONTINUUM HARD-SPHERE MODEL OF PROTEIN ADSORPTION

PubMed Central

Finch, Craig; Clarke, Thomas; Hickman, James J.

2012-01-01

Protein adsorption plays a significant role in biological phenomena such as cell-surface interactions and the coagulation of blood. Two-dimensional random sequential adsorption (RSA) models are widely used to model the adsorption of proteins on solid surfaces. Continuum equations have been developed so that the results of RSA simulations can be used to predict the kinetics of adsorption. Recently, Brownian dynamics simulations have become popular for modeling protein adsorption. In this work a continuum model was developed to allow the results from a Brownian dynamics simulation to be used as the boundary condition in a computational fluid dynamics (CFD) simulation. Brownian dynamics simulations were used to model the diffusive transport of hard-sphere particles in a liquid and the adsorption of the particles onto a solid surface. The configuration of the adsorbed particles was analyzed to quantify the chemical potential near the surface, which was found to be a function of the distance from the surface and the fractional surface coverage. The near-surface chemical potential was used to derive a continuum model of adsorption that incorporates the results from the Brownian dynamics simulations. The equations of the continuum model were discretized and coupled to a CFD simulation of diffusive transport to the surface. The kinetics of adsorption predicted by the continuum model closely matched the results from the Brownian dynamics simulation. This new model allows the results from mesoscale simulations to be incorporated into micro- or macro-scale CFD transport simulations of protein adsorption in practical devices. PMID:23729843

Multilayer adsorption of Cu(II) and Cd(II) over Brazilian Orchid Tree (Pata-de-vaca) and its adsorptive properties

NASA Astrophysics Data System (ADS)

Jorgetto, Alexandre de O.; da Silva, Adrielli C. P.; Wondracek, Marcos H. P.; Silva, Rafael I. V.; Velini, Edivaldo D.; Saeki, Margarida J.; Pedrosa, Valber A.; Castro, Gustavo R.

2015-08-01

Through very simple and inexpensive processes, pata-de-vaca leaves were turned into a powder and applied as an adsorbent for the uptake of Cu(II) and Cd(II) from water. The material was characterized through SEM, EDX, FTIR and surface area measurement. The material had its point of zero charge determined (5.24), and its adsorption capacity was evaluated as a function of time, pH and metal concentration. The material presented fast adsorption kinetics, reaching adsorption equilibrium in less than 5 min and it had a good correlation with the pseudo-second order kinetic model. Optimum pH for the adsorption of Cu(II) and Cd(II) were found to be in the range from 4 to 5, approximately. In the experiment as a function of the analyte concentration, analogously to gas adsorption, the material presented a type II isotherm, indicating the formation of multilayers for both species. Such behavior was explained with basis in the alternation between cations and anions over the material's surface, and the maximum adsorption capacity, considering the formation of the multilayers were found to be 0.238 mmol L-1 for Cu(II) and 0.113 mmol L-1 for Cd(II).

Adsorption and flocculation by polymers and polymer mixtures.

PubMed

Gregory, John; Barany, Sandor

2011-11-14

Polymers of various types are in widespread use as flocculants in several industries. In most cases, polymer adsorption is an essential prerequisite for flocculation and kinetic aspects are very important. The rates of polymer adsorption and of re-conformation (relaxation) of adsorbed chains are key factors that influence the performance of flocculants and their mode of action. Polyelectrolytes often tend to adopt a rather flat adsorbed configuration and in this state their action is mainly through charge effects, including 'electrostatic patch' attraction. When the relaxation rate is quite low, particle collisions may occur while the adsorbed chains are still in an extended state and flocculation by polymer bridging may occur. These effects are now well understood and supported by much experimental evidence. In recent years there has been considerable interest in the use of multi-component flocculants, especially dual-polymer systems. In the latter case, there can be significant advantages over the use of single polymers. Despite some complications, there is a broad understanding of the action of dual polymer systems. In many cases the sequence of addition of the polymers is important and the pre-adsorbed polymer can have two important effects: providing adsorption sites for the second polymer or causing a more extended adsorbed conformation as a result of 'site blocking'. Copyright © 2011 Elsevier B.V. All rights reserved.

Use of hydrophilic polymer coatings for control of electroosmosis and protein adsorption

NASA Technical Reports Server (NTRS)

Harris, J. Milton

1987-01-01

The purpose of this project was to examine the utility of polyethylene glycol (PEG) and dextran coatings for control of electroosmosis and protein adsorption; electroosmosis is an important, deleterious process affecting electrophoretic separations, and protein adsorption is a factor which needs to be controlled during protein crystal growth to avoid multiple nucleation sites. Performance of the project required use of X-ray photoelectron spectroscopy to refine previously developed synthetic methods. The results of this spectroscopic examination are reported. Measurements of electroosmotic mobility of charged particles in appropriately coated capillaries reveals that a new, one-step route to coating capillaries gives a surface in which electroosmosis is dramatically reduced. Similarly, both PEG and dextran coatings were shown by protein adsorption measurements to be highly effective at reducing protein adsorption on solid surfaces. These results should have impact on future low-g electrophoretic and protein crystal growth experiments.

A pressure-amplifying framework material with negative gas adsorption transitions.

PubMed

Krause, Simon; Bon, Volodymyr; Senkovska, Irena; Stoeck, Ulrich; Wallacher, Dirk; Többens, Daniel M; Zander, Stefan; Pillai, Renjith S; Maurin, Guillaume; Coudert, François-Xavier; Kaskel, Stefan

2016-04-21

Adsorption-based phenomena are important in gas separations, such as the treatment of greenhouse-gas and toxic-gas pollutants, and in water-adsorption-based heat pumps for solar cooling systems. The ability to tune the pore size, shape and functionality of crystalline porous coordination polymers--or metal-organic frameworks (MOFs)--has made them attractive materials for such adsorption-based applications. The flexibility and guest-molecule-dependent response of MOFs give rise to unexpected and often desirable adsorption phenomena. Common to all isothermal gas adsorption phenomena, however, is increased gas uptake with increased pressure. Here we report adsorption transitions in the isotherms of a MOF (DUT-49) that exhibits a negative gas adsorption; that is, spontaneous desorption of gas (methane and n-butane) occurs during pressure increase in a defined temperature and pressure range. A combination of in situ powder X-ray diffraction, gas adsorption experiments and simulations shows that this adsorption behaviour is controlled by a sudden hysteretic structural deformation and pore contraction of the MOF, which releases guest molecules. These findings may enable technologies using frameworks capable of negative gas adsorption for pressure amplification in micro- and macroscopic system engineering. Negative gas adsorption extends the series of counterintuitive phenomena such as negative thermal expansion and negative refractive indices and may be interpreted as an adsorptive analogue of force-amplifying negative compressibility transitions proposed for metamaterials.

Carbon dioxide separation using adsorption with steam regeneration

DOEpatents

Elliott, Jeannine Elizabeth; Copeland, Robert James; Leta, Daniel P.; McCall, Patrick P.; Bai, Chuansheng; DeRites, Bruce A.

2016-11-29

A process for separating a carbon dioxide from a gas stream is disclosed. The process can include passing the gas stream over a sorbent that adsorbs the carbon dioxide by concentration swing adsorption and adsorptive displacement. The sorbent can be regenerated and the carbon dioxide recaptured by desorbing the carbon dioxide from the sorbent using concentration swing adsorption and desorptive displacement. A carbon dioxide separation system is also disclosed. Neither the system nor the process rely on temperature swing or pressure swing adsorption.

Diffusion Influenced Adsorption Kinetics.

PubMed

Miura, Toshiaki; Seki, Kazuhiko

2015-08-27

When the kinetics of adsorption is influenced by the diffusive flow of solutes, the solute concentration at the surface is influenced by the surface coverage of solutes, which is given by the Langmuir-Hinshelwood adsorption equation. The diffusion equation with the boundary condition given by the Langmuir-Hinshelwood adsorption equation leads to the nonlinear integro-differential equation for the surface coverage. In this paper, we solved the nonlinear integro-differential equation using the Grünwald-Letnikov formula developed to solve fractional kinetics. Guided by the numerical results, analytical expressions for the upper and lower bounds of the exact numerical results were obtained. The upper and lower bounds were close to the exact numerical results in the diffusion- and reaction-controlled limits, respectively. We examined the validity of the two simple analytical expressions obtained in the diffusion-controlled limit. The results were generalized to include the effect of dispersive diffusion. We also investigated the effect of molecular rearrangement of anisotropic molecules on surface coverage.

A chemical equilibrium model for metal adsorption onto bacterial surfaces

NASA Astrophysics Data System (ADS)

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

1997-08-01

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

Wide-range and accurate modeling of linear alkylbenzene sulfonate (LAS) adsorption/desorption on agricultural soil.

PubMed

Oliver-Rodríguez, B; Zafra-Gómez, A; Reis, M S; Duarte, B P M; Verge, C; de Ferrer, J A; Pérez-Pascual, M; Vílchez, J L

2015-11-01

In this paper, rigorous data and adequate models about linear alkylbenzene sulfonate (LAS) adsorption/desorption on agricultural soil are presented, contributing with a substantial improvement over available adsorption works. The kinetics of the adsorption/desorption phenomenon and the adsorption/desorption equilibrium isotherms were determined through batch studies for total LAS amount and also for each homologue series: C10, C11, C12 and C13. The proposed multiple pseudo-first order kinetic model provides the best fit to the kinetic data, indicating the presence of two adsorption/desorption processes in the general phenomenon. Equilibrium adsorption and desorption data have been properly fitted by a model consisting of a Langmuir plus quadratic term, which provides a good integrated description of the experimental data over a wide range of concentrations. At low concentrations, the Langmuir term explains the adsorption of LAS on soil sites which are highly selective of the n-alkyl groups and cover a very small fraction of the soil surface area, whereas the quadratic term describes adsorption on the much larger part of the soil surface and on LAS retained at moderate to high concentrations. Since adsorption/desorption phenomenon plays a major role in the LAS behavior in soils, relevant conclusions can be drawn from the obtained results. Copyright © 2015 Elsevier Ltd. All rights reserved.

Adsorption of xenon and krypton on shales

NASA Technical Reports Server (NTRS)

Podosek, F. A.; Bernatowicz, T. J.; Kramer, F. E.

1981-01-01

A method that uses a mass spectrometer as a manometer is employed in the measurement of Xe and Kr adsorption parameters on shales and related samples, where gas partial pressures were lower than 10 to the -11th atm, corresponding adsorption coverages are only small fractions of a monolayer, and Henry's Law behavior is expected and observed. Results show heats of adsorption in the 2-7 kcal/mol range, and Henry constants at 0-25 C of 1 cu cm STP/g per atmosphere are extrapolated. Although the adsorption properties obtained are variable by sample, the range obtained suggests that shales may be capable of an equilibrium adsorption with modern air high enough to account for a significant fraction of the atmospheric inventory of Xe, and perhaps even of Kr. This effect will nevertheless not account for the factor-of-25 defficiency of atmospheric Xe, in comparison with the planetary gas patterns observed in meteorites.

Adsorption and Photodesorption of CO from Charged Point Defects on TiO 2 (110)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mu, Rentao; Dahal, Arjun; Wang, Zhi-Tao

Adsorption and photodesorption of weakly-bound carbon monoxide, CO, from reduced and hydroxylated rutile TiO2(110) (r- and h- TiO2(110)) at sub-monolayer coverages is studied with atomically-resolved scanning tunneling microscopy (STM) along with ensemble-averaged temperature-programmed desorption (TPD) and angle-resolved photon-stimulated desorption (PSD) at low temperatures ( 50 K). STM data weighted by the concentration of each kind of adsorption sites on r-TiO2(110) give an adsorption probability which is the highest for the bridging oxygen vacancies (VO) and very low for the Ti5c sites closest to VO. Occupancy of the remaining Ti5c sites with CO is significant, but smaller than for VO. Themore » probability distribution for the different adsorption sites corresponds to a very small difference in CO adsorption energies: < 0.02 eV. We also find that UV irradiation stimulates both diffusion and desorption of CO at low temperature. CO photodesorbs primarily from the vacancies with a bi-modal angular distribution. In addition to a major, normal to the surface component, there is a broader cosine component indicating scattering from the surface which likely also leads to photo-stimulated diffusion. Hydroxylation of VO’s does not significantly change the CO PSD yield and angular distribution, indicating that not atomic but rather electronic surface defects are involved in the site-specific PSD process. We suggest that photodesorption can be initiated by recombination of photo-generated holes with excess unpaired electrons localized near the surface point-defect (either VO or bridging hydroxyl), leading to the surface atoms rearrangement and ejection of the weakly-bound CO molecules.« less

Carbon composite lignin-based adsorbents for the adsorption of dyes.

PubMed

Wang, Xiaohong; Jiang, Chenglong; Hou, Bingxia; Wang, Yingying; Hao, Chen; Wu, Jingbo

2018-05-10

Carbon composite lignin-based adsorbent were prepared through hydrothermal method with glucose as carbon source, calcium lignosulfonate and triethylene tetramine as raw materials, respectively. The optimum synthesis conditions were determined by investigating the addition of carbon and triethylene tetramine. The adsorbent was used for the adsorption of azo dyes Congo red and Eriochrome blue black R, and the five factors affecting the adsorption were discussed, including pH of dyes, initial concentration, adsorption time, adsorption temperature and adsorbent dosage. The corresponding adsorption mechanism such as pseudo first order kinetics, pseudo second order kinetics, intraparticle diffusion, Langmuir adsorption isotherm, Freundlich isotherm, Temkin isotherm, Dubinin-Radushkevich adsorption isotherm, thermodynamics were also studied. When the dye concentration is 40 mg L -1 , Congo red and Eriochrome blue black R dye removal rates reach 99%. Moreover, the adsorption process of two kinds of dyes follow the pseudo second order kinetics and the Langmuir adsorption isotherm. Copyright © 2018 Elsevier Ltd. All rights reserved.

A computational study on the energetics and mechanisms for the dissociative adsorption of SiHx(x = 1-4) on W(1 1 1) surface

NASA Astrophysics Data System (ADS)

Lin, Y. H.; Raghunath, P.; Lin, M. C.

2016-01-01

The adsorption and dissociation mechanisms of SiHx(x = 1-4) species on W(1 1 1) surface have been investigated by using the periodic density functional theory with the projector-augmented wave approach. The adsorption of all the species on four surface sites: top (T), bridge (B), shallow (S), and deep (D) sites have been analyzed. For SiH4 on a top site, T-SiH4(a), it is more stable with an adsorption energy of 2.6 kcal/mol. For SiH3, the 3-fold shallow site is most favorable with adsorption energy of 46.0 kcal/mol. For SiH2, its adsorption on a bridge site is most stable with 73.0 kcal/mol binding energy, whereas for SiH and Si the most stable adsorption configurations are on 3-fold deep sites with very high adsorption energies, 111.8 and 134.7 kcal/mol, respectively. The potential energy surfaces for the dissociative adsorption of all SiHx species on the W(1 1 1) surface have been constructed using the CINEB method. The barriers for H-atom migration from SiHx(a) to its neighboring W atoms, preferentially on B-sites, were predicted to be 0.4, 1.0, 4.5 and, 8.0 kcal/mol, respectively, for x = 4, 3, 2, and 1, respectively. The adsorption energy of the H atom on a bridge site on the clean W(1 1 1) surface was predicted to be 65.9 kcal/mol, which was found to be slightly affected by the co-adsorption of SiHx-1 within ± 1 kcal/mol.

Activated Carbon Preparation and Modification for Adsorption

NASA Astrophysics Data System (ADS)

Cao, Yuhe

Butanol is considered a promising, infrastructure-compatible biofuel. Butanol has a higher energy content than ethanol and can be used in conventional gas engines without modifications. Unfortunately, the fermentation pathway for butanol production is restricted by its toxicity to the microbial strains used in the process. Butanol is toxic to the microbes, and this can slow fermentation rates and reduce butanol yields. Gas stripping technology can efficiently remove butanol from the fermentation broth as it is produced, thereby decreasing its inhibitory effects. Traditional butanol separation heavily depends on the energy intensive distillation method. One of the main issues in acetone-butanol-ethanol fermentation is that butanol concentrations in the fermentation broth are low, ranging from 1 to 1.2 percent in weight, because of its toxicity to the microorganisms. Therefore distillation of butanol is even worse than distillation of corn ethanol. Even new separation methods, such as solid- extraction methods involve adding substances, such as polymer resin and zeolite or activated carbon, to biobutanol fermentatioon broth did not achieve energy efficient separation of butanol due to low adsorption selectivity and fouling in broth. Gas-stripping - condensation is another new butanol recovery method, however, the butanol in gas-stripping stream is too low to be condensed without using expensive and energy intensive liquid nitrogen. Adsorption can then be used to recover butanol from the vapor phase. Activated carbon (AC) samples and zeolite were investigated for their butanol vapor adsorption capacities. Commercial activated carbon was modified via hydrothermal H2O2 treatment, and the specific surface area and oxygen-containing functional groups of activated carbon were tested before and after treatment. Hydrothermal H2O 2 modification increased the surface oxygen content, Brunauer-Emmett-Teller surface area, micropore volume, and total pore volume of active carbon

High-throughput screening of small-molecule adsorption in MOF-74

NASA Astrophysics Data System (ADS)

Thonhauser, T.; Canepa, P.

2014-03-01

Using high-throughput screening coupled with state-of-the-art van der Waals density functional theory, we investigate the adsorption properties of four important molecules, H2, CO2, CH4, and H2O in MOF-74-  with  = Be, Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Zr, Nb, Ru, Rh, Pd, La, W, Os, Ir, and Pt. We show that high-throughput techniques can aid in speeding up the development and refinement of effective materials for hydrogen storage, carbon capture, and gas separation. The exploration of the configurational adsorption space allows us to extract crucial information concerning, for example, the competition of water with CO2 for the adsorption binding sites. We find that only a few noble metals--Rh, Pd, Os, Ir, and Pt--favor the adsorption of CO2 and hence are potential candidates for effective carbon-capture materials. Our findings further reveal significant differences in the binding characteristics of H2, CO2, CH4, and H2O within the MOF structure, indicating that molecular blends can be successfully separated by these nano-porous materials. Supported by DOE DE-FG02-08ER46491.

Functionalized mesoporous silica materials for molsidomine adsorption: Thermodynamic study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alyoshina, Nonna A.; Parfenyuk, Elena V., E-mail: evp@iscras.ru

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 processmore » 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.« less

Cresyl Violet Adsorption on Sonicated Graphite Oxide.

PubMed

Coello-Fiallos, D; Cazzanelli, E; Tavolaro, A; Tavolaro, P; Arias, M; Caputi, L S

2018-04-01

We present a study of adsorption of Cresyl Violet (CV) in aqueous solution on sonicated Graphite Oxide (sGO). For comparison, we also show adsorption results of Methylene Blue (MB) and Acridine Orange (AO) performed in the same conditions. The adsorbent was synthesized by the Tour's method followed by washing in water and ethanol and sonication, without any reduction, and studied by Raman, IR, UV-Vis, SEM and TEM techniques. Our results show that adsorption fits the pseudosecond order model for the three dyes, and that the adsorption quantity for CV is 125.0 mg g-1, while for MB and AO is 123.3 and 94.6 mg g-1 respectively.

Adsorption and Retardation of PFASs in Soil

NASA Astrophysics Data System (ADS)

Chen, W.; Yan, N.; Fu, X.; Carroll, K. C.; Holguin, F. O. O.; Brusseau, M. L.

2017-12-01

Per- and poly-fluorinated alkyl substances (PFASs) are emerging contaminants of concern that are present in the subsurface at numerous military and industrial facilities. Knowledge of the retention behavior of these compounds in the subsurface environment is critical for effective risk characterization and remediation. The objective of this research is to investigate the role of adsorption at the air-water interface on PFAS retention in vadose-zone systems. Surface tensions were measured for select PFAS to determine interfacial adsorption coefficients. Column experiments were conducted to characterize retardation and transport under saturated and unsaturated flow conditions. The impact of soil properties and groundwater constituents on surface tension, solid-phase adsorption, and interfacial adsorption was investigated.

Defluoridation of drinking water using adsorption processes.

PubMed

Loganathan, Paripurnanda; Vigneswaran, Saravanamuthu; Kandasamy, Jaya; Naidu, Ravi

2013-03-15

Excessive intake of fluoride (F), mainly through drinking water, is a serious health hazard affecting humans worldwide. There are several methods used for the defluoridation of drinking water, of which adsorption processes are generally considered attractive because of their effectiveness, convenience, ease of operation, simplicity of design, and for economic and environmental reasons. In this paper, we present a comprehensive and a critical literature review on various adsorbents used for defluoridation, their relative effectiveness, mechanisms and thermodynamics of adsorption, and suggestions are made on choice of adsorbents for various circumstances. Effects of pH, temperature, kinetics and co-existing anions on F adsorption are also reviewed. Because the adsorption is very weak in extremely low or high pHs, depending on the adsorbent, acids or alkalis are used to desorb F and regenerate the adsorbents. However, adsorption capacity generally decreases with repeated use of the regenerated adsorbent. Future research needs to explore highly efficient, low cost adsorbents that can be easily regenerated for reuse over several cycles of operations without significant loss of adsorptive capacity and which have good hydraulic conductivity to prevent filter clogging during the fixed-bed treatment process. Copyright © 2013 Elsevier B.V. All rights reserved.

SeO2 adsorption on CaO surface: DFT and experimental study on the adsorption of multiple SeO2 molecules

NASA Astrophysics Data System (ADS)

Fan, Yaming; Zhuo, Yuqun; Li, Liangliang

2017-10-01

SeO2 adsorption mechanisms on CaO surface were firstly investigated by both density functional theory (DFT) calculations and adsorption experiments. Adsorption of multiple SeO2 on the CaO (001) surface was investigated using slab model. Based on the results of adsorption energy and surface property, a double-layer adsorption mechanisms were proposed. In experiments, the SeO2 adsorption products were prepared in a U-shaped quartz reactor at 200 °C. The surface morphology was investigated by field emission scanning electron microscopy (FE-SEM). The superficial and total SeO2 mass fractions were measured by X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma atomic emission spectroscopy (ICP-AES), respectively. The surface valence state and bulk structure are determined by XPS and X-Ray Diffraction (XRD). The experimental results are in good agreement with the DFT results. In conclusion, the fundamental SeO2 chemisorption mechanisms on CaO surface were suggested.

Adsorption mechanism of cadmium on juniper bark and wood

Treesearch

Eun Woo Shin; K. G. Karthikeyan; Mandla A. Tshabalala

2007-01-01

In this study the capacity of sorbents prepared from juniper wood (JW) and bark (JB) to adsorb cadmium (Cd) from aqueous solutions at different pH values was compared. Adsorption behavior was characterized through adsorption kinetics, adsorption isotherms, and adsorption edge experiments. Results from kinetics and isotherm experiments showed that JB (76.3–91.6 lmol Cd...

Adsorption and catalytic properties of sulfated aluminum oxide modified with cobalt ions

NASA Astrophysics Data System (ADS)

Lanin, S. N.; Bannykh, A. A.; Vlasenko, E. V.; Krotova, I. N.; Obrezkov, O. N.; Shilina, M. I.

2017-01-01

The adsorption properties of sulfated aluminum oxide (9% SO 4 2- /γ-Al2O3) and a cobalt-containing composite (0.5%Co/SO 4 2- /γ-Al2O3) based on it are studied via dynamic sorption. The adsorption isotherms of such test adsorbates as n-hydrocarbons (C6-C8), benzene, ethylbenzene, chloroform, and diethyl ether are measured, and their isosteric heats of adsorption are calculated. It is shown that the surface sulfation of aluminum oxide substantially improves its electron-accepting properties, and so the catalytic activity of SO 4 2- /γ-Al2O3 in the liquid-phase alkylation of benzene with octene-1 at temperatures of 25-120°C is one order of magnitude higher than for the initial aluminum oxide. It is established that additional modification of sulfated aluminum oxide with cobalt ions increases the activity of this catalyst by 2-4 times. It is shown that adsorption sites capable of strong specific adsorption with both donating (aromatics, diethyl ether chemosorption) and accepting molecules (chloroform) form on the surface of sulfated γ-Al2O3 promoted by cobalt salt.

Adsorption of lead over Graphite Oxide

PubMed Central

Olanipekun, Opeyemi; Oyefusi, Adebola; Neelgund, Gururaj M.; Oki, Aderemi

2014-01-01

The adsorption efficiency and kinetics of removal of lead in presence of graphite oxide (GO) was determined using the Atomic Absorption spectrophotometer (AAS). The GO was prepared by the chemical oxidation of graphite and characterized using FTIR, SEM, TGA and XRD. The adsorption efficiency of GO for the solution containing 50, 100 and 150 ppm of Pb2+ was found to be 98, 91 and 71% respectively. The adsorption ability of GO was found to be higher than graphite. Therefore, the oxidation of activated carbon in removal of heavy metals may be a viable option to reduce pollution in portable water. PMID:24152870

Arsenate adsorption mechanisms at the allophane - Water interface

USGS Publications Warehouse

Arai, Y.; Sparks, D.L.; Davis, J.A.

2005-01-01

We investigated arsenate (As(V)) reactivity and surface speciation on amorphous aluminosilicate mineral (synthetic allophane) surfaces using batch adsorption experiments, powder X-ray diffraction (XRD), and X-ray absorption spectroscopy (XAS). The adsorption isotherm experiments indicated that As(V) uptake increased with increasing [As(V)]0 from 50 to 1000 ??M (i.e., Langmuir type adsorption isotherm) and that the total As adsorption slightly decreased with increasing NaCl concentrations from 0.01 to 0.1 M. Arsenate adsorption was initially (0-10 h) rapid followed by a slow continuum uptake, and the adsorption processes reached the steady state after 720 h. X-ray absorption spectroscopic analyses suggest that As(V) predominantly forms bidentate binuclear surface species on aluminum octahedral structures, and these species are stable up to 11 months. Solubility calculations and powder XRD analyses indicate no evidence of crystalline AI-As(V) precipitates in the experimental systems. Overall, macroscopic and spectroscopic evidence suggest that the As(V) adsorption mechanisms at the allophane-water interface are attributable to ligand exchange reactions between As(V) and surface-coordinated water molecules and hydroxyl and silicate ions. The research findings imply that dissolved tetrahedral oxyanions (e.g., H2PO42- and H2AsO42-) are readily retained on amorphous aluminosilicate minerals in aquifer and soils at near neutral pH. The innersphere adsorption mechanisms might be important in controlling dissolved arsenate and phosphate in amorphous aluminosilicate-rich low-temperature geochemical environments. ?? 2005 American Chemical Society.

Adsorptive desulfurization with metal-organic frameworks: A density functional theory investigation

NASA Astrophysics Data System (ADS)

Chen, Zhiping; Ling, Lixia; Wang, Baojun; Fan, Huiling; Shangguan, Ju; Mi, Jie

2016-11-01

The contribution of each fragment of metal-organic frameworks (MOFs) to the adsorption of sulfur compounds were investigated using density functional theory (DFT). The involved sulfur compounds are dimethyl sulfide (CH3SCH3), ethyl mercaptan (CH3CH2SH) and hydrogen sulfide (H2S). MOFs with different organic ligands (NH2-BDC, BDC and NDC), metal centers structures (M, M-M and M3O) and metal ions (Zn, Cu and Fe) were used to study their effects on sulfur species adsorption. The results revealed that, MOFs with coordinatively unsaturated sites (CUS) have the strongest binding strength with sulfur compounds, MOFs with NH2-BDC substituent group ligand comes second, followed by that with saturated metal center, and the organic ligands without substituent group has the weakest adsorption strength. Moreover, it was also found that, among different metal ions (Fe, Zn and Cu), MOFs with unsaturated Fe has the strongest adsorption strength for sulfur compounds. These results are consistent with our previous experimental observations, and therefore provide insights on the better design of MOFs for desulfurization application.

Adsorption Property and Mechanism of Oxytetracycline onto Willow Residues

PubMed Central

Wang, Di; Xu, Haiyang; Yang, Shengke; Wang, Wenke; Wang, Yanhua

2017-01-01

To elucidate the adsorption property and the mechanism of plant residues to reduce oxytetracycline (OTC), the adsorption of OTC onto raw willow roots (WR-R), stems (WS-R), leaves (WL-R), and adsorption onto desugared willow roots (WR-D), stems (WS-D), and leaves (WL-D) were investigated. The structural characterization was analyzed by scanning electron microscopy, Fourier-transform infrared spectra, and an elemental analyzer. OTC adsorption onto the different tissues of willow residues was compared and correlated with their structures. The adsorption kinetics of OTC onto willow residues was found to follow the pseudo-first-order model. The isothermal adsorption process of OTC onto the different tissues of willow residues followed the Langmuir and Freundlich model and the process was also a spontaneous endothermic reaction, which was mainly physical adsorption. After the willow residues were desugared, the polarity decreased and the aromaticity increased, which explained why the adsorption amounts of the desugared willow residues were higher than those of the unmodified residues. These observations suggest that the raw and modified willow residues have great potential as adsorbents to remove organic pollutants. PMID:29271892

Adsorption and excess fission Xe - Adsorption of Xe on vacuum crushed minerals

NASA Technical Reports Server (NTRS)

Bernatowicz, T. J.; Kramer, F. E.; Podosek, F. A.; Honda, M.

1982-01-01

It is hypothesized that adsorption is not likely to provide a sufficiently precise mechanism for the concentration of excess fission Xe in the entire lunar regolith, in view of laboratory analogs of the lunar soil and calculations of the residence times of noble gases in the present day regolith. Lunar cold trap and episodic degassing models are difficult to reconcile, however, with the generality of excess fission Xe in all gas-rich highland breccias. It is concluded that the high Xe concentration in such highland breccias is not the result of Xe adsorption prior to the trapping of this component.

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. Copyright © 2015 Elsevier Inc. All rights reserved.

Gas adsorption properties of hybrid graphene-MOF materials.

PubMed

Szczęśniak, Barbara; Choma, Jerzy; Jaroniec, Mietek

2018-03-15

Nowadays, hybrid porous materials consisting of metal-organic frameworks (MOFs) and graphene nanosheets become more and more attractive because of their growing applications in adsorption, catalysis and related areas. Incorporation of graphene oxide into MOFs can provide benefits such as increased water resistance and thermal stability as well as enhanced surface area and adsorption properties. Graphene oxide is one of the best additives to other materials owing to its two main virtues: high atomic density and large amount of surface functional groups. Due to its dense array of atoms, graphene oxide can significantly increase dispersion forces in graphene-MOF materials, which is beneficial for adsorption of small molecules. This work presents a concise appraisal of adsorption properties of MOFs and graphene-MOF hybrids toward CO 2 , volatile organic compounds, hydrogen and methane. It shows that the graphene-MOF materials represent an important class of materials with potential applications in adsorption and catalysis. A special emphasis of this article is placed on their adsorption applications for gas capture and storage. A large number of graphene-MOF adsorbents has been so far explored and their appraisal could be beneficial for researchers interested in the development of hybrid adsorbents for adsorption-based applications. Copyright © 2017 Elsevier Inc. All rights reserved.

Water-quality characteristics, including sodium-adsorption ratios, for four sites in the Powder River drainage basin, Wyoming and Montana, water years 2001-2004

USGS Publications Warehouse

Clark, Melanie L.; Mason, Jon P.

2006-01-01

The U.S. Geological Survey, in cooperation with the Wyoming Department of Environmental Quality, monitors streams throughout the Powder River structural basin in Wyoming and parts of Montana for potential effects of coalbed natural gas development. Specific conductance and sodium-adsorption ratios may be larger in coalbed waters than in stream waters that may receive the discharge waters. Therefore, continuous water-quality instruments for specific conductance were installed and discrete water-quality samples were collected to characterize water quality during water years 2001-2004 at four sites in the Powder River drainage basin: Powder River at Sussex, Wyoming; Crazy Woman Creek near Arvada, Wyoming; Clear Creek near Arvada, Wyoming; and Powder River at Moorhead, Montana. During water years 2001-2004, the median specific conductance of 2,270 microsiemens per centimeter at 25 degrees Celsius (?S/cm) in discrete samples from the Powder River at Sussex, Wyoming, was larger than the median specific conductance of 1,930 ?S/cm in discrete samples collected downstream from the Powder River at Moorhead, Montana. The median specific conductance was smallest in discrete samples from Clear Creek (1,180 ?S/cm), which has a dilution effect on the specific conductance for the Powder River at Moorhead, Montana. The daily mean specific conductance from continuous water-quality instruments during the irrigation season showed the same spatial pattern as specific conductance values for the discrete samples. Dissolved sodium, sodium-adsorption ratios, and dissolved solids generally showed the same spatial pattern as specific conductance. The largest median sodium concentration (274 milligrams per liter) and the largest range of sodium-adsorption ratios (3.7 to 21) were measured in discrete samples from the Powder River at Sussex, Wyoming. Median concentrations of sodium and sodium-adsorption ratios were substantially smaller in Crazy Woman Creek and Clear Creek, which tend to

Regenerating an Arsenic Removal Iron-Based Adsorptive ...

EPA Pesticide Factsheets

The replacement of exhausted, adsorptive media used to remove arsenic from drinking water accounts for approximately 80% of the total operational and maintenance (O/M) costs of this commonly used small system technology. The results of three, full scale system studies of an on-site media regeneration process (Part 1) showed it to be effective in stripping arsenic and other contaminants from the exhausted media. Part 2, of this two part paper, presents information on the performance of the regenerated media to remove arsenic through multiple regeneration cycles (3) and the approximate cost savings of regeneration over media replacement. The results of the studies indicate that regenerated media is very effective in removing arsenic and the regeneration cost is substantially less than the media replacement cost. On site regeneration, therefore, provides small systems with alternative to media replacement when removing arsenic from drinking water using adsorptive media technology. Part 2 of a two part paper on the performance of the regenerated media to remove arsenic through multiple regeneration cycles (3) and the approximate cost savings of regeneration over media replacement.

Effect of soil pH and organic matter on the adsorption and desorption of pentachlorophenol.

PubMed

Chien, Shui-Wen Chang; Chen, Shou-Hung; Li, Chi-Jui

2018-02-01

Various properties of soil affect the partition of organic contaminants within, and conversely, the properties of the organic contaminants also directly affect their partition behavior in soil. Therefore, understanding the effects of various properties of soil on the partition of organic contaminants favors subsequent assessment and provides soil remediation methods for policymakers. This study selected pentachlorophenol (PCP), a common hydrophobic ionizable organic compound in contaminated sites worldwide, as the target contaminant. The effects of pH, organic matter, and the combination of both, on PCP adsorption/desorption behavior in soil were investigated. Phosphoric acid and potassium hydroxide were used as buffer solutions to modify the soil pH by the batch and column extraction methods. A common retail organic fertilizer and fulvic acid were selected as additives to manipulate the soil organic content. Modifying the pH of the soil samples revealed that acidic soil exhibited a greater PCP adsorption rate than alkaline soil. The amount of PCP desorption increased regardless of pH of the in situ contaminated soil. The adsorption of PCP increased with increasing amount of organic additive. However, addition of fulvic acid yielded different results compared to the addition of organic fertilizer. Specifically, the organic fertilizer could not compete with the in situ contaminated soil in PCP adsorption, whereas fulvic acids increased the PCP dissolution to facilitate adsorbing contaminant adsorption. The combined effect of pH modification and organic matter addition provides additional PCP adsorption sites; therefore, adding the organic fertilizer to decrease the soil pH elevated the PCP adsorption rates of the laterite, alluvial, and in situ contaminated soil samples. The study results revealed that both pH and organic matter content are crucial to PCP adsorption/desorption in soil. Therefore, the effects of soil pH and organic matter should be considered in

High capacity adsorption media and method of producing

DOEpatents

Tranter, Troy J.; Mann, Nicholas R.; Todd, Terry A.; Herbst, Ronald S.

2010-10-05

A method of producing an adsorption medium to remove at least one constituent from a feed stream. The method comprises dissolving and/or suspending at least one metal compound in a solvent to form a metal solution, dissolving polyacrylonitrile into the metal solution to form a PAN-metal solution, and depositing the PAN-metal solution into a quenching bath to produce the adsorption medium. The at least one constituent, such as arsenic, selenium, or antimony, is removed from the feed stream by passing the feed stream through the adsorption medium. An adsorption medium having an increased metal loading and increased capacity for arresting the at least one constituent to be removed is also disclosed. The adsorption medium includes a polyacrylonitrile matrix and at least one metal hydroxide incorporated into the polyacrylonitrile matrix.

High capacity adsorption media and method of producing

DOEpatents

Tranter, Troy J [Idaho Falls, ID; Herbst, R Scott [Idaho Falls, ID; Mann, Nicholas R [Blackfoot, ID; Todd, Terry A [Aberdeen, ID

2008-05-06

A method of producing an adsorption medium to remove at least one constituent from a feed stream. The method comprises dissolving at least one metal compound in a solvent to form a metal solution, dissolving polyacrylonitrile into the metal solution to form a PAN-metal solution, and depositing the PAN-metal solution into a quenching bath to produce the adsorption medium. The at least one constituent, such as arsenic, selenium, or antimony, is removed from the feed stream by passing the feed stream through the adsorption medium. An adsorption medium having an increased metal loading and increased capacity for arresting the at least one constituent to be removed is also disclosed. The adsorption medium includes a polyacrylonitrile matrix and at least one metal hydroxide incorporated into the polyacrylonitrile matrix.

Adsorption of surfactants and polymers at interfaces

NASA Astrophysics Data System (ADS)

Rojas, Orlando Jose

Surface tension and high-resolution laser light scattering experiments were used to investigate the adsorption of isomeric sugar-based surfactants at the air/liquid interface in terms of surfactant surface packing and rheology. Soluble monolayers of submicellar surfactant solutions exhibited a relatively viscous behavior. It was also proved that light scattering of high-frequency thermally-induced capillary waves can be utilized to study surfactant exchange between the surface and the bulk solution. Such analysis revealed the existence of a diffusional relaxation mechanism. A procedure based on XPS was developed for quantification, on an absolute basis, of polymer adsorption on mica and Langmuir-Blodgett cellulose films. The adsorption of cationic polyelectrolytes on negatively-charged solid surfaces was highly dependent on the polymer ionicity. It was found that the adsorption process is driven by electrostatic mechanisms. Charge overcompensation (or charge reversal) of mica occurred after adsorption of polyelectrolytes of ca. 50% charge density, or higher. It was demonstrated that low-charge-density polyelectrolytes adsorb on solid surfaces with an extended configuration dominated by loops and tails. In this case the extent of adsorption is limited by steric constraints. The conformation of the polyelectrolyte in the adsorbed layer is dramatically affected by the presence of salts or surfactants in aqueous solution. The phenomena which occur upon increasing the ionic strength are consistent with the screening of the electrostatic attraction between polyelectrolyte segments and solid surface. This situation leads to polyelectrolyte desorption accompanied by both an increase in the layer thickness and the range of the steric force. Adsorbed polyelectrolytes and oppositely charged surfactants readily associate at the solid/liquid interface. Such association induces polyelectrolyte desorption at a surfactant concentration which depends on the polyelectrolyte charge

The adsorption properties of CHx species on metal modified graphene

NASA Astrophysics Data System (ADS)

Tang, Yanan; Shen, Zigang; Chen, Weiguang; Zhu, Dalei; Chai, Huadou; Zhao, Mingyu

2018-05-01

The adsorption geometries of CHx species (x = 0, 1, 2, 3 and 4) on the metal embedded graphene (M-graphene) substrates and the change in electronic structure and magnetic property of systems are analyzed using the first-principles calculations. The calculated results show that the doped metal atoms can provide transferred electrons to neighboring carbon atoms at defective site and thus exhibit positive charges, as well as turning the adsorption sensing of M-graphene for detecting CHx species. Compared with the adsorbed CH3, the adsorption of C, CH and CH2 species exhibit more stability ( >3.0 eV) on M-graphene. Besides, more stable C atom on M-graphene can effectively turn the magnetic property of systems as compared with other species. This result provides a useful reference for fabricating the functional metal-graphene complex as gas sensors and catalytic materials.

Adsorption-desorption of oxytetracycline on marine sediments: Kinetics and influencing factors.

PubMed

Li, Jia; Zhang, Hua

2016-12-01

To reveal the kinetics and mechanisms of antibiotic adsorption/desorption processes, batch and stirred flow chamber (SFC) experiments were carried out with oxytetracycline (OTC) on two marine sediments. The OTC adsorption capacities of the marine sediments were relatively weak and related to their organic carbon (OC) and contents of fine particles. Sorption isotherms of OTC on marine sediment can be well described by both the Langmuir and Freundlich models. Langmuir adsorption maxima (q max ) and Freundlich distribution coefficients (K f ) increased with the decrease of salinity and pH, which indicated the importance of variable charged sites on sediment surfaces. A second order kinetic model successfully described adsorption and desorption kinetics of OTC and well reproduced the concentration change during stop-flow. The adsorption kinetic rates (k a ) for OTC under different experimental conditions ranged from 2.00 × 10 -4 to 1.97 × 10 -3  L (mg min) -1 . Results of SFC experiments indicated that diffusive mass transfer was the dominant mechanism of the time-dependent adsorption of OTC and its release from marine sediment was mildly hysteretic. The high desorption percentage (43-75% for LZB and 58-75% for BHB) implied that binding strength of OTC on two marine sediments was weak. In conclusion, marine sediment characteristics and environmental factors such as salinity, pH, and flow rate are critical factors determine extent of OTC sorption on marine sediment and need to be incorporated in modeling fate and transport of OTC in marine environment. Copyright © 2016 Elsevier Ltd. All rights reserved.

Predicting heavy metals' adsorption edges and adsorption isotherms on MnO2 with the parameters determined from Langmuir kinetics.

PubMed

Hu, Qinghai; Xiao, Zhongjin; Xiong, Xinmei; Zhou, Gongming; Guan, Xiaohong

2015-01-01

Although surface complexation models have been widely used to describe the adsorption of heavy metals, few studies have verified the feasibility of modeling the adsorption kinetics, edge, and isotherm data with one pH-independent parameter. A close inspection of the derivation process of Langmuir isotherm revealed that the equilibrium constant derived from the Langmuir kinetic model, KS-kinetic, is theoretically equivalent to the adsorption constant in Langmuir isotherm, KS-Langmuir. The modified Langmuir kinetic model (MLK model) and modified Langmuir isotherm model (MLI model) incorporating pH factor were developed. The MLK model was employed to simulate the adsorption kinetics of Cu(II), Co(II), Cd(II), Zn(II) and Ni(II) on MnO2 at pH3.2 or 3.3 to get the values of KS-kinetic. The adsorption edges of heavy metals could be modeled with the modified metal partitioning model (MMP model), and the values of KS-Langmuir were obtained. The values of KS-kinetic and KS-Langmuir are very close to each other, validating that the constants obtained by these two methods are basically the same. The MMP model with KS-kinetic constants could predict the adsorption edges of heavy metals on MnO2 very well at different adsorbent/adsorbate concentrations. Moreover, the adsorption isotherms of heavy metals on MnO2 at various pH levels could be predicted reasonably well by the MLI model with the KS-kinetic constants. Copyright © 2014. Published by Elsevier B.V.

Adsorption of emerging contaminant metformin using graphene oxide.

PubMed

Zhu, Shuai; Liu, Yun-Guo; Liu, Shao-Bo; Zeng, Guang-Ming; Jiang, Lu-Hua; Tan, Xiao-Fei; Zhou, Lu; Zeng, Wei; Li, Ting-Ting; Yang, Chun-Ping

2017-07-01

The occurrence of emerging contaminants in our water resources poses potential threats to the livings. Due to the poor treatment in wastewater management, treatment technologies are needed to effectively remove these products for living organism safety. In this study, Graphene oxide (GO) was tested for the first time for its capacity to remove a kind of emerging wastewater contaminants, metformin. The research was conducted by using a series of systematic adsorption and kinetic experiments. The results indicated that GO could rapidly and efficiently reduce the concentration of metformin, which could provide a solution in handling this problem. The uptake of metformin on the graphene oxide was strongly dependent on temperature, pH, ionic strength, and background electrolyte. The adsorption kinetic experiments revealed that almost 80% removal of metformin was achieved within 20 min for all the doses studied, corresponding to the relatively high k 1 (0.232 min -1 ) and k 2 (0.007 g mg -1  min -1 ) values in the kinetic models. It indicated that the highest adsorption capacity in the investigated range (q m ) of GO for metformin was at pH 6.0 and 288 K. Thermodynamic study indicated that the adsorption was a spontaneous (ΔG 0  < 0) and exothermic (ΔH 0  < 0) process. The adsorption of metformin increased when the pH values changed from 4.0 to 6.0, and decreased adsorption were observed at pH 6.0-11.0. GO still exhibited excellent adsorption capacity after several desorption/adsorption cycles. Besides, both so-called π-π interactions and hydrogen bonds might be mainly responsible for the adsorption of metformin onto GO. Copyright © 2017 Elsevier Ltd. All rights reserved.

Chlorate adsorption from chlor-alkali plant brine stream.

PubMed

Lakshmanan, Shyam; Murugesan, Thanabalan

2017-07-01

Chlorates are present in the brine stream purged from chlor-alkali plants. Tests were conducted using activated carbon from coconut shell, coal or palm kernel shell to adsorb chlorate. The results show varying levels of adsorption with reduction ranging between 1.3 g/L and 1.8 g/L. This was higher than the chlorate generation rate of that plant, recorded at 1.22 g/L, indicating that chlorate can be adequately removed by adsorption using activated carbon. Coconut based activated carbon exhibited the best adsorption of chlorate of the three types of activated carbon tested. Introducing an adsorption step prior to purging of the brine will be able to reduce chlorate content in the brine stream. The best location for introducing the adsorption step was identified to be after dechlorination of the brine and before resaturation. Introduction of such an adsorption step will enable complete recovery of the brine and prevent brine purging, which in turn will result in less release of chlorides and chlorates to the environment.

Albumin adsorption on CoCrMo alloy surfaces

NASA Astrophysics Data System (ADS)

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

2015-12-01

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

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

DOE PAGES

Joan E. Thomas; Kelley, Michael J.

2009-10-20

In this study, analysis of DRIFTS spectra was used for a quantitative study of competitive adsorption of myristic and salicylic acids onto kaolinite or γ-alumina. Peaks unique to the ring or the chain were selected and single molecule studies used as calibration. Samples were exposed to hexane solution containing equal molecular quantities of each acid. The surface loading of salicylic acid was not influenced by the presence of myristic acid on either mineral but the maximum loading of myristic acid was decreased (46-50%) by salicylic acid. Displacement of myristic acid from {gamma}-alumina, but not kaolinite, was observed when excess salicylicmore » acid remained in solution. A 25% increase in the maximum loading was observed for kaolinite, but not for{gamma}-alumina. On {gamma}-alumina, after a loading of 1 molecule per nm 2, 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

Adsorption and co-adsorption of graphene oxide and Ni(II) on iron oxides: A spectroscopic and microscopic investigation.

PubMed

Sheng, Guodong; Huang, Chengcai; Chen, Guohe; Sheng, Jiang; Ren, Xuemei; Hu, Baowei; Ma, Jingyuan; Wang, Xiangke; Huang, Yuying; Alsaedi, Ahmed; Hayat, Tasawar

2018-02-01

Graphene oxide (GO) may strongly interact with toxic metal ions and mineral particles upon release into the soil environment. We evaluated the mutual effects between GO and Ni (Ni(II)) with regard to their adsorption and co-adsorption on two minerals (goethite and hematite) in aqueous phase. Results indicated that GO and Ni could mutually facilitate the adsorption of each other on both goethite and hematite over a wide pH range. Addition of Ni promoted GO co-adsorption mainly due to the increased positive charge of minerals and cation-π interactions, while the presence of GO enhanced Ni co-adsorption predominantly due to neutralization of positive charge and strong interaction with oxygen-containing functional groups on adsorbed GO. Increasing adsorption of GO and Ni on minerals as they coexist may thus reduce their mobility in soil. Extended X-ray absorption fine structure (EXAFS) spectroscopy data revealed that GO altered the microstructure of Ni on minerals, i.e., Ni formed edge-sharing surface species (at R Ni-Fe ∼3.2 Å) without GO, while a GO-bridging ternary surface complexes (at R Ni-C ∼2.49 Å and R Ni-Fe ∼4.23 Å) was formed with GO. These findings improved the understanding of potential fate and toxicity of GO as well as the partitioning processes of Ni ions in aquatic and soil environments. Copyright © 2017 Elsevier Ltd. All rights reserved.

An adsorption of carbon dioxide on activated carbon controlled by temperature swing adsorption

NASA Astrophysics Data System (ADS)

Tomas, Korinek; Karel, Frana

2017-09-01

This work deals with a method of capturing carbon dioxide (CO2) in indoor air. Temperature Swing Adsorption (TSA) on solid adsorbent was chosen for CO2 capture. Commercial activated carbon (AC) in form of extruded pellets was used as a solid adsorbent. There was constructed a simple device to testing effectiveness of CO2 capture in a fixed bed with AC. The TSA cycle was also simulated using the open-source software OpenFOAM. There was a good agreement between results obtained from numerical simulations and experimental data for adsorption process.

Adsorption of heavy metals by road deposited solids.

PubMed

Gunawardana, Chandima; Goonetilleke, Ashantha; Egodawatta, Prasanna

2013-01-01

The research study discussed in the paper investigated the adsorption/desorption behaviour of heavy metals commonly deposited on urban road surfaces, namely, Zn, Cu, Cr and Pb, for different particle size ranges of solids. The study outcomes, based on field studies and batch experiments, confirmed that road deposited solids particles contain a significantly high amount of vacant charge sites with the potential to adsorb additional heavy metals. Kinetic studies and adsorption experiments indicated that Cr is the most preferred metal element to associate with solids due to the relatively high electronegativity and high charge density of trivalent cation (Cr(3+)). However, the relatively low availability of Cr in the urban road environment could influence this behaviour. Comparing total adsorbed metals present in solids particles, it was found that Zn has the highest capacity for adsorption to solids. Desorption experiments confirmed that a low concentration of Cu, Cr and Pb in solids was present in water-soluble and exchangeable form, whilst a significant fraction of adsorbed Zn has a high likelihood of being released back into solution. Among heavy metals, Zn is considered to be the most commonly available metal among road surface pollutants.

Adsorption of arsenic from aqueous solution using magnetic graphene oxide

NASA Astrophysics Data System (ADS)

Sherlala, A. I. A.; Raman, A. A.; Bello, M. M.

2017-06-01

A binary of graphene oxide (GO) and iron oxide (IO) was prepared and used for the removal of arsenic from aqueous solution. The synthesized compound was characterized using XRD analysis. The prepared composite was used for the adsorption of arsenic from aqueous solution. Central Composite Design was used to design the adsorption experiments and to investigate the effects of operational parameters (initial concentration of arsenic, adsorbent dosage, pH and time) on the adsorption capacity and efficiency. The adsorbent shows a high adsorption capacity for the arsenic. The adsorption efficiency ranges between 33.2 % and 99.95 %. The most significant factors affecting the adsorption capacity were found to be the initial concentration of arsenic and the adsorbent dosage. The initial pH of the solution slightly affects the adsorption capacity, with the maximum adsorption capacity occurring around pH 6 - 7. Thus, the developed adsorbent has a potential for effective removal of arsenic from aqueous solution.

Highly Enhanced Gas Adsorption Properties in Vertically Aligned MoS2 Layers.

PubMed

Cho, Soo-Yeon; Kim, Seon Joon; Lee, Youhan; Kim, Jong-Seon; Jung, Woo-Bin; Yoo, Hae-Wook; Kim, Jihan; Jung, Hee-Tae

2015-09-22

In this work, we demonstrate that gas adsorption is significantly higher in edge sites of vertically aligned MoS2 compared to that of the conventional basal plane exposed MoS2 films. To compare the effect of the alignment of MoS2 on the gas adsorption properties, we synthesized three distinct MoS2 films with different alignment directions ((1) horizontally aligned MoS2 (basal plane exposed), (2) mixture of horizontally aligned MoS2 and vertically aligned layers (basal and edge exposed), and (3) vertically aligned MoS2 (edge exposed)) by using rapid sulfurization method of CVD process. Vertically aligned MoS2 film shows about 5-fold enhanced sensitivity to NO2 gas molecules compared to horizontally aligned MoS2 film. Vertically aligned MoS2 has superior resistance variation compared to horizontally aligned MoS2 even with same surface area exposed to identical concentration of gas molecules. We found that electrical response to target gas molecules correlates directly with the density of the exposed edge sites of MoS2 due to high adsorption of gas molecules onto edge sites of vertically aligned MoS2. Density functional theory (DFT) calculations corroborate the experimental results as stronger NO2 binding energies are computed for multiple configurations near the edge sites of MoS2, which verifies that electrical response to target gas molecules (NO2) correlates directly with the density of the exposed edge sites of MoS2 due to high adsorption of gas molecules onto edge sites of vertically aligned MoS2. We believe that this observation extends to other 2D TMD materials as well as MoS2 and can be applied to significantly enhance the gas sensor performance in these materials.

Molecular simulation of CH4/CO2/H2O competitive adsorption on low rank coal vitrinite.

PubMed

Yu, Song; Bo, Jiang; Wu, Li

2017-07-21

The competitive adsorptions of CH 4 /CO 2 /H 2 O on coal vitrinite (DV-8, C 214 H 180 O 24 N 2 ) were computed based on density function theory (DFT) and grand canonical Monte Carlo (GCMC). The adsorption process reaches the saturation state after adsorbing 17 CH 4 s, 22 CO 2 s, and 35 H 2 Os per C 214 H 180 O 24 N 2 respectively. The optimal configurations of CH 4 -vitrinite, CO 2 -vitrinite, and H 2 O-vitrinite respectively manifest as aromatic 1 /T 2 /rT 3 (1 adsorption location, 2 adsorption sites and T here represents sites above the carbon atom and the heteroatom, 3 adsorption orientation and rT here means the orientations of three hydrogen atoms pointing to vitrinite), aromatic/T/v (v represents the orientations perpendicular to the plane of vitrinite), and aromatic/rV/T (rV represents an oxygen atom pointing to the vitrinite surface). The GCMC results show that high temperature is not conducive to the vitrinite's adsorption of adsorbates and the adsorption capacity order is H 2 O > CO 2 > CH 4 (263-363 K) in the one-component, binary, and ternary adsorbate systems. The optimal configurations of vitrinite are similar to graphite/graphene, while ΔE is significantly lower than graphite/graphene. Simulation data are in good agreement with the experimental results.

Experimental and theoretical study using DFT method for the competitive adsorption of two cationic dyes from wastewaters

NASA Astrophysics Data System (ADS)

Regti, Abdelmajid; Ayouchia, Hicham Ben El; Laamari, My Rachid; Stiriba, Salah Eddine; Anane, Hafid; Haddad, Mohammadine El

2016-12-01

The adsorption of cationic dyes, Basic Yellow (BY28) and Methylene Blue (MB) on a new activated carbon from medlar species were studied in both single and binary system. Some experimental parameters, namely, pH, amount of adsorbent and contact time are studied. Quantum chemical results indicate that the adsorption efficiency was directly related to the dye electrophilicity power. Some theorical parameters were calculated and proved that MB is more electrophilic than BY28, than greatest interaction with surface sites. Kinetic study showed that the adsorption follows the pseudo-second-order model and Freundlich was the best model to describe the phenomenon in the single and binary system. According to the local reactivity results using Parr functions, the sulphur and nitrogen atoms will be the main adsorption sites.

[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

Adsorption of lead over graphite oxide.

PubMed

Olanipekun, Opeyemi; Oyefusi, Adebola; Neelgund, Gururaj M; Oki, Aderemi

2014-01-24

The adsorption efficiency and kinetics of removal of lead in presence of graphite oxide (GO) was determined using the Atomic Absorption Spectrophotometer (AAS). The GO was prepared by the chemical oxidation of graphite and characterized using FTIR, SEM, TGA and XRD. The adsorption efficiency of GO for the solution containing 50, 100 and 150 ppm of Pb(2+) was found to be 98%, 91% and 71% respectively. The adsorption ability of GO was found to be higher than graphite. Therefore, the oxidation of activated carbon in removal of heavy metals may be a viable option to reduce pollution in portable water. Published by Elsevier B.V.

Dissociative adsorption of a multifunctional compound on a semiconductor surface: a theoretical study of the adsorption of hydroxylamine on Ge(100).

PubMed

Park, Hyunkyung; Kim, Do Hwan

2018-06-06

The adsorption behavior of hydroxylamine on a Ge(100) surface was investigated using density functional theory (DFT) calculations. These calculations predicted that hydroxylamine, a multifunctional compound consisting of a hydroxyl group and an amine group, would initially become adsorbed through N-dative bonding, or alternatively through the hydroxyl group via O-H dissociative adsorption. An N-O dissociative reaction may also occur, mainly via N-dative molecular adsorption, and the N-O dissociative product was calculated to be the most stable of all the possible adsorption structures. The calculations furthermore indicated the formation of the N-O dissociative product from the N-dative structure to be nearly barrierless and the dissociated hydroxyl and amine groups to be bonded to two Ge atoms of adjacent Ge dimers. Simulated STM images suggested the change in electron density that would occur upon adsorption of hydroxylamine in various adsorption configurations, and specifically indicated the N-O dissociative product to have greater electron density around the amine groups, and the hydroxyl groups to mainly contribute electron density to the unoccupied electronic states.

Selective adsorption of flavor-active components on hydrophobic resins.

PubMed

Saffarionpour, Shima; Sevillano, David Mendez; Van der Wielen, Luuk A M; Noordman, T Reinoud; Brouwer, Eric; Ottens, Marcel

2016-12-09

This work aims to propose an optimum resin that can be used in industrial adsorption process for tuning flavor-active components or removal of ethanol for producing an alcohol-free beer. A procedure is reported for selective adsorption of volatile aroma components from water/ethanol mixtures on synthetic hydrophobic resins. High throughput 96-well microtiter-plates batch uptake experimentation is applied for screening resins for adsorption of esters (i.e. isoamyl acetate, and ethyl acetate), higher alcohols (i.e. isoamyl alcohol and isobutyl alcohol), a diketone (diacetyl) and ethanol. The miniaturized batch uptake method is adapted for adsorption of volatile components, and validated with column breakthrough analysis. The results of single-component adsorption tests on Sepabeads SP20-SS are expressed in single-component Langmuir, Freundlich, and Sips isotherm models and multi-component versions of Langmuir and Sips models are applied for expressing multi-component adsorption results obtained on several tested resins. The adsorption parameters are regressed and the selectivity over ethanol is calculated for each tested component and tested resin. Resin scores for four different scenarios of selective adsorption of esters, higher alcohols, diacetyl, and ethanol are obtained. The optimal resin for adsorption of esters is Sepabeads SP20-SS with resin score of 87% and for selective removal of higher alcohols, XAD16N, and XAD4 from Amberlite resin series are proposed with scores of 80 and 74% respectively. For adsorption of diacetyl, XAD16N and XAD4 resins with score of 86% are the optimum choice and Sepabeads SP2MGS and XAD761 resins showed the highest affinity towards ethanol. Copyright © 2016 Elsevier B.V. All rights reserved.

Adsorption and dissociation of molecular hydrogen on the (0001) surface of double hexagonal close packed americium

NASA Astrophysics Data System (ADS)

Dholabhai, P. P.; Ray, A. K.

2009-01-01

Hydrogen molecule adsorption on the (0001) surface of double hexagonal packed americium has been studied in detail within the framework of density functional theory using a full-potential all-electron linearized augmented plane wave plus local orbitals method (FP-L/APW+lo). Weak molecular hydrogen adsorptions were observed. Adsorption energies were optimized with respect to the distance of the adsorbates from the surface for three approach positions at three adsorption sites, namely t1 (one-fold top), b2 (two-fold bridge), and h3 (three-fold hollow) sites. Adsorption energies were computed at the scalar-relativistic level (no spin-orbit coupling NSOC) and at the fully relativistic level (with spin-orbit coupling SOC). The most stable configuration corresponds to a horizontal adsorption with the molecular approach being perpendicular to a lattice vector. The surface coverage is equivalent to one-fourth of a monolayer (ML), with the adsorption energies at the NSOC and SOC theoretical levels being 0.0997 eV and 0.1022 eV, respectively. The respective distance of the hydrogen molecule from the surface and hydrogen-hydrogen distance was found to be 2.645 Å and 0.789 Å, respectively. The work functions decreased and the net magnetic moments remained almost unchanged in all cases compared with the corresponding quantities of bare dhcp Am (0001) surface. The adsorbate-substrate interactions have been analyzed in detail using the partial charges inside the muffin-tin spheres, difference charge density distributions, and the local density of states. The effects of adsorption on the Am 5f electron localization-delocalization characteristics have been discussed. Reaction barrier for the dissociation of hydrogen molecule has been presented.

Adsorption coefficients for TNT on soil and clay minerals

NASA Astrophysics Data System (ADS)

Rivera, Rosángela; Pabón, Julissa; Pérez, Omarie; Muñoz, Miguel A.; Mina, Nairmen

2007-04-01

To understand the fate and transport mechanisms of TNT from buried landmines is it essential to determine the adsorption process of TNT on soil and clay minerals. In this research, soil samples from horizons Ap and A from Jobos Series at Isabela, Puerto Rico were studied. The clay fractions were separated from the other soil components by centrifugation. Using the hydrometer method the particle size distribution for the soil horizons was obtained. Physical and chemical characterization studies such as cation exchange capacity (CEC), surface area, percent of organic matter and pH were performed for the soil and clay samples. A complete mineralogical characterization of clay fractions using X-ray diffraction analysis reveals the presence of kaolinite, goethite, hematite, gibbsite and quartz. In order to obtain adsorption coefficients (K d values) for the TNT-soil and TNT-clay interactions high performance liquid chromatography (HPLC) was used. The adsorption process for TNT-soil was described by the Langmuir model. A higher adsorption was observed in the Ap horizon. The Freundlich model described the adsorption process for TNT-clay interactions. The affinity and relative adsorption capacity of the clay for TNT were higher in the A horizon. These results suggest that adsorption by soil organic matter predominates over adsorption on clay minerals when significant soil organic matter content is present. It was found that, properties like cation exchange capacity and surface area are important factors in the adsorption of clayey soils.

Toward Accurate Adsorption Energetics on Clay Surfaces

PubMed Central

2016-01-01

Clay minerals are ubiquitous in nature, and the manner in which they interact with their surroundings has important industrial and environmental implications. Consequently, a molecular-level understanding of the adsorption of molecules on clay surfaces is crucial. In this regard computer simulations play an important role, yet the accuracy of widely used empirical force fields (FF) and density functional theory (DFT) exchange-correlation functionals is often unclear in adsorption systems dominated by weak interactions. Herein we present results from quantum Monte Carlo (QMC) for water and methanol adsorption on the prototypical clay kaolinite. To the best of our knowledge, this is the first time QMC has been used to investigate adsorption at a complex, natural surface such as a clay. As well as being valuable in their own right, the QMC benchmarks obtained provide reference data against which the performance of cheaper DFT methods can be tested. Indeed using various DFT exchange-correlation functionals yields a very broad range of adsorption energies, and it is unclear a priori which evaluation is better. QMC reveals that in the systems considered here it is essential to account for van der Waals (vdW) dispersion forces since this alters both the absolute and relative adsorption energies of water and methanol. We show, via FF simulations, that incorrect relative energies can lead to significant changes in the interfacial densities of water and methanol solutions at the kaolinite interface. Despite the clear improvements offered by the vdW-corrected and the vdW-inclusive functionals, absolute adsorption energies are often overestimated, suggesting that the treatment of vdW forces in DFT is not yet a solved problem. PMID:27917256

Poliovirus adsorption by 34 minerals and soils.

PubMed

Moore, R S; Taylor, D H; Sturman, L S; Reddy, M M; Fuhs, G W

1981-12-01

The adsorption of radiolabeled infectious poliovirus type 2 by 34 well-defined soils and mineral substrates was analyzed in a synthetic freshwater medium containing 1 mM CaCl(2) and 1.25 mM NaHCO(3) at pH 7. In a model system, adsorption of poliovirus by Ottawa sand was rapid and reached equilibrium within 1 h at 4 degrees C. Near saturation, the adsorption could be described by the Langmuir equation; the apparent surface saturation was 2.5 x 10(6) plaque-forming units of poliovirus per mg of Ottawa sand. At low surface coverage, adsorption was described by the Freundlich equation. The soils and minerals used ranged from acidic to basic and from high in organic content to organic free. The available negative surface charge on each substrate was measured by the adsorption of a cationic polyelectrolyte, polydiallyldimethylammonium chloride. Most of the substrates adsorbed more than 95% of the virus. In general, soils, in comparison with minerals, were weak adsorbents. Among the soils, muck and Genesee silt loam were the poorest adsorbents; among the minerals, montmorillonite, glauconite, and bituminous shale were the least effective. The most effective adsorbents were magnetite sand and hematite, which are predominantly oxides of iron. Correlation coefficients for substrate properties and virus adsorption revealed that the elemental composition of the adsorbents had little effect on poliovirus uptake. Substrate surface area and pH, by themselves, were not significantly correlated with poliovirus uptake. A strong negative correlation was found between poliovirus adsorption and both the contents of organic matter and the available negative surface charge on the substrates as determined by their capacities for adsorbing the cationic polyelectrolyte, polydiallyldimethylammonium chloride.

[Adsorption of Congo red from aqueous solution on hydroxyapatite].

PubMed

Zhan, Yan-Hui; Lin, Jian-Wei

2013-08-01

The adsorption of Congo red (CR) from aqueous solution on hydroxyapatite was investigated using batch experiments. The hydroxyapatite was effective for CR removal from aqueous solution. The adsorption kinetics of CR on hydroxyapatite well followed a pseudo-second-order model. The equilibrium adsorption data of CR on hydroxyapatite could be described by the Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherm models. Thermodynamic parameters such as Gibbs free energy change, enthalpy change and entropy change were calculated and showed that the adsorption of CR on hydroxyapatite was spontaneous and exothermic in nature. The CR adsorption capacity for hydroxyapatite decreased significantly with increasing pH from 8 to 10. Thermal regeneration showed that hydroxyapatite could be used for six desorption-adsorption cycles with high removal efficiency for CR in each cycle. The mechanisms for CR adsorption on hydroxyapatite with pH value below the pH at point of zero charge (pH(PZC)) include electrostatic attraction, hydrogen bonding and Lewis acid-base interaction. The mechanisms for CR adsorption on hydroxyapatite with pH value above its pH(PZC) include hydrogen bonding and Lewis acid-base interaction. Results of this work indicate that hydroxyapatite is a promising adsorbent for CR removal from aqueous solution.

Perfluorooctane sulfonate adsorption on powder activated carbon: Effect of phosphate (P) competition, pH, and temperature.

PubMed

Qian, Jin; Shen, Mengmeng; Wang, Peifang; Wang, Chao; Li, Kun; Liu, Jingjing; Lu, Bianhe; Tian, Xin

2017-09-01

Powdered activated carbon (PAC), as an adsorbent, was applied to remove perfluorooctane sulfonate (PFOS) from aqueous solution. Laboratory batch experiments were performed to investigate the influences of phosphate (P) competition, temperature, and pH for PFOS adsorption onto PAC. The results showed that higher temperature favored PFOS adsorption in single and binary systems. The kinetic data fitted very well to the pseudo second-order kinetic model. Thermodynamically, the endothermic enthalpy of the PFOS adsorption in single and binary systems were 125.07 and 21.25 kJ mol -1 , respectively. The entropy of the PFOS adsorption in single and binary systems were 0.479 and 0.092 kJ mol -1  K -1 , respectively. And the Gibbs constants were negative. These results indicated that the adsorption processes were spontaneous. The adsorption isotherms of PFOS agreed well with the Langmuir model. In the single system, PFOS adsorption decreased with increased pH value. The difference in the amount of PFOS adsorption between the single and binary systems increased at higher pH. Frustrated total internal reflection (FTIR) demonstrated that P competition increased the hydrophilicity of the PAC and the electrostatic repulsion between PFOS and PAC, then the PFOS adsorption amount decreased. It also demonstrated that, at higher temperature, increased PFOS adsorption was mainly due to the higher diffusion rate of PFOS molecules and greater number of active sites opened on the PAC surface. Copyright © 2017 Elsevier Ltd. All rights reserved.

The surface characteristics of hyperbranched polyamide modified corncob and its adsorption property for Cr(VI)

NASA Astrophysics Data System (ADS)

Lin, Hai; Han, Shaoke; Dong, Yingbo; He, Yinhai

2017-08-01

A low-cost anion adsorbent for Cr(VI) effectively removing was synthesized by hyperbranched polyamide modified corncob (HPMC). Samples were characterized by Brunauer-Emmett-Teller (BET) surface area analysis, field-emission scanning electron microscopy (FE-SEM) with energy-dispersive X-ray spectroscopy, Fourier transform infrared (FTIR) and zeta potential analysis. Kinetics, isotherms and thermodynamics studies of HPMC for Cr(VI) adsorption were investigated in batch static experiments, in the temperature range of 25-45 °C, pH = 2.0. Results showed that the adsorption was rapid and stable, with the uptake capacity higher than 80% after 30 min. Adsorption behavior and rate-controlling mechanisms were analyzed using three kinetic models (pseudo-first order, pseudo-second order, intra-particle kinetic model). Kinetic studies showed that the adsorption of HPMC to Cr(VI) relied the pseudo-second-order model, and controlled both by the intra-particle diffusion and film diffusion. Equilibrium data was tested by Langmuir and Freundlich adsorption isotherm models. Langmuir model was more suitable to indicate a homogeneous distribution of active sites on HPMC and monolayer adsorption. The maximum adsorption capacity from the Langmuir model, qmax, was 131.6 mg/g at pH 2.0 and 45 °C for HPMC. Thermodynamic parameters revealed spontaneous and endothermic nature of the Cr(VI) adsorption onto HPMC.

On irreversible adsorption of electron-donating compounds in aqueous solution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tamon, Hajime; Atsushi, Masanori; Okazaki, Morio

Activated carbons and synthetic adsorbents have been used for liquid purification and wastewater treatment. The feasibility of an adsorption process depends greatly on the cost of regeneration of spent adsorbents. If irreversible adsorption occurs, regeneration of spent adsorbent is very difficult. Hence, it is very important to understand why irreversible adsorption appears in aqueous solution. In the adsorption of electron-donating compounds such as phenol, aniline, L-phenylalanine, and L-tyrosine from aqueous solution, irreversibility was observed on activated carbon and graphite. The compounds, except L-tyrosine, were reversibly adsorbed on a synthetic adsorbent. In the case where the carbonaceous adsorbents contacted the aqueousmore » solution containing electron-donating compounds for a long time, the irreversible amount adsorbed increased with the contact time. A two-state adsorption model was used to explain why the irreversible adsorption of electron-donating compound appears in aqueous solution. First, the compound is adsorbed in the precursor state for irreversible adsorption, and then moves into its irreversible state over a potential energy barrier after a long contact time. The appearance of irreversible adsorption was qualitatively explained by the two-state adsorption model.« less

Protein adsorption in microengraving immunoassays.

PubMed

Song, Qing

2015-10-16

Microengraving is a novel immunoassay for characterizing multiple protein secretions from single cells. During the immunoassay, characteristic diffusion and kinetic time scales  and  determine the time for molecular diffusion of proteins secreted from the activated single lymphocytes and subsequent binding onto the glass slide surface respectively. Our results demonstrate that molecular diffusion plays important roles in the early stage of protein adsorption dynamics which shifts to a kinetic controlled mechanism in the later stage. Similar dynamic pathways are observed for protein adsorption with significantly fast rates and rapid shifts in transport mechanisms when  is increased a hundred times from 0.313 to 31.3. Theoretical adsorption isotherms follow the trend of experimentally obtained data. Adsorption isotherms indicate that amount of proteins secreted from individual cells and subsequently captured on a clean glass slide surface increases monotonically with time. Our study directly validates that protein secretion rates can be quantified by the microengraving immunoassay. This will enable us to apply microengraving immunoassays to quantify secretion rates from 10⁴-10⁵ single cells in parallel, screen antigen-specific cells with the highest secretion rate for clonal expansion and quantitatively reveal cellular heterogeneity within a small cell sample.

Protein Adsorption in Microengraving Immunoassays

PubMed Central

Song, Qing

2015-01-01

Microengraving is a novel immunoassay forcharacterizing multiple protein secretions from single cells. During the immunoassay, characteristic diffusion and kinetic time scales τD and τK determine the time for molecular diffusion of proteins secreted from the activated single lymphocytes and subsequent binding onto the glass slide surface respectively. Our results demonstrate that molecular diffusion plays important roles in the early stage of protein adsorption dynamics which shifts to a kinetic controlled mechanism in the later stage. Similar dynamic pathways are observed for protein adsorption with significantly fast rates and rapid shifts in transport mechanisms when C0* is increased a hundred times from 0.313 to 31.3. Theoretical adsorption isotherms follow the trend of experimentally obtained data. Adsorption isotherms indicate that amount of proteins secreted from individual cells and subsequently captured on a clean glass slide surface increases monotonically with time. Our study directly validates that protein secretion rates can be quantified by the microengraving immunoassay. This will enable us to apply microengraving immunoassays to quantify secretion rates from 104–105 single cells in parallel, screen antigen-specific cells with the highest secretion rate for clonal expansion and quantitatively reveal cellular heterogeneity within a small cell sample. PMID:26501282

Sodium dodecyl sulfate-ethoxylated polyethylenimine adsorption at the air-water interface: how the nature of ethoxylation affects the pattern of adsorption.

PubMed

Batchelor, Stephen N; Tucker, Ian; Petkov, Jordan T; Penfold, Jeffrey; Thomas, Robert K

2014-08-19

The strong interaction between ionic surfactants and polyelectrolytes of opposite charge results in enhanced surface adsorption at the air-water interface down to low surfactant concentrations and in some cases in the formation of ordered surface structures. A notable example which exhibits such properties is the mixture of polyethylenimine, PEI, and sodium dodecyl sulfate, SDS. However, the electrostatic interaction, around charge neutralization, between the surfactant and polymer often results in precipitation or coacervation. This can be mitigated for PEI-surfactant mixtures by ethoxylation of the PEI, but this can also result in a weaker surface interaction and a significant reduction in the adsorption. It is shown here that by localizing the ethoxylation of the PEI into discrete regions of the polymer precipitation upon the addition of SDS is suppressed, the strong surface interaction and enhanced adsorption of the polymer-surfactant mixture is retained. The adsorption of SDS in the presence of ethoxylated PEI is greatly enhanced at low SDS concentrations compared to the adsorption for pure SDS. The adsorption is equally pronounced at pH 7 and 10 and is largely independent of the degree of ethoxylation. Surface ordering, more than monolayer adsorption, is observed over a relatively narrow range of SDS concentrations and is most pronounced at pH 10 and for the polymers with the lower degree of ethoxylation. The results show that ethoxylated PEI's reported here provide a suitable route to enhanced surfactant adsorption while retaining favorable solution properties in which precipitation effects are minimized.

Adsorption and dissociation of molecular oxygen on α-Pu (0 2 0) surface: A density functional study

NASA Astrophysics Data System (ADS)

Wang, Jianguang; Ray, Asok K.

2011-09-01

Molecular and dissociative oxygen adsorptions on the α-Pu (0 2 0) surface have been systematically studied using the full-potential linearized augmented-plane-wave plus local orbitals (FP-LAPW+lo) basis method and the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional. Chemisorption energies have been optimized for the distance of the admolecule from the Pu surface and the bond length of O-O atoms for four adsorption sites and three approaches of O 2 admolecule to the (0 2 0) surface. Chemisorption energies have been calculated at the scalar relativistic level with no spin-orbit coupling (NSOC) and at the fully relativistic level with spin-orbit coupling (SOC). Dissociative adsorptions are found at the two horizontal approaches (O 2 is parallel to the surface and perpendicular/parallel to a lattice vector). Hor2 (O 2 is parallel to the surface and perpendicular to a lattice vector) approach at the one-fold top site is the most stable adsorption site, with chemisorption energies of 8.048 and 8.415 eV for the NSOC and SOC cases, respectively, and an OO separation of 3.70 Å. Molecular adsorption occurs at the Vert (O 2 is vertical to the surface) approach of each adsorption site. The calculated work functions and net spin magnetic moments, respectively, increase and decrease in all cases upon chemisorption compared to the clean surface. The partial charges inside the muffin-tins, the difference charge density distributions, and the local density of states have been used to investigate the Pu-admolecule electronic structures and bonding mechanisms.

Properties and reactivity of Fe-organic matter associations formed by coprecipitation versus adsorption: Clues from arsenate batch adsorption

NASA Astrophysics Data System (ADS)

Mikutta, Robert; Lorenz, Dennis; Guggenberger, Georg; Haumaier, Ludwig; Freund, Anja

2014-11-01

Ferric oxyhydroxides play an important role in controlling the bioavailability of oxyanions such as arsenate and phosphate in soil. Despite this, little is known about the properties and reactivity of Fe(III)-organic matter phases derived from adsorption (reaction of organic matter (OM) to post-synthesis Fe oxide) versus coprecipitation (formation of Fe oxides in presence of OM). Coprecipitates and adsorption complexes were synthesized at pH 4 using two natural organic matter (NOM) types extracted from forest floor layers (Oi and Oa horizon) of a Haplic Podzol. Iron(III) coprecipitates were formed at initial molar metal-to-carbon (M/C) ratios of 1.0 and 0.1 and an aluminum (Al)-to-Fe(III) ratio of 0.2. Sample properties were studied by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), N2 gas adsorption, dynamic light scattering, and electrophoretic mobility measurements. Arsenic [As(V)] adsorption to Fe-OM phases was studied in batch experiments (168 h, pH 4, 100 μM As). The organic carbon (OC) contents of the coprecipitates (82-339 mg g-1) were higher than those of adsorption complexes (31 and 36 mg g-1), leading to pronounced variations in specific surface area (9-300 m2 g-1), average pore radii (1-9 nm), and total pore volumes (11-374 mm3 g-1) but being independent of the NOM type or the presence of Al. The occlusion of Fe solids by OM (XPS surface concentrations: 60-82 atom% C) caused comparable pHPZC (1.5-2) of adsorption complexes and coprecipitates. The synthesis conditions resulted in different Fe-OM association modes: Fe oxide particles in 'M/C 0.1' coprecipitates covered to a larger extent the outermost aggregate surfaces, for some 'M/C 1.0' coprecipitates OM effectively enveloped the Fe oxides, while OM in the adsorption complexes primarily covered the outer aggregate surfaces. Despite of their larger OC contents, adsorption of As(V) was fastest to coprecipitates formed at low Fe availability (M/C 0.1) and facilitated by desorption of weakly

Surface complexation modeling calculation of Pb(II) adsorption onto the calcined diatomite

NASA Astrophysics Data System (ADS)

Ma, Shu-Cui; Zhang, Ji-Lin; Sun, De-Hui; Liu, Gui-Xia

2015-12-01

Removal of noxious heavy metal ions (e.g. Pb(II)) by surface adsorption of minerals (e.g. diatomite) is an important means in the environmental aqueous pollution control. Thus, it is very essential to understand the surface adsorptive behavior and mechanism. In this work, the Pb(II) apparent surface complexation reaction equilibrium constants on the calcined diatomite and distributions of Pb(II) surface species were investigated through modeling calculations of Pb(II) based on diffuse double layer model (DLM) with three amphoteric sites. Batch experiments were used to study the adsorption of Pb(II) onto the calcined diatomite as a function of pH (3.0-7.0) and different ionic strengths (0.05 and 0.1 mol L-1 NaCl) under ambient atmosphere. Adsorption of Pb(II) can be well described by Freundlich isotherm models. The apparent surface complexation equilibrium constants (log K) were obtained by fitting the batch experimental data using the PEST 13.0 together with PHREEQC 3.1.2 codes and there is good agreement between measured and predicted data. Distribution of Pb(II) surface species on the diatomite calculated by PHREEQC 3.1.2 program indicates that the impurity cations (e.g. Al3+, Fe3+, etc.) in the diatomite play a leading role in the Pb(II) adsorption and dominant formation of complexes and additional electrostatic interaction are the main adsorption mechanism of Pb(II) on the diatomite under weak acidic conditions.

The effect of high ionic strength on neptunium (V) adsorption to a halophilic bacterium

NASA Astrophysics Data System (ADS)

Ams, David A.; Swanson, Juliet S.; Szymanowski, Jennifer E. S.; Fein, Jeremy B.; Richmann, Michael; Reed, Donald T.

2013-06-01

The mobility of neptunium (V) in subsurface high ionic strength aqueous systems may be strongly influenced by adsorption to the cell wall of the halophilic bacteria Chromohalobacter sp. This study is the first to evaluate the adsorption of neptunium (V) to the surface of a halophilic bacterium as a function of pH from approximately 2 to 10 and at ionic strengths of 2 and 4 M. This is also the first study to evaluate the effects of carbonate complexation with neptunium (V) on adsorption to whole bacterial cells under high pH conditions. A thermodynamically-based surface complexation model was adapted to describe experimental adsorption data under high ionic strength conditions where traditional corrections for aqueous ion activity are invalid. Adsorption of neptunium (V) was rapid and reversible under the conditions of the study. Adsorption was significant over the entire pH range evaluated for both ionic strength conditions and was shown to be dependent on the speciation of the sites on the bacterial surface and neptunium (V) in solution. Adsorption behavior was controlled by the relatively strong electrostatic attraction of the positively charged neptunyl ion to the negatively charged bacterial surface at pH below circum-neutral. At pH above circum-neutral, the adsorption behavior was controlled by the presence of negatively charged neptunium (V) carbonate complexes resulting in decreased adsorption, although adsorption was still significant due to the adsorption of negatively charged neptunyl-carbonate species. Adsorption in 4 M NaClO4 was enhanced relative to adsorption in 2 M NaClO4 over the majority of the pH range evaluated, likely due to the effect of increasing aqueous ion activity at high ionic strength. The protonation/deprotonation characteristics of the cell wall of Chromohalobacter sp. were evaluated by potentiometric titrations in 2 and 4 M NaClO4. Bacterial titration results indicated that Chromohalobacter sp. exhibits similar proton buffering

Adsorption of small hydrocarbons on rutile TiO 2(110)

DOE PAGES

Chen, Long; Smith, R. Scott; Kay, Bruce D.; ...

2015-11-21

Here, temperature programmed desorption and molecular beam scattering were used to study the adsorption and desorption of small hydrocarbons (n-alkanes, 1-alkenes and 1-alkynes of C 1–C 4) on rutile TiO 2(110). We show that the sticking coefficients for all the hydrocarbons are close to unity (> 0.95) at an adsorption temperature of 60 K. The desorption energies for hydrocarbons of the same chain length increase from n-alkanes to 1-alkenes and to 1-alkynes. This trend is likely a consequence of additional dative bonding of the alkene and alkyne π system to the coordinatively unsaturated Ti 5c sites. Similar to previous studiesmore » on the adsorption of n-alkanes on metal and metal oxide surfaces, we find that the desorption energies within each group (n-alkanes vs. 1-alkenes vs. 1-alkynes) from Ti 5c sites increase linearly with the chain length. The absolute saturation coverages of each hydrocarbon on Ti 5c sites were also determined. The saturation coverage of CH 4, is found to be ~ 2/3 monolayer (ML). The saturation coverages of C 2–C 4 hydrocarbons are found nearly independent of the chain length with values of ~ 1/2 ML for n-alkanes and 1-alkenes and 2/3 ML for 1-alkynes. This result is surprising considering their similar sizes.« less

Single-Molecule Probing of Adsorption and Diffusion on Silica Surfaces

NASA Astrophysics Data System (ADS)

Wirth, Mary J.; Legg, Michael A.

2007-05-01

Single-molecule spectroscopy has emerged as a valuable tool in probing kinetics and dynamic equilibria in adsorption because advances in instrumentation and technology have enabled researchers to obtain high signal-to-noise ratios for common dyes at room temperature. Single-molecule spectroscopy was applied to the study of an important problem in chromatography: peak broadening and asymmetry in the chromatograms of pharmaceuticals, peptides, and proteins. Using DiI, a cationic dye that exhibits the same problematic chromatographic behavior, investigators showed that the adsorption sites that cause chromatographic problems are located at defects on the silica crystal surface.

Predicting mixed-gas adsorption equilibria on activated carbon for precombustion CO2 capture.

PubMed

García, S; Pis, J J; Rubiera, F; Pevida, C

2013-05-21

We present experimentally measured adsorption isotherms of CO2, H2, and N2 on a phenol-formaldehyde resin-based activated carbon, which had been previously synthesized for the separation of CO2 in a precombustion capture process. The single component adsorption isotherms were measured in a magnetic suspension balance at three different temperatures (298, 318, and 338 K) and over a large range of pressures (from 0 to 3000-4000 kPa). These values cover the temperature and pressure conditions likely to be found in a precombustion capture scenario, where CO2 needs to be separated from a CO2/H2/N2 gas stream at high pressure (~1000-1500 kPa) and with a high CO2 concentration (~20-40 vol %). Data on the pure component isotherms were correlated using the Langmuir, Sips, and dual-site Langmuir (DSL) models, i.e., a two-, three-, and four-parameter model, respectively. By using the pure component isotherm fitting parameters, adsorption equilibrium was then predicted for multicomponent gas mixtures by the extended models. The DSL model was formulated considering the energetic site-matching concept, recently addressed in the literature. Experimental gas-mixture adsorption equilibrium data were calculated from breakthrough experiments conducted in a lab-scale fixed-bed reactor and compared with the predictions from the models. Breakthrough experiments were carried out at a temperature of 318 K and five different pressures (300, 500, 1000, 1500, and 2000 kPa) where two different CO2/H2/N2 gas mixtures were used as the feed gas in the adsorption step. The DSL model was found to be the one that most accurately predicted the CO2 adsorption equilibrium in the multicomponent mixture. The results presented in this work highlight the importance of performing experimental measurements of mixture adsorption equilibria, as they are of utmost importance to discriminate between models and to correctly select the one that most closely reflects the actual process.

Albumin adsorption onto surfaces of urine collection and analysis containers☆

PubMed Central

Robinson, Mary K.; Caudill, Samuel P.; Koch, David D.; Ritchie, James; Hortin, Glen; Eckfeldt, John H.; Sandberg, Sverre; Williams, Desmond; Myers, Gary; Miller, W. Greg

2017-01-01

Background Adsorption of albumin onto urine collection and analysis containers may cause falsely low concentrations. Methods We added 125I-labeled human serum albumin to urine and to phosphate buffered solutions, incubated them with 22 plastic container materials and measured adsorption by liquid scintillation counting. Results Adsorption of urine albumin (UA) at 5–6 mg/l was <0.9%; and at 90 mg/l was <0.4%. Adsorption was generally less at pH 8 than pH 5 but only 3 cases had p <0.05. Adsorption from 11 unaltered urine samples with albumin 5–333 mg/l was <0.8%. Albumin adsorption for the material with greatest binding was extrapolated to the surface areas of 100 ml and 2 l collection containers, and to instrument sample cups and showed <1% change in concentration at 5 mg/l and <0.5% change at 20 mg/l or higher concentrations. Adsorption of albumin from phosphate buffered solutions (2–28%) was larger than that from urine. Conclusions Albumin adsorption differed among urine samples and plastic materials, but the total influence of adsorption was <1% for all materials and urine samples tested. Adsorption of albumin from phosphate buffered solutions was larger than that from urine and could be a limitation for preparations used as calibrators. PMID:24513540

Albumin adsorption onto surfaces of urine collection and analysis containers.

PubMed

Robinson, Mary K; Caudill, Samuel P; Koch, David D; Ritchie, James; Hortin, Glen; Eckfeldt, John H; Sandberg, Sverre; Williams, Desmond; Myers, Gary; Miller, W Greg

2014-04-20

Adsorption of albumin onto urine collection and analysis containers may cause falsely low concentrations. We added (125)I-labeled human serum albumin to urine and to phosphate buffered solutions, incubated them with 22 plastic container materials and measured adsorption by liquid scintillation counting. Adsorption of urine albumin (UA) at 5-6 mg/l was <0.9%; and at 90 mg/l was <0.4%. Adsorption was generally less at pH8 than pH5 but only 3 cases had p<0.05. Adsorption from 11 unaltered urine samples with albumin 5-333 mg/l was <0.8%. Albumin adsorption for the material with greatest binding was extrapolated to the surface areas of 100 ml and 2l collection containers, and to instrument sample cups and showed <1% change in concentration at 5 mg/l and <0.5% change at 20 mg/l or higher concentrations. Adsorption of albumin from phosphate buffered solutions (2-28%) was larger than that from urine. Albumin adsorption differed among urine samples and plastic materials, but the total influence of adsorption was <1% for all materials and urine samples tested. Adsorption of albumin from phosphate buffered solutions was larger than that from urine and could be a limitation for preparations used as calibrators. Copyright © 2014 Elsevier B.V. All rights reserved.

Adsorption of SOx and NOx in activated viscose fibers.

PubMed

Plens, Ana Carolina O; Monaro, Daniel L G; Coutinho, Aparecido R

2015-01-01

SOx and NOx are emissions resulting from combustion processes and are the main agents that contribute to the formation of acid rain, which causes harm to humans and the environment. Several techniques for removing these pollutants are applied in i.e. oil refineries, thermoelectric that use petroleum oils and vehicular pollution. Among these, highlight the adsorption of contaminants by the usage of activated carbon fibers and activated carbon, which are characterized by high surface area and uniform distribution of pores, providing appropriate conditions for application in processes of removing environmental contaminants. In the present work, activated viscose fibers (AVF) were prepared and applied in adsorption experiments of NO and SO2. The materials produced showed high values of surface area, with a predominance of micro pores with diameters in the range of 1.0 nm. The AVF had satisfactory performance in the removal of contaminants and are compatible with other synthetic fibers. Thus, the formation of active sites of carbon provides contaminants adsorption, demonstrating that carbon fibers cloth can be applied for the removal of pollutants.

Hydrogen adsorption site on the Ni?110?-p(1 × 2)-H surface from time-of-flight scattering and recoiling spectrometry (TOF-SARS)

NASA Astrophysics Data System (ADS)

Bu, H.; Roux, C. D.; Rabalais, J. W.

The adsorption site of hydrogen on the Ni{110}-p(1 × 2)-H surface resulting from saturation exposure to H 2 at ˜ 310-350 K has been investigated by time-of-flight scattering and recoiling spectrometry (TOF-SARS). The recoiled neutral plus ion hydrogen atom flux resulting from 2-5 keV Ar + or Ne + pulsed ion beams incident on the surface was monitored as a function of crystal azimuthal angle and beam incidence angle. From classical trajectory calculations and shadowing and blocking analyses, it is concluded that hydrogen atoms are localized at the pseudo-three-fold sites on the (1 × 2) missing-row (MR) reconstructed Ni{110} surface; the (1 × 2) MR reconstruction is induced by hydrogen adsorption shown elsewhere [Surf. Sci. 259 (1991) 253]. Only the pseudo-three-fold site is consistent with all of the experimental data. The coordinates of the hydrogen adsorption site with respect to the nickel lattice were determined. The lateral distance of hydrogen from the 1st-layer Ni <1 overline10> rows is 1.56 ± 0.12 Å and the vertical distance above the substrate is 0.21 ± 0.12 Å, providing NiH bond lengths of 2.0 Å to the two-layer Ni atoms and 1.5 Å to the 2nd-layer Ni atom.

CoFe2O4@MIL-100(Fe) hybrid magnetic nanoparticles exhibit fast and selective adsorption of arsenic with high adsorption capacity

PubMed Central

Yang, Ji-Chun; Yin, Xue-Bo

2017-01-01

In this study, we report the synthesis and application of mesoporous CoFe2O4@MIL-100(Fe) hybrid magnetic nanoparticles (MNPs) for the simultaneous removal of inorganic arsenic (iAs). The hybrid adsorbent had a core-shell and mesoporous structure with an average diameter of 260 nm. The nanoscale size and mesoporous character impart a fast adsorption rate and high adsorption capacity for iAs. In total, 0.1 mg L−1 As(V) and As(III) could be adsorbed within 2 min, and the maximum adsorption capacities were 114.8 mg g−1 for As(V) and 143.6 mg g−1 for As(III), higher than most previously reported adsorbents. The anti-interference capacity for iAs adsorption was improved by the electrostatic repulsion and size exclusion effects of the MIL-100(Fe) shell, which also decreased the zero-charge point of the hybrid absorbent for a broad pH adsorption range. The adsorption mechanisms of iAs on the MNPs are proposed. An Fe-O-As structure was formed on CoFe2O4@MIL-100(Fe) through hydroxyl substitution with the deprotonated iAs species. Monolayer adsorption of As(V) was observed, while hydrogen bonding led to the multi-layer adsorption of neutral As(III) for its high adsorption capacity. The high efficiency and the excellent pH- and interference-tolerance capacities of CoFe2O4@MIL-100(Fe) allowed effective iAs removal from natural water samples, as validated with batch magnetic separation mode and a portable filtration strategy. PMID:28102334

CoFe2O4@MIL-100(Fe) hybrid magnetic nanoparticles exhibit fast and selective adsorption of arsenic with high adsorption capacity

NASA Astrophysics Data System (ADS)

Yang, Ji-Chun; Yin, Xue-Bo

2017-01-01

In this study, we report the synthesis and application of mesoporous CoFe2O4@MIL-100(Fe) hybrid magnetic nanoparticles (MNPs) for the simultaneous removal of inorganic arsenic (iAs). The hybrid adsorbent had a core-shell and mesoporous structure with an average diameter of 260 nm. The nanoscale size and mesoporous character impart a fast adsorption rate and high adsorption capacity for iAs. In total, 0.1 mg L-1 As(V) and As(III) could be adsorbed within 2 min, and the maximum adsorption capacities were 114.8 mg g-1 for As(V) and 143.6 mg g-1 for As(III), higher than most previously reported adsorbents. The anti-interference capacity for iAs adsorption was improved by the electrostatic repulsion and size exclusion effects of the MIL-100(Fe) shell, which also decreased the zero-charge point of the hybrid absorbent for a broad pH adsorption range. The adsorption mechanisms of iAs on the MNPs are proposed. An Fe-O-As structure was formed on CoFe2O4@MIL-100(Fe) through hydroxyl substitution with the deprotonated iAs species. Monolayer adsorption of As(V) was observed, while hydrogen bonding led to the multi-layer adsorption of neutral As(III) for its high adsorption capacity. The high efficiency and the excellent pH- and interference-tolerance capacities of CoFe2O4@MIL-100(Fe) allowed effective iAs removal from natural water samples, as validated with batch magnetic separation mode and a portable filtration strategy.

Effects of Hydration and Oxygen Vacancy on CO2 Adsorption and Activation on β-Ga2O3(100)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pan, Yunxiang; Liu, Chang-jun; Mei, Donghai

The effects of hydration and oxygen vacancy on CO2 adsorption on the β-Ga2O3(100) surface have been studied using density functional theory slab calculations. Adsorbed CO2 is activated on the dry perfect β-Ga2O3(100) surface, resulting in a carbonate species. This adsorption is slightly endothermic, with an adsorption energy of 0.07 eV. Water is preferably adsorbed molecularly on the dry perfect β-Ga2O3(100) surface with an adsorption energy of -0.56 eV, producing a hydrated perfect β-Ga2O3(100) surface. Adsorption of CO2 on the hydrated surface as a carbonate species is also endothermic, with an adsorption energy of 0.14 eV, indicating a slight repulsive interactionmore » when H2O and CO2 are coadsorbed. The carbonate species on the hydrated perfect surface can be protonated by the co-adsorbed H2O to a bicarbonate species, making the overall process exothermic with an adsorption energy of -0.13 eV. The effect of defects on CO2 adsorption and activation has been examined by creating an oxygen vacancy on the dry β-Ga2O3(100) surface. The formation of an oxygen vacancy is endothermic, by 0.34 eV, with respect to a free O2 molecule in the gas phase. Presence of the oxygen vacancy promoted the adsorption and activation of CO2. In the most stable CO2 adsorption configuration on the dry defective β-Ga2O3(100) surface with an oxygen vacancy, one of the oxygen atoms of the adsorbed CO2 occupies the oxygen vacancy site and the CO2 adsorption energy is -0.31 eV. Water favors dissociative adsorption at the oxygen vacancy site on the defective surface. This process is instantaneous with an adsorption energy of -0.62 eV. These results indicate that, when water and CO2 are both present in the adsorption system simultaneously, the water molecule will compete with CO2 for the oxygen vacancy sites and impact CO2 adsorption and conversion negatively. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy. A portion of the computing time

Adsorption of Organics from Domestic Water Supplies.

ERIC Educational Resources Information Center

McGuire, Michael J.; Suffet, Irwin H.

1978-01-01

This article discusses the current state of the art of organics removal by adsorption. Various theoretical explanations of the adsorption process are given, along with practical results from laboratory, pilot-scale, and full-scale applications. (CS)

Single, competitive, and dynamic adsorption on activated carbon of compounds used as plasticizers and herbicides.

PubMed

Abdel daiem, Mahmoud M; Rivera-Utrilla, José; Sánchez-Polo, Manuel; Ocampo-Pérez, Raúl

2015-12-15

The main aim of this study was to investigate the single, competitive, and dynamic adsorption of phthalic acid (PA), bisphenol A (BPA), diphenolic acid (DPA), 2,4-dichlorophenoxy-acetic acid (2,4-D), and 4-chloro-2-methylphenoxyacetic acid (MCPA) on two activated carbons with different chemical natures and similar textural characteristics. The adsorption mechanism was also elucidated by analyzing the influence of solution pH and ionic strength. The activated carbons demonstrated high adsorption capacity to remove all micropollutants due to the presence of active sites on their surfaces, which increase dispersive interactions between the activated carbon graphene layers and the aromatic ring of pollutants. The adsorption capacity of the activated carbons increased in the order: DPAadsorption of contaminants is favored at acid pH (pH<5) due to the establishment of attractive electrostatic interactions. In dynamic regime, the amount of pollutant adsorbed was much higher for PA, followed by DPA, and was approximately similar for BPA, 2,4-D, and MCPA. Finally, the amount of BPA and DPA adsorbed on activated carbon decreased by around 50% and 70% in the presence of DPA and BPA, respectively, indicating that both compounds are adsorbed on the same adsorption sites of the activated carbon. Copyright © 2015 Elsevier B.V. All rights reserved.

Modification of polystyrene-based activated carbon spheres to improve adsorption of dibenzothiophene

NASA Astrophysics Data System (ADS)

Wang, Qin; Liang, Xiaoyi; Qiao, Wenming; Liu, Chaojun; Liu, Xiaojun; Zhang, Rui; Ling, Licheng

2009-01-01

Polystyrene-based activated carbon spheres (PACS) were modified with either air, HNO 3, (NH 4) 2S 2O 8, H 2O 2 or H 2 to improve their adsorption properties of dibenzothiophene (DBT). The texture and surface chemistry of PACS were characterized by N 2 adsorption, scanning electron microscopy (SEM), temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), acid-base titration and elemental analysis. The results showed that HNO 3 and (NH 4) 2S 2O 8 treatments introduced large amount of acidic groups such as carboxylic, lactones and anhydride groups, while air and H 2O 2 had relatively mild effects and introduced a small quantity of phenol, carbonyl and ether groups. In the HNO 3 treatment, the acidic groups might be fixed on the internal and external surface of PACS, which may act as active sites of adsorption, resulting in increase of the adsorption amount by 45%. Whereas H 2O 2 and (NH 4) 2S 2O 8 treatments might fix more oxygen-containing groups on the external surface, which may hinder DBT molecule enter into micropores, leading to rather lower adsorption capacity with the extent of oxidation. So, the concentration, distribution and types of the acidic functional groups are responsible for the removal of DBT.

Adsorption of alkali and alkaline earth metal atoms and dimers on monolayer germanium carbide

NASA Astrophysics Data System (ADS)

Gökçe, Aytaç Gürhan; Ersan, Fatih

2017-01-01

First-principles plane wave calculations have been performed to study the adsorption of alkali and alkaline earth metals on monolayer germanium carbide (GeC). We found that the favourable adsorption sites on GeC sheet for single alkali and alkaline earth adatoms are generally different from graphene or germanene. Among them, Mg, Na and their dimers have weakly bounded to GeC due to their closed valence electron shells, so they may have high mobility on GeC. Two different levels of adatom coverage (? and ?) have been investigated and we concluded that different electronic structures and magnetic moments for both coverages owing to alkali and alkaline earth atoms have long range electrostatic interactions. Lithium atom prefers to adsorbed on hollow site similar to other group-IV monolayers and the adsorption results in metallisation of GeC instead of semiconducting behaviour. Na and K adsorption can induce 1 ? total magnetic moment on GeC structures and they have shown semiconductor property which may have potential use in spintronic devices. We also showed that alkali or alkaline earth metal atoms can form dimer on GeC sheet. Calculated adsorption energies suggest that clustering of alkali and alkaline earth atoms is energetically favourable. All dimer adsorbed GeC systems have nonmagnetic semiconductor property with varying band gaps from 0.391 to 1.311 eV which are very suitable values for various device applications.

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

PubMed Central

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

2008-01-01

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

Hydrogen adsorption in metal-decorated silicon carbide nanotubes

NASA Astrophysics Data System (ADS)

Singh, Ram Sevak; Solanki, Ankit

2016-09-01

Hydrogen storage for fuel cell is an active area of research and appropriate materials with excellent hydrogen adsorption properties are highly demanded. Nanotubes, having high surface to volume ratio, are promising storage materials for hydrogen. Recently, silicon carbide nanotubes have been predicted as potential materials for future hydrogen storage application, and studies in this area are ongoing. Here, we report a systematic study on hydrogen adsorption properties in metal (Pt, Ni and Al) decorated silicon carbide nanotubes (SiCNTs) using first principles calculations based on density functional theory. The hydrogen adsorption properties are investigated by calculations of adsorption energy, electronic band structure, density of states (DOS) and Mulliken charge population analysis. Our findings show that hydrogen adsorptions on Pt, Ni and Al-decorated SiCNTs undergo spontaneous exothermic reactions with significant modulation of electronic structure of SiCNTs in all cases. Importantly, according to the Mulliken charge population analysis, dipole-dipole interaction causes chemisorptions of hydrogen in Pt, Ni and Al decorated SiCNTs with formation of chemical bonds. The study is a platform for the development of metal decorated SiCNTs for hydrogen adsorption or hydrogen storage application.

CONTAMINANT ADSORPTION AND OXIDATION VIA FENTON REACTION

EPA Science Inventory

A ground water treatment process is proposed involving two cgemical processes: adsorption and oxidation. Adsorption of an organic compound onto granulated activated carbon (GAC) containing iron conveniently results in immobilizing and concentrating contaminants from the ground w...

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

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

1999-02-01

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

Modeling adsorption with lattice Boltzmann equation

PubMed Central

Guo, Long; Xiao, Lizhi; Shan, Xiaowen; Zhang, Xiaoling

2016-01-01

The research of adsorption theory has recently gained renewed attention due to its critical relevance to a number of trending industrial applications, hydrogen storage and shale gas exploration for instance. The existing theoretical foundation, laid mostly in the early twentieth century, was largely based on simple heuristic molecular interaction models and static interaction potential which, although being insightful in illuminating the fundamental mechanisms, are insufficient for computations with realistic adsorbent structure and adsorbate hydrodynamics, both critical for real-life applications. Here we present and validate a novel lattice Boltzmann model incorporating both adsorbate-adsorbate and adsorbate-adsorbent interactions with hydrodynamics which, for the first time, allows adsorption to be computed with real-life details. Connection with the classic Ono-Kondo lattice theory is established and various adsorption isotherms, both within and beyond the IUPAC classification are observed as a pseudo-potential is varied. This new approach not only enables an important physical to be simulated for real-life applications, but also provides an enabling theoretical framework within which the fundamentals of adsorption can be studied. PMID:27256325

Heat of adsorption, adsorption stress, and optimal storage of methane in slit and cylindrical carbon pores predicted by classical density functional theory.

PubMed

Hlushak, Stepan

2018-01-03

Temperature, pressure and pore-size dependences of the heat of adsorption, adsorption stress, and adsorption capacity of methane in simple models of slit and cylindrical carbon pores are studied using classical density functional theory (CDFT) and grand-canonical Monte-Carlo (MC) simulation. Studied properties depend nontrivially on the bulk pressure and the size of the pores. Heat of adsorption increases with loading, but only for sufficiently narrow pores. While the increase is advantageous for gas storage applications, it is less significant for cylindrical pores than for slits. Adsorption stress and the average adsorbed fluid density show oscillatory dependence on the pore size and increase with bulk pressure. Slit pores exhibit larger amplitude of oscillations of the normal adsorption stress with pore size increase than cylindrical pores. However, the increase of the magnitude of the adsorption stress with bulk pressure increase is more significant for cylindrical than for slit pores. Adsorption stress appears to be negative for a wide range of pore sizes and external conditions. The pore size dependence of the average delivered density of the gas is analyzed and the optimal pore sizes for storage applications are estimated. The optimal width of slit pore appears to be almost independent of storage pressure at room temperature and pressures above 10 bar. Similarly to the case of slit pores, the optimal radius of cylindrical pores does not exhibit much dependence on the storage pressure above 15 bar. Both optimal width and optimal radii of slit and cylindrical pores increase as the temperature decreases. A comparison of the results of CDFT theory and MC simulations reveals subtle but important differences in the underlying fluid models employed by the approaches. The differences in the high-pressure behaviour between the hard-sphere 2-Yukawa and Lennard-Jones models of methane, employed by the CDFT and MC approaches, respectively, result in an overestimation of

Volatile organic compound adsorption in a gas-solid fluidized bed.

PubMed

Ng, Y L; Yan, R; Tsen, L T S; Yong, L C; Liu, M; Liang, D T

2004-01-01

Fluidization finds many process applications in the areas of catalytic reactions, drying, coating, combustion, gasification and microbial culturing. This work aims to compare the dynamic adsorption characteristics and adsorption rates in a bubbling fluidized bed and a fixed bed at the same gas flow-rate, gas residence time and bed height. Adsorption with 520 ppm methanol and 489 ppm isobutane by the ZSM-5 zeolite of different particle size in the two beds enabled the differentiation of the adsorption characteristics and rates due to bed type, intraparticle mass transfer and adsorbate-adsorbent interaction. Adsorption of isobutane by the more commonly used activated carbon provided the comparison of adsorption between the two adsorbent types. With the same gas residence time of 0.79 seconds in both the bubbling bed and fixed bed of the same bed size of 40 mm diameter and 48 mm height, the experimental results showed a higher rate of adsorption in the bubbling bed as compared to the fixed bed. Intraparticle mass transfer and adsorbent-adsorbate interaction played significant roles in affecting the rate of adsorption, with intraparticle mass transfer being more dominant. The bubbling bed was observed to have a steeper decline in adsorption rate with respect to increasing outlet concentration compared to the fixed bed. The adsorption capacities of zeolite for the adsorbates studied were comparatively similar in both beds; fluidizing, and using smaller particles in the bubbling bed did not increase the adsorption capacity of the ZSM-5 zeolite. The adsorption capacity of activated carbon for isobutane was much higher than the ZSM-5 zeolite for isobutane, although at a lower adsorption rate. Fourier transform infra-red (FTIR) spectroscopy was used as an analytical tool for the quantification of gas concentration. Calibration was done using a series of standards prepared by in situ dilution with nitrogen gas, based on the ideal gas law and relating partial pressure to gas

Adsorption and desorption characteristics of arsenic onto ceria nanoparticles

PubMed Central

2012-01-01

The rapid increase in the use of engineered nanoparticles [ENPs] has resulted in an increasing concern over the potential impacts of ENPs on the environmental and human health. ENPs tend to adsorb a large variety of toxic chemicals when they are emitted into the environment, which may enhance the toxicity of ENPs and/or adsorbed chemicals. The study was aimed to investigate the adsorption and desorption behaviors of arsenic on ceria NPs in aqueous solution using batch technique. Results show that the adsorption behavior of arsenic on ceria NPs was strongly dependent on pH and independent of ionic strength, indicating that the electrostatic effect on the adsorption of these elements was relatively not important compared to surface chemical reactions. The adsorption isotherms fitted very well to both the Langmuir and Freundlich models. The thermodynamic parameters (ΔH0, ΔS0, and ΔG0) for the adsorption of arsenic were determined at three different temperatures of 283, 303, and 323 K. The adsorption reaction was endothermic, and the process of adsorption was favored at high temperature. The desorption data showed that desorption hysteresis occurred at the initial concentration studied. High adsorption capacity of arsenic on ceria NPs suggests that the synergistic effects of ceria NPs and arsenic on the environmental systems may exist when they are released into the environment. PMID:22269298

ADSORPTION TECHNOLOGIES

EPA Science Inventory

A 45 minute PPT presentation will be given at three training courses sponsored by the OGWDW, OW, USEPA. Courses are being held at Phoenix, AZ on April 25; Sacramento, CA on April 29; and South Bend, IN on May 9.

The presentation provides an overview of adsorptive media te...

Modeling adsorption: Investigating adsorbate and adsorbent properties

NASA Astrophysics Data System (ADS)

Webster, Charles Edwin

1999-12-01

Surface catalyzed reactions play a major role in current chemical production technology. Currently, 90% of all chemicals are produced by heterogeneously catalyzed reactions. Most of these catalyzed reactions involve adsorption, concentrating the substrate(s) (the adsorbate) on the surface of the solid (the adsorbent). Pore volumes, accessible surface areas, and the thermodynamics of adsorption are essential in the understanding of solid surface characteristics fundamental to catalyst and adsorbent screening and selection. Molecular properties such as molecular volumes and projected molecular areas are needed in order to convert moles adsorbed to surface volumes and areas. Generally, these molecular properties have been estimated from bulk properties, but many assumptions are required. As a result, different literature values are employed for these essential molecular properties. Calculated molar volumes and excluded molecular areas are determined and tabulated for a variety of molecules. Molecular dimensions of molecules are important in the understanding of molecular exclusion as well as size and shape selectivity, diffusion, and adsorbent selection. Molecular dimensions can also be used in the determination of the effective catalytic pore size of a catalyst. Adsorption isotherms, on zeolites, (crystalline mineral oxides) and amorphous solids, can be analyzed with the Multiple Equilibrium Analysis (MEA) description of adsorption. The MEA produces equilibrium constants (Ki), capacities (ni), and thermodynamic parameters (enthalpies, ΔHi, and entropies, ΔSi) of adsorption for each process. Pore volumes and accessible surface areas are calculated from the process capacities. Adsorption isotherms can also be predicted for existing and new adsorbate-adsorbent systems with the MEA. The results show that MEA has the potential of becoming a standard characterization method for microporous solids that will lead to an increased understanding of their behavior in gas

Removal of acetaminophen and naproxen by combined coagulation and adsorption using biochar: influence of combined sewer overflow components.

PubMed

Jung, Chanil; Oh, Jeill; Yoon, Yeomin

2015-07-01

The combined coagulation and adsorption of targeted acetaminophen and naproxen using activated biochar and aluminum sulfate were studied under various synthetic "combined sewer overflow" (CSO) conditions. The biochar demonstrated better adsorption performance for both acetaminophen and naproxen (removal, 94.1 and 97.7%, respectively) than that of commercially available powdered activated carbon (removal, 81.6 and 94.1%, respectively) due to superior carbonaceous structure and surface properties examined by nuclear magnetic resonance analysis. The adsorption of naproxen was more favorable, occupying active adsorption sites on the adsorbents by naproxen due to its higher adsorption affinity compared to acetaminophen. Three classified CSO components (i.e., representing hydrophobic organics, hydrophilic organics, and inorganics) played different roles in the adsorption of both adsorbates, resulted in inhibition by humic acid complexation or metal ligands and negative electrostatic repulsion under adsorption and coagulation combined system. Adsorption alone with biochar was determined to be the most effective adsorptive condition for the removal of both acetaminophen and naproxen under various CSO conditions, while both coagulation alone and combined adsorption and coagulation failed to remove the acetaminophen and naproxen adequately due to an increase in ionic strength in the presence of spiked aluminum species derived from the coagulant.

The Preparation of Porous Sol-Gel Silica with Metal Organic Framework MIL-101(Cr) by Microwave-Assisted Hydrothermal Method for Adsorption Chillers.

PubMed

Uma, Kasimayan; Pan, Guan-Ting; Yang, Thomas C-K

2017-06-02

Abst r act: Metal organic framework (MOF) of MIL-101(Cr)-Silica (SiO₂) composites with highly mesoporous and uniform dispersions were synthesized by a microwave-assisted hydrothermal method followed by the sol-gel technique. Water vapor adsorption experiments were conducted on the MIL-101(Cr)-SiO₂ composites for industrial adsorption chiller applications. The effects of MIL-101(Cr)-SiO₂ mixing ratios (ranging from 0% to 52%), the surface area and amount of Lewis and Brønsted sites were comprehensively determined through water vapor adsorption experiments and the adsorption mechanism is also explained. The BET and Langmuir results indicate that the adsorption isotherms associated with the various MIL-101(Cr)-SiO₂ ratios demonstrated Type I and IV adsorption behavior, due to the mesoporous structure of the MIL-101(Cr)-SiO₂. It was observed that the increase in the amount of Lewis and Brønsted sites on the MIL-101(Cr)-SiO₂ composites significantly improves the water vapor adsorption efficiency, for greater stability during the water vapor adsorption experiments.

The Preparation of Porous Sol-Gel Silica with Metal Organic Framework MIL-101(Cr) by Microwave-Assisted Hydrothermal Method for Adsorption Chillers

PubMed Central

Uma, Kasimayan; Pan, Guan-Ting; Yang, Thomas C.-K.

2017-01-01

Metal organic framework (MOF) of MIL-101(Cr)-Silica (SiO2) composites with highly mesoporous and uniform dispersions were synthesized by a microwave-assisted hydrothermal method followed by the sol-gel technique. Water vapor adsorption experiments were conducted on the MIL-101(Cr)-SiO2 composites for industrial adsorption chiller applications. The effects of MIL-101(Cr)-SiO2 mixing ratios (ranging from 0% to 52%), the surface area and amount of Lewis and Brønsted sites were comprehensively determined through water vapor adsorption experiments and the adsorption mechanism is also explained. The BET and Langmuir results indicate that the adsorption isotherms associated with the various MIL-101(Cr)-SiO2 ratios demonstrated Type I and IV adsorption behavior, due to the mesoporous structure of the MIL-101(Cr)-SiO2. It was observed that the increase in the amount of Lewis and Brønsted sites on the MIL-101(Cr)-SiO2 composites significantly improves the water vapor adsorption efficiency, for greater stability during the water vapor adsorption experiments. PMID:28772969

Adsorption effect on the formation of conductive path in defective TiO2: ab initio calculations

NASA Astrophysics Data System (ADS)

Li, Lei; Li, Wenshi; Qin, Han; Yang, Jianfeng; Mao, Ling-Feng

2017-10-01

Although the metal/TiO2/metal junctions providing resistive switching properties have attracted lots of attention in recent decades, revealing the atomic-nature of conductive path in TiO2 active layer remains a critical challenge. Here the effects of metal adsorption on defective TiO2(1 1 0) surface are theoretically investigated via ab initio calculations. The dependence of the conductive path on the adsorption of Ti/Zr/Cu/Pt/O atoms above a lattice Ti-ion in (1 1 0) plane and at 〈1 1 0〉 direction of the defective TiO2(0 0 1) surface are compared. It is found that Ti adsorptions in both sites give larger contributions to the presence of conductive path with more stability and larger transport coefficients at Fermi level, whereas the O adsorptions at both sites fail to produce conductive path. Moreover, the adsorptions of Zr/Cu/Pt atoms reduce the existence possibility of conductive path, especially absorbed above the lattice Ti-ion at 〈1 1 0〉 direction. Thus, it is helpful to clarify the interaction of the metal electrode and oxide layer in resistive random access memory.

Malachite Green Adsorption by Spent Coffee Grounds

NASA Astrophysics Data System (ADS)

Syamimie Atirah Mat, Siti; Zati Hanani Syed Zuber, Sharifah; Rahim, Siti Kartini Enche Ab; Sohaimi, Khairunissa Syairah Ahmad; Halim, Noor Amirah Abdul; Fauziah Zainudin, Nor; Aida Yusoff, Nor; Munirah Rohaizad, Nor; Hidayah Ishak, Noor; Anuar, Adilah; Sarip, Mohd Sharizan Md

2018-03-01

In this work, the ability of spent coffee grounds (SCG) as a low-cost adsorbent to remove malachite green (MG) from aqueous solutions was studied. Batch adsorption tests were carried out to observe the effect of various experimental parameters such as contact time, initial concentration of malachite green and adsorbent dosage on the removal of dye. The results obtained show that the percentage of dye removal will decreased with the increased of initial concentration of dye in the range of 50 mg/L to 250 mg/L. Besides, percentage removal of dye was also found to be increased as the contact time increased until it reached equilibrium condition. The results also showed that the adsorbent dosage in range of 0.2 g to 1.0 g is proportional to the percentage removal of malachite green dye. Study on the kinetic adsorption and isotherm adsorption has also been investigated. The adsorption isotherm data were described by Langmuir isotherm with high-correlation coefficients while the experimental data showed the pseudo-second-order kinetics model was the best model for the adsorption of MG by SCG with the coefficients of correlation R2 > 0.9978.

Adsorption of arsenic(III) into modified lamellar Na-magadiite in aqueous medium-Thermodynamic of adsorption process

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lima Guerra, Denis; Azevedo Pinto, Alane; Airoldi, Claudio

2008-12-15

Synthetic Na-magadiite sample was used for organofunctionalization process with N-propyldiethylenetrimethoxysilane and bis[3-(triethoxysilyl)propyl]tetrasulfide, after expanding the interlayer distance with polar organic solvents such as dimethylsulfoxide (DMSO). The resulted materials were submitted to process of adsorption with arsenic solution at pH 2.0 and 298{+-}1 K. The adsorption isotherms were adjusted using a modified Langmuir equation with regression nonlinear; the net thermal effects obtained from calorimetric titration measurements were adjusted to a modified Langmuir equation. The adsorption process was exothermic ({delta}{sub int}H=-4.15-5.98 kJ mol{sup -1}) accompanied by increase in entropy ({delta}{sub int}S=41.32-62.20 J k{sup -1} mol{sup -1}) and Gibbs energy ({delta}{sub int}G=-22.44-24.56 kJmore » mol{sup -1}). The favorable values corroborate with the arsenic (III)/basic reactive centers interaction at the solid-liquid interface in the spontaneous process. - Grapical Abstract: The results suggest that the adsorption capacities increased with an increase of reactive basic centers in the pendant organic chains of the intercalated agent.« less

Cadmium-109 Radioisotope Adsorption onto Polypyrrole Coated Sawdust of Dryobalanops aromatic: Kinetics and Adsorption Isotherms Modelling

PubMed Central

Olatunji, Michael Adekunle; Khandaker, Mayeen Uddin; Amin, Yusoff Mohd; Mahmud, Habibun Nabi Muhammad Ekramul

2016-01-01

A radiotracer study was conducted to investigate the removal characteristics of cadmium (109Cd) from aqueous solution by polypyrrole/ sawdust composite. Several factors such as solution pH, sorbent dosage, initial concentration, contact time, temperature and interfering metal ions were found to have influence on the adsorption process. The kinetics of adsorption was relatively fast, reaching equilibrium within 3 hours. A lowering of the solution pH reduced the removal efficiency from 99.3 to ~ 46.7% and an ambient temperature of 25°C was found to be optimum for maximum adsorption. The presence of sodium and potassium ions inhibited 109Cd removal from its aqueous solution. The experimental data for 109Cd adsorption showed a very good agreement with the Langmuir isotherm and a pseudo-first order kinetic model. The surface condition of the adsorbent before and after cadmium loading was investigated using BET, FESEM and FTIR. Considering the low cost of the precursor’s materials and the toxicity of 109Cd radioactive metal, polypyrrole synthesized on the sawdust of Dryobalanops aromatic could be used as an efficient adsorbent for the removal of 109Cd radioisotope from radionuclide-containing effluents. PMID:27706232

The Effect of Pluronic 123 Surfactant concentration on The N2 Adsorption Capacity of Mesoporous Silica SBA-15: Dubinin-Astakhov Adsorption Isotherm Analysis

NASA Astrophysics Data System (ADS)

Dhaneswara, Donanta; Siti Agustina, A. A. A.; Dewantoro Adhy, P.; Delayori, Farhan; Fajar Fatriansyah, Jaka

2018-04-01

Mesoporous SBA-15 has been successfully synthesized at various concentration of Pluronic 123 surfactant (7mM, 50 mM, 54 mM, 60 mM and 66 mM) and the effect of these various concentrations on the N2 adsorption capacity has been investigated. The adsorption analysis was conducted using Dubinin-Astakhov isotherm model for multilayer adsorption phenomenon. It was found that etryat low concentration of Pluronic 123, the system exhibits type I adsorption isotherm while at high concentration, the system exhibits type IV adsorption with H1 hysteresis curve which indicates the existence of pores with cylindrical geometry, relatively uniform pore size and possibility of pore network effects. It also was found that, by using D-A isotherm model fitting, at 60 mM concentration of Pluronic 123, SBA-15 has the highest adsorption capacity which stands at 421 cm3/gram.

DFT study on stability and H2 adsorption activity of bimetallic Au79-nPdn (n = 1-55) clusters

NASA Astrophysics Data System (ADS)

Liu, Xuejing; Tian, Dongxu; Meng, Changgong

2013-03-01

The stability and H2 adsorption activity of bimetallic Au79-nPdn (n = 1-55) clusters were studied by density functional theory with GGA-PW91 functional. The stability order for four Pd substitution types is face > mid-edge > corner > edge, and the stability is improved with increasing Pd content. In contrast with the stability order, H2 adsorption activity is corner ≈ edge > mid-edge > face. The Au36Pd43 (3) with Au:Pd ≈ 1:1 ratio and twenty-four Pd substitutions at (1 1 1) facets and nineteen Pd substitutions at subshell sites shows high stability and H2 non-activated dissociation activity. The partial density of d-states and d band center revealed that the electronic properties are closely associated with the geometric characteristic and adsorption activity. Correlating the d band center ɛd and the adsorption energies, the ɛd order agrees with the adsorption activity that the Pd substitution at edge and corner sites are more active than at face and mid-edge sites.

Pentaethylenehexamine-Loaded Hierarchically Porous Silica for CO2 Adsorption

PubMed Central

Ji, Changchun; Huang, Xin; Li, Lei; Xiao, Fukui; Zhao, Ning; Wei, Wei

2016-01-01

Recently, amine-functionalized materials as a prospective chemical sorbent for post combustion CO2 capture have gained great interest. However, the amine grafting for the traditional MCM-41, SBA-15, pore-expanded MCM-41 or SBA-15 supports can cause the pore volume and specific surface area of sorbents to decrease, significantly affecting the CO2 adsorption-desorption dynamics. To overcome this issue, hierarchical porous silica with interparticle macropores and long-range ordering mesopores was prepared and impregnated with pentaethylenehexamine. The pore structure and amino functional group content of the modified silicas were analyzed by scanning electron microscope, transmission electron microscope, N2 adsorption, X-ray powder diffraction, and Fourier transform infrared spectra. Moreover, the effects of the pore structure as well as the amount of PEHA loading of the samples on the CO2 adsorption capacity were investigated in a fixed-bed adsorption system. The CO2 adsorption capacity reached 4.5 mmol CO2/(g of adsorbent) for HPS−PEHA-70 at 75 °C. Further, the adsorption capacity for HPS-PEHA-70 was steady after a total of 15 adsorption-desorption cycles. PMID:28773956

Transport of chromium and selenium in a pristine sand and gravel aquifer: Role of adsorption processes

USGS Publications Warehouse

Kent, D.B.; Davis, J.A.; Anderson, L.C.D.; Rea, B.A.

1995-01-01

Field transport experiments were conducted in an oxic sand and gravel aquifer using Br (bromide ion), Cr (chromium, injected as Cr(VI)), Se (selenium, injected as Se(VI)), and other tracers. The aquifer has mildly acidic pH values and low concentrations of dissolved salts. Within analytical errors, all mobile Cr was present as Cr(VI). All mobile Se was probably present as Se(VI). Adsorption of Cr and Se onto aquifer sediments caused retardation of both tracers. Breakthrough curves for Cr and Se had extensive tails, which caused large decreases in their maximum concentrations relative to the nonreactive Br tracer after only 2.0 m of transport. A surface complexation model was applied to the results of laboratory studies of Cr(VI) adsorption on aquifer solids from the site based on adsorption onto hydrous ferric oxide. The modeling results suggested that the dominant adsorbents in the aquifer solids have lower affinities for anion adsorption than pure hydrous ferric oxide. The steep rising limbs and extensive tails observed in most of the breakthrough curves are qualitatively consistent with the equilibrium surface complexation model; however, slow rates of adsorption and desorption may have contributed to these features. Variations during transport in the concentrations of Cr, Se, and other anions competing for adsorption sites likely gave rise to variations in the extent of adsorption. Adequate description of the observed retardation of Cr and Se would require a coupled transport-adsorption model that can account for these effects. Companion experiments in the mildly reducing zone of the aquifer (Kent et al., 1994) showed a loss of Cr mass, probably resulting from reduction to Cr(III), and little retardation of mobile Cr and Se during transport; this contrast illustrates the influence of aquifer chemistry on the transport of redox-sensitive solutes.

Adsorption and leaching behaviour of bispyribac-sodium in soils.

PubMed

Singh, Neera; Singh, S B

2015-01-01

Adsorption-desorption of the herbicide bispyribac-sodium was studied in four Indian soil types. Bispyribac-sodium was poorly adsorbed in the four soils and adsorption decreased with an increase in the herbicide concentration in solution. Freundlich adsorption coefficient (Kf) values for bispyribac-sodium ranged between 0.37 and 0.87. Slope (1/n) values varied from 0.2 to 0.31 suggesting that bispyribac-sodium adsorption was highly dependent on its initial concentration in solution. Bispyribac-sodium adsorption showed a positive correlation with soil pH (r = 0.809) and clay content (r = 0.699) while no correlation was observed with the organic carbon (r = 0.063) content. Sorbed herbicide was completely desorbed during a single desorption step suggesting that the herbicide was bound by weak adsorptive forces. Leaching studies of herbicide in soil 1 packed column indicated complete loss of soil applied herbicide under a simulated rainfall equivalent to 162 mm.

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.

Adsorption of Dyes in Studying the Surface Chemistry of Ultradispersed Diamond

NASA Astrophysics Data System (ADS)

Khokhlova, T. D.; Yunusova, G. R.; Lanin, S. N.

2018-05-01

The effect the surface chemistry of ultradispersed diamond (UDD) has on the adsorption of watersoluble dyes is considered. A comparison is made to adsorption on graphitized thermal carbon black (GTCB), which has a homogeneous and nonporous surface. The adsorption isotherms of dyes and the dependence of the adsorption on the pH of solutions are measured. It is found that UDD adsorbs acid (anionic) dyes—acid orange (AO) and acid anthraquinone blue (AAB)—but barely adsorbs a basic (cationic) dye, methylene blue (MB), because of the predominance of positively charged basic groups on the surface of UDD. The maximum adsorption of AO is much lower on UDD than on GTCB, while the maximum adsorption of AAB is similar for both surfaces. The adsorption of AO on UDD depends strongly on the pH of the solution, while the adsorption of AAB is independent of this parameter. It is suggested that the adsorption of AAB is determined not only by ionic and hydrophobic interactions but also by coordination interactions with impurity metal ions on a UDD surface. It is concluded that the adsorption of dyes characterizes the chemistry of a UDD surface with high sensitivity.

Adsorption of different amphiphilic molecules onto polystyrene latices.

PubMed

Jódar-Reyes, A B; Ortega-Vinuesa, J L; Martín-Rodríguez, A

2005-02-15

In order to know the influence of the surface characteristics and the chain properties on the adsorption of amphiphilic molecules onto polystyrene latex, a set of experiments to study the adsorption of ionic surfactants, nonionic surfactants and an amphiphilic synthetic peptide on different latex dispersions was performed. The adsorbed amount versus the equilibrium surfactant concentration was determined. The main adsorption mechanism was the hydrophobic attraction between the nonpolar tail of the molecule and the hydrophobic regions of the latex surface. This attraction overcame the electrostatic repulsion between chains and latex surface with identical charge sign. However, the electrostatic interactions chain-surface and chain-chain also played a role. General patterns for the adsorption of ionic chains on charged latex surfaces could be established. Regarding the shape, the isotherms presented different plateaus corresponding to electrostatic effects and conformational changes. The surfactant size also affects the adsorption results: the higher the hydrophilic moiety in the surfactant molecule the lower the adsorbed amount.

Mathematical modelling of cyclic pressure swing adsorption processes

NASA Astrophysics Data System (ADS)

Skvortsov, S. A.; Akulinin, E. I.; Golubyatnikov, O. O.; Dvoretsky, D. S.; Dvoretsky, S. I.

2018-05-01

The paper discusses the results of a numerical analysis of the properties and regimes of the adsorption air separation and oxygen concentration process with a purity of ∼ 40-60%, carried out in a 2-adsorption vacuum-pressure plant with a granular zeolite adsorbent 13X with a productivity of 1.6 · 10-5 m3/s. Computational experiments were carried out using the developed mathematical model and the influence of temperature, pressure, reflux ratio, the duration of the adsorption and desorption stages, the harmonic fluctuations of the inlet pressure during the adsorption stage and the outlet pressure during the desorption stage on the kinetics, and the efficiency of the air separation process by the PSA method were investigated. It is established that the specially organized harmonic fluctuations of the inlet pressure at the stage of adsorption and outlet pressure during the desorption stage lead to an increase in the purity of product oxygen by 4% (vol.).

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. Copyright 2003 Elsevier Science B.V.

Real-Time Monitoring of Azo Dye Interfacial Adsorption at Silica-Water Interface by Total Internal Reflection-Induced Surface Evanescent Wave.

PubMed

Xiong, Yan; Wang, Qing; Duan, Ming; Tan, Jun; Fang, Shenwen; Wu, Jiayi

2018-06-19

An interface research method based on total internal reflection induced evanescent wave (TIR-EW) is developed to monitor the adsorption behavior of azo dye at the silica-water interface. The monitoring system is constructed by employing silica optical fiber (SOF) as both charged substrate for dye adsorption and light transmission waveguide for evanescent wave production. According to the change of evanescent wave intensity and followed by Beer's law, the methylene blue (MB) adsorption behavior can be real-time monitored at the silica-water interface. Langmuir adsorption model and pseudo-first-order model are applied to obtain the related thermodynamic and kinetic data. The adsorption equilibrium constant ( K ads ) and adsorption free energy (Δ G) of MB at the silica-water interface are determined to be (3.3 ± 0.5) × 10 4 M -1 and -25.7 ± 1.7 kJ mol -1 . Meanwhile, this method is highlighted to isolate elementary processes of adsorption and desorption under steady-state conditions, and gives adsorption rate constant ( k a ) and desorption rate constant ( k d ) of 8585 ± 19.8 min -1 and 0.26 ± 0.0006 min -1 for 15 r/min flow rate. The surface interaction process is revealed and adsorption mechanism is proposed, indicating MB first adsorbed on Si-O - sites through electrostatic attraction and then on Si-OH sites through hydrogen bond with increasing MB concentrations. Our findings from this study provided molecular-level interpretation of azo dye adsorption at silica-water interface, and the results provide important insight into how MB adsorption can be controlled at the interface.

A review of functionalized carbon nanotubes and graphene for heavy metal adsorption from water: Preparation, application, and mechanism.

PubMed

Xu, Jiang; Cao, Zhen; Zhang, Yilin; Yuan, Zilin; Lou, Zimo; Xu, Xinhua; Wang, Xiangke

2018-03-01

Carbon-based nanomaterials, especially carbon nanotubes and graphene, have drawn wide attention in recent years as novel materials for environmental applications. Notably, the functionalized derivatives of carbon nanotubes and graphene with high surface area and adsorption sites are proposed to remove heavy metals via adsorption, addressing the pressing pollution of heavy metal. This critical revies assesses the recent development of various functionalized carbon nanotubes and graphene that are used to remove heavy metals from contaminated water, including the preparation and characterization methods of functionalized carbon nanotubes and graphene, their applications for heavy metal adsorption, effects of water chemistry on the adsorption capacity, and decontamination mechanism. Future research directions have also been proposed with the goal of further improving their adsorption performance, the feasibility of industrial applications, and better simulating adsorption mechanisms. Copyright © 2017 Elsevier Ltd. All rights reserved.

Adsorption of selected volatile organic vapors on multiwall carbon nanotubes.

PubMed

Shih, Yang-hsin; Li, Mei-syue

2008-06-15

Carbon nanotubes are expected to play an important role in sensing, pollution treatment and separation techniques. This study examines the adsorption behaviors of volatile organic compounds (VOCs), n-hexane, benzene, trichloroethylene and acetone on two multiwall carbon nanotubes (MWCNTs), CNT1 and CNT2. Among these VOCs, acetone exhibits the highest adsorption capacity. The highest adsorption enthalpies and desorption energies of acetone were also observed. The strong chemical interactions between acetone and both MWCNTs may be the result from chemisorption on the topological defects. The adsorption heats of trichloroethylene, benzene, and n-hexane are indicative of physisorption on the surfaces of both MWCNTs. CNT2 presents a higher adsorption capacity than CNT1 due to the existence of an exterior amorphous carbon layer on CNT2. The amorphous carbon enhances the adsorption capacity of organic chemicals on carbon nanotubes. The morphological and structure order of carbon nanotubes are the primary affects on the adsorption process of organic chemicals.

Off-Gas Adsorption Model Capabilities and Recommendations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lyon, Kevin L.; Welty, Amy K.; Law, Jack

2016-03-01

Off-gas treatment is required to reduce emissions from aqueous fuel reprocessing. Evaluating the products of innovative gas adsorption research requires increased computational simulation capability to more effectively transition from fundamental research to operational design. Early modeling efforts produced the Off-Gas SeParation and REcoverY (OSPREY) model that, while efficient in terms of computation time, was of limited value for complex systems. However, the computational and programming lessons learned in development of the initial model were used to develop Discontinuous Galerkin OSPREY (DGOSPREY), a more effective model. Initial comparisons between OSPREY and DGOSPREY show that, while OSPREY does reasonably well to capturemore » the initial breakthrough time, it displays far too much numerical dispersion to accurately capture the real shape of the breakthrough curves. DGOSPREY is a much better tool as it utilizes a more stable set of numerical methods. In addition, DGOSPREY has shown the capability to capture complex, multispecies adsorption behavior, while OSPREY currently only works for a single adsorbing species. This capability makes DGOSPREY ultimately a more practical tool for real world simulations involving many different gas species. While DGOSPREY has initially performed very well, there is still need for improvement. The current state of DGOSPREY does not include any micro-scale adsorption kinetics and therefore assumes instantaneous adsorption. This is a major source of error in predicting water vapor breakthrough because the kinetics of that adsorption mechanism is particularly slow. However, this deficiency can be remedied by building kinetic kernels into DGOSPREY. Another source of error in DGOSPREY stems from data gaps in single species, such as Kr and Xe, isotherms. Since isotherm data for each gas is currently available at a single temperature, the model is unable to predict adsorption at temperatures outside of the set of data

Adsorption characteristics of (-)-epigallocatechin gallate and caffeine in the extract of waste tea on macroporous adsorption resins functionalized with chloromethyl, amino, and phenylamino groups.

PubMed

Liu, Yongfeng; Bai, Qingqing; Lou, Song; Di, Duolong; Li, Jintian; Guo, Mei

2012-02-15

According to the Friedel-Crafts and amination reaction, a series of macroporous adsorption resins (MARs) with novel structures were synthesized and identified by the Brunauer-Emmett-Teller (BET) method and Fourier transform infrared (FTIR) spectra, and corresponding adsorption behaviors for (-)-epigallocatechin gallate (EGCG) and caffeine (CAF) extracted from waste tea were systemically investigated. Based on evaluation of adsorption kinetics, the kinetic data were well fitted by pseudo-second-order kinetics. Langmuir, Freundlich, Temkin-Pyzhev, and Dubinin-Radushkevich isotherms were selected to illustrate the adsorption process of EGCG and CAF on the MARs. Thermodynamic parameters were adopted to explain in-depth information of inherent energetic changes associated with the adsorption process. The effect of temperature on EGCG and CAF adsorption by D101-3 was further expounded. Van der Waals force, hydrogen bonding, and electrostatic interaction were the main driving forces for the adsorption of EGCG and CAF on the MARs. This study might provide a scientific reference point to aid the industrial large-scale separation and enrichment of EGCG from the extracts of waste tea using modified MARs.

Adsorption of 1-naphthyl methyl carbamate in water by utilizing a surface molecularly imprinted polymer

NASA Astrophysics Data System (ADS)