Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “ADSORPTION”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2Linked to original sources
PubMed1996

Divalent cations modify adsorption of 5'-AMP onto precipitated calcium phosphate: a model for cation modulation of adsorptive processes in primitive aqueous environments.

The adsorption of 5'-AMP onto precipitated calcium phosphate (CaPi) requires the presence of soluble calcium and this dependence exhibits a Michaelian-like behavior. This result suggests that the formation of a complex between 5'-AMP and free Ca2+ (CaAMP) is a prelude to the adsorption of the nucleotide in the solid matrix. At concentrations one order of magnitude higher, Mn2+ and Mg2+ can substitute for soluble Ca2+ in the adsorption of 5'-AMP onto solid CaPi. However, when added simultaneously with 5'-AMP to a heterogeneous mixture that contains CaPi and soluble Ca2+, Mn2+ and Mg2+ inhibit the adsorption of 5'-AMP in a concentration-dependent manner. This suggests the formation of complexes that are much less effective for 5'-AMP adsorption than the CaAMP complex. On the other hand, Mn2+ and Mg2+ cannot promote desorption of the nucleotide attached to the precipitate in the presence of soluble Ca2+ if they are added after adsorption has attained equilibrium. Although desorption of 5'-AMP can be obtained by a sequential dilution of the soluble phase with buffer and no nucleotide in a process that obeys a Langmuir equation, the lack of effect of Mn2+ or Mg2+ when adsorption has attained its maximal value suggests strong interactions between the CaAMP complex and the solid matrix when adsorption equilibrium is reached. The divalent cations present in the matrix also participate with different selectivity in the attachment of the CaAMP complex, indicating that a cation-exchange mechanism could have acted in the modulation of adsorptive/desorptive processes involving biomonomers and phosphate surfaces in primitive aqueous environments.

Adenosine Monophosphate↗
PubMed2006

Protein concentration and adsorption time effects on fibrinogen adsorption at heparinized silica interfaces.

Heparin was modified with adipic dihydrazide and covalently linked to surface-activated silica wafers. X-ray photoelectron spectroscopy was used at each stage of derivatization and showed that successful immobilization had taken place. Surfaces were imaged with atomic force microscopy to determine the uniformity of the heparin layer as well as its thickness. In situ ellipsometry was used to estimate layer thickness as well, and to study protein concentration and adsorption time effects on the adsorption and elution kinetics exhibited by human plasma fibrinogen. The adsorbed amount of fibrinogen increased with time and concentration on each type of surface. Under all experimental conditions, fibrinogen adsorbed at a lower rate and to a lower extent on heparinized as compared to unheparinized silica. In addition, buffer elution experiments showed that fibrinogen was less tightly bound to heparinized silica. In order to examine behavior relative to fibrinogen mobility at these interfaces, the sequential adsorption of fibrinogen was recorded. The difference in adsorption rates between the first and second adsorption cycles, evaluated at identical mass density, indicated that post-adsorptive molecular rearrangements had taken place. In general, higher solution concentration and longer adsorption time in the first adsorption step led to more rearrangement, and these history dependent effects were more pronounced on the heparinized silica. These rearrangements are suggested to involve clustering of adsorbed fibrinogen, in this way increasing the amount of unoccupied area at the interface. These rearrangements were presumably facilitated on the heparinized silica by enhanced lateral mobility of fibrinogen at this negatively charged, highly hydrophilic interface.

Adipates↗
PubMed2004

Adsorption of zinc on bed sediment of River Hindon: adsorption models and kinetics.

The paper presents a study of zinc adsorption using the experimental data on bed sediments of River Hindon in western Uttar Pradesh (India). The effect of various operating variables, viz., initial concentration, solution pH, sediment dose, contact time, and particle size, have been studied. The optimum contact time needed to reach equilibrium was of the order of 60 min and was independent of initial concentration of zinc ions. The extent of adsorption increased with an increase of pH. Furthermore the adsorption of zinc increases with increasing adsorbent doses and decreases with the adsorbent particle size. The content of iron, manganese and organic matter in various fraction of sediment decreases with increasing particle size indicating the possibility of the two geochemical phases to act as the active support material for the adsorption of zinc ions. The adsorption data follows both Langmuir and Freundlich adsorption models. Isotherms were used to determine thermodynamic parameters, viz., free energy change, enthalpy change and entropy change. The negative values of free energy change indicate spontaneous nature of the adsorption while positive values of enthalpy change suggest the endothermic nature of the adsorption of zinc on bed sediment of the River Hindon. The positive values of entropy change indicate randomness at the solid/solution interface.

Adsorption↗
PubMed1991

[Adsorption of pesticides on synthetic adsorption polymers].

On the basis of adsorption of selected pesticides on synthetic adsorption polymers it has been shown that both the adsorption balances as well as kinetics and dynamics of the adsorption strongly depend on the concentration of hydrogen ions of the liquid phase. The dependence of adsorption isotherms on pH value was demonstrated with sufficient accuracy by resorting to the models having been suggested on the ground of IAS theory and the potential one. The kinetic investigations have revealed that the surface diffusion proceeds extremely rapidly in pH ranges that lodge between sorptive pK value and the isoelectric point of the adsorbent surface. The known solutions of transportation and balance equations, which in this case were transferred on the pH-dependent adsorption processes, were implemented for simulating the breakthrough curves. The investigation, covering the effect of the presence of heavy metals in a solution exerted on the pesticides adsorption properties, has shown that the formation of model-pesticide type connections improves the adsorption properties of pesticides to a lesser or greater extent.

2,4-Dichlorophenoxyacetic Acid↗
PubMed2004

Adsorption of gases and vapors on nanoporous Ni2(4,4'-Bipyridine)3(NO3)4 metal-organic framework materials templated with methanol and ethanol: structural effects in adsorption kinetics.

Desolvation of Ni(2)(4,4'-bipyridine)(3)(NO(3))(4).2CH(3)OH and Ni(2)(4,4'-bipyridine)(3)(NO(3))(4).2C(2)H(5)OH give flexible metal-organic porous structures M and E, respectively, which have the same stoichiometry, but subtly different structures. This study combines measurements of the thermodynamics and kinetics of carbon dioxide, methanol, and ethanol sorption on adsorbents M and E over a range of temperatures with adsorbent structural characterization at different adsorbate (guest) loadings. The adsorption kinetics for methanol and ethanol adsorption on porous structure E obey a linear driving force (LDF) mass transfer model for adsorption at low surface coverage. The corresponding adsorption kinetics for porous structure M follow a double exponential (DE) model, which is consistent with two different barriers for diffusion through the windows and along the pores in the structure. The former is a high-energy barrier due to the opening of the windows in the structure, required to allow adsorption to occur, while the latter is a lower-energy barrier for diffusion in the pore cavities. X-ray diffraction studies at various methanol and ethanol loadings showed that the host porous structures E and M underwent different scissoring motions, leading to an increase in unit cell volume with the space group remaining unchanged during adsorption. The results are discussed in terms of reversible adsorbate/adsorbent (host/guest) structural changes and the adsorption mechanism involving hydrogen-bonding interactions with specific surface sites for methanol and ethanol adsorption in relation to pore size and extent of filling. This paper contains the first evidence for individual kinetic barriers to diffusion through windows and pore cavities in flexible porous coordination polymer frameworks.

Journal Article↗
PubMed2006

Coverage-dependent kinetics and thermodynamics of carbon monoxide adsorption on a ternary copper catalyst derived from static adsorption microcalorimetry.

A reliable method for adsorption systems in equilibrium is established to derive coverage-dependent kinetics and thermodynamics from the volumetric data obtained during the static microcalorimetric measurement of heats of adsorption. The Wigner-Polanyi equation is applied to analyze the pressure change as a function of time during stepwise dosing of the adsorptive until thermodynamic adsorption-desorption equilibrium is established. For carbon monoxide adsorption on a hydrogen-reduced Cu/ZnO/Al2O3 catalyst, the adsorption rate constant (ka) is found to be in the range from 10(-6) to 10(-4) Pa(-1) s(-1), and the desorption rate constant (kd) from 10(-4) to 10(-2) s(-1), both increasing with fractional coverage theta. The kinetically derived equilibrium constant Ktheta is in good agreement with Ktheta obtained from the adsorption isotherm. RT ln(Kp0) and the differential heat of adsorption (qdiff) were found to decrease in parallel, reflecting a normal Temkin-type heterogeneity.

Journal Article↗
PubMed1984

Adsorption of pepsin by aluminum hydroxide I: Adsorption mechanism.

Adsorption of pepsin by gibbsite and boehmite, non-acid-reactive forms of aluminum hydroxide, was observed and related to the surface area of the adsorbent. Adsorption was pH dependent, with maximum adsorption occurring between pH 2.7-3.3 for gibbsite and pH 2.7-4.3 for boehmite. Electrostatic attraction was an important adsorption mechanism at the pH conditions encountered in the GI tract; the isoelectric point of pepsin was approximately 1, giving it a negative charge, and the point of zero charge for the adsorbents was greater than 9, giving them a positive charge. However, the pH-adsorption profile can not be fully explained by electrostatic considerations. Desorption studies indicate the importance of specific adsorption because pepsin was not desorbed by washing with acidified water, but was partly desorbed by exchange with phosphate. The IR spectrum of adsorbed pepsin also suggested that specific adsorption of pepsin occurred through anionic ligand exchange involving carboxylate groups of pepsin and surface aluminum ions.

Adsorption↗
PubMed2006

Volumetric interpretation of protein adsorption: Partition coefficients, interphase volumes, and free energies of adsorption to hydrophobic surfaces.

The solution-depletion method of measuring protein adsorption is implemented using SDS gel electrophoresis as a separation and quantification tool. Experimental method is demonstrated using lysozyme (15kDa), alpha-amylase (51kDa), human serum albumin (66kDa), prothrombin (72kDa), immunoglobulin G (160kDa), and fibrinogen (341kDa) adsorption from aqueous-buffer solution to hydrophobic octyl-sepharose and silanized-glass particles. Interpretive mass-balance equations are derived from a model premised on the idea that protein reversibly partitions from bulk solution into a three-dimensional (3D) interphase volume separating the physical-adsorbent surface from bulk solution. Theory both anticipated and accommodated adsorption of all proteins to the two test surfaces, suggesting that the underlying model is descriptive of the essential physical chemistry of protein adsorption. Application of mass balance equations to experimental data quantify partition coefficients P, interphase volumes V(I), and the number of hypothetical layers M occupied by protein adsorbed within V(I). Partition coefficients quantify protein-adsorption avidity through the equilibrium ratio of interphase and bulk-solution-phase w/v (mg/mL) concentrations W(I) and W(B), respectively, such that P identical withW(I)/W(B). Proteins are found to be weak biosurfactants with 45<P<520 and commensurately low apparent free-energy-of-adsorption -6RT<(DeltaG(adsphobic)(0)=-RTlnP)<-4RT. These measurements corroborate independent estimates obtained from interfacial energetics of adsorption (tensiometry) and are in agreement with thermochemical measurements for related proteins by hydrophobic-interaction chromatography. Proteins with molecular weight MW<100kDa occupy a single layer at surface saturation whereas the larger proteins IgG and fibrinogen required two layers.

Adsorption↗
PubMed2004

Adsorption characteristics of Ni(II) on gamma-type alumina particles and its determination of overall adsorption rate by a differential bed reactor.

The adsorption experiment of nickel ion [Ni(II)] on gamma-type alumina by a differential bed reactor in aqueous solutions was investigated to determine the adsorption characteristics and overall adsorption rate. The adsorbed amount increased rapidly with pH from pH 2 to 6 and kept constant over pH 6. The adsorbed amount of Ni(II) increased with temperature from 20 to 50 degrees C. Correlation coefficients (R2) of Langmuir and Freundlich adsorption isotherms were 0.9268 and 0.9489, respectively, and Freundlich isotherm was more suitable for adsorption on gamma-type alumina than Langmuir isotherm. The overall adsorption rate of Ni(II) on gamma-type alumina at pH 6 by a differential bed rector was determined as follows: r = 68.77Ce(1.61) - 17.60qe(0.36). Al(III) ions in solutions were away from the alumina surface during the adsorption of Ni(II) and Al(III) concentration increased with an increasing Ni(II) adsorbed amount on alumina.

Adsorption↗
PubMed2005

Interfacial adsorption of insulin conformational changes and reversibility of adsorption.

The adsorption of human insulin to Teflon particles was studied with respect to conformational changes and the reversibility of adsorption was examined by total internal reflection fluorescence (TIRF). Adsorption isotherms for the adsorption of human insulin indicated high affinity adsorption, even at electrostatic repulsive conditions. The plateau value for adsorption was in accordance with a protein layer consisting primarily of insulin monomers. Conformational changes of the insulin upon adsorption, was investigated by circular dicroism (CD) and fluorescence spectroscopy. The results suggested unfolding of adsorbed insulin, as observed by a decrease in alpha-helix and increase in random coil conformation. The changes in protein structure was not only related to the adsorbed species being monomeric, since CD and fluorescence results were different for adsorbed insulin compared to a monomeric analog of human insulin. Furthermore, the thermal stability in the adsorbed state was changed compared to insulin in solution. On the basis of the TIRF studies with FITC-labelled insulin it was not possible to firmly conclude whether exchange between human insulin in the adsorbed state and in solution takes place, due to the limited time range investigated. However, the desorption mechanism appeared to be different with unlabelled insulin in the bulk solution compared to phosphate buffer.

Adsorption↗
PubMed2005

Separating surface and solvent effects and the notion of critical adsorption energy in the adsorption of phenolic compounds by activated carbons.

A modified form of the Freundlich equation in which the solute equilibrium concentration is normalized with respect to the solute solubility is analyzed and applied to adsorption isotherms of phenol, 4-nitrophenol, 4-chlorophenol, and 2-chlorophenol at different values of pH on commercial activated carbon before and after oxidation. The analysis confirms the importance of normalizing the solute equilibrium concentration when analyzing the adsorption isotherms, and it is suggested that a parameter, K(F10), obtained by taking 10% solubility as the reference point when applying the Freundlich equation, is probably the best comparative estimate of the relative adsorption capacity of the carbon for different phenolic compounds. In combination with the Freundlich exponent, n(F), estimates of the adsorption capacity at any other reference point can then be obtained. Analysis of the experimental results also indicates a need to distinguish between two regimes of adsorption, characterized by an adsorption energy, E(ads), greater than or less than a critical value, E(ca). When E(ads) > E(ca), the shape of the adsorption isotherm is determined by solute-solid interactions. On the other hand, when E(ads) < E(ca), solute-solution interactions become more important.

Adsorption↗
PubMed1998

Bovine serum albumin adsorption onto immobilized organotrichlorosilane surface: influence of the phase separation on protein adsorption patterns.

Octadecyltrichlorosilane (OTS) and [2-(perfluorooctyl)ethyl]trichlorosilane (FOETS) monolayers and their mixed monolayer were polymerized on a water subphase and subsequently immobilized onto a silicon wafer surface by covalent bonding. Atomic force microscopic (AFM) observation of the mixed (OTS/FOETS) monolayer revealed the formation of a phase-separated structure. Protein-adsorption behavior onto the monolayers was investigated in situ on the basis of an attenuated total reflection Fourier transform infrared (ATR-FT-IR) spectroscopic flow cell method and the morphology of the monolayer surface-adsorbed bovine serum albumin (BSA) was observed by AFM. Protein adsorption behavior observed by ATR-FT-IR flow cell method revealed that the amount of BSA adsorption onto the OTS and FOETS monolayers increased remarkably at an initial experimental stage and attained a steady state within a few minutes at pH 7.5. The amount of steady state adsorption was c. 0.18-0.2 microgcm(-2). AFM observation of the monolayer after exposure to BSA solution suggested that BSA adsorbed in the end-on adsorption state on OTS monolayer and side-on one in the FOETS monolayer, respectively. However, in the case of the mixed (OTS/FOETS) monolayer, ATR-FT-IR flow cell experiment revealed that the amount of steady state adsorption of BSA was suppressed. Also, AFM observation revealed that at pH 7.5, BSA preferentially adsorbed onto the FOETS phase of the mixed (OTS/FOETS) monolayer, which had a higher interfacial free energy against water. On the other hand, BSA adsorbed homogeneously onto the OTS and FOETS phases at the isoelectric point of BSA (pH 4.7). These results indicate that the preferential adsorption of BSA onto the FOETS phase in the mixed (OTS/FOETS) monolayer system is due to: (1) the minimization of the interfacial free energy between a monolayer surface and an aqueous solution; and (2) the electrostatic repulsion between BSA molecules bearing negative charges.

Adsorption↗
PubMed1976

[Studies on the adsorption removal of ammonia gas. 1) Adsorption of ammonia gas on several kinds of activated carbons (author's transl)].

The present study was designed to secure some fundamental informations on the adsorption removal of ammonia gas by the static method. In order to find out the suitable activated carbons for the adsorption removal of ammonia gas, amounts of ammonia gas adsorbed on twelve kinds of activated carbons were measured at 30 degrees C and up to 70,000 ppm of ammonia gas. The relations between the amounts of ammonia gas adsorbed on the activated carbons and the physical properties of them were discussed through the results of specific surface area, pore volume, mean pore radius, scanning electron micrograph, pH, and amount of base. The results were as follows: 1) Among the twelve kinds of activated carbons, the activated carbons No. 2, No. 3, and No. 6 adsorbed larger amount of ammonia gas than the others. 2) Adsorption of ammonia gas on the activated carbons seemed to be mainly physical as judged from the values of heat of adsorption. 3) The adsorption capacity of the used activated carbons can be recovered to the original capacity by some treatment. 4) The period to reach adsorption equilibrium was about 5 minutes. 5) It may be concluded that adsorption of ammonia gas on the activated carbons was decided mainly by the surface properties (pH and amount of base) of the activated carbons rather than their porous structures.

Adsorption↗
PubMed1997

Adsorption Enthalpy and Adsorption Isotherm of Tetradecylpyridinium Bromide on Na-Montmorillonite

The adsorption enthalpy and the adsorption isotherm of tetradecylpyridinium bromide (TPB) onto a Na-montmorillonite suspension and the dilution enthalpy of the TPB solution have been determined at 298.15 K. The dilution process is endothermic and the adsorption process is exothermic. For ion exchange adsorption, the interaction between TP+ and the montmorillonite is much stronger than that between Na+ and the montmorillonite because the cumulative adsorption enthalpy increases dramatically with adsorption amount. For molecular adsorption, however, the interaction between TPB and the clay is much weaker.

Journal Article↗
PubMed1998

Adsorption and Heat of Adsorption onto Polymer Particular Surface by Inverse Gas Chromatography

A theory of nonlinear inverse chromatography for arbitrary adsorption isotherms has been developed. Methods of investigating adsorption isotherms and heat of adsorption based on the analysis of chromatograms for different temperatures are suggested. Simple formulae for calculating of adsorption isotherms and heat of adsorption are derived. The adsorption isotherm and heat of adsorption of pyridine on particular poly(imide)siloxane have been investigated by inverse chromatography. Copyright 1998 Academic Press. Copyright 1998Academic Press

Journal Article↗
PubMed2000

In situ adsorption studies at silica/solution interfaces by attenuated total internal reflection fourier transform infrared spectroscopy: examination of adsorption models in normal-phase liquid chromatography

ATR-FT-IR spectroscopy was employed to the study the adsorption of ethyl acetate and 2-propanol to the surface of thin silica sol-gel films in contact with n-heptane solutions. In situ vibrational spectra of silica-adsorbed species provided information regarding the mechanisms of solute retention and elution in normal-phase chromatography. Previous normal-phase chromatographic studies of ethyl acetate adsorption revealed nonlinear isotherms which were explained by both bilayer and adsorbate delocalization models. Infrared spectra of ethyl acetate at the silica surface versus concentration showed that nonlinear adsorption can be attributed to site heterogeneity, where adsorption to free silanols and surface-adsorbed water can be distinguished. Least-squares modeling of the data produced resolved spectra for the two sites and adsorption equilibrium constants that differed by about an order of magnitude. Adsorption of 2-propanol was best modeled by a single Langmuir isotherm showing no significant difference in adsorption energy for the two sites; 2-propanol was shown to easily displace ethyl acetate from the silica surface. Ethyl acetate could also displace 2-propanol from the silica, and least-squares modeling again revealed two-adsorbed-component spectra for ethyl acetate that were indistinguishable from spectra obtained when ethyl acetate adsorbed directly onto the surface.

Journal Article↗
PubMed2006

Thermodynamic analysis of the temperature dependence of OH adsorption on Pt(111) and Pt(100) electrodes in acidic media in the absence of specific anion adsorption.

The effect of temperature on the voltammetric OH adsorption on Pt(111) and Pt(100) electrodes in perchloric acid media has been studied. From a thermodynamic analysis based on a generalized adsorption isotherm, DeltaG degrees , DeltaH degrees , and DeltaS degrees values for the adsorption of OH have been determined. On Pt(111), the adsorption enthalpy ranges between -265 and -235 kJ mol(-1), becoming less exothermic as the OH coverage increases. These values are in reasonable agreement with experimental data and calculated values for the same reaction in gas phase. The adsorption entropy for OH adsorption on Pt(111) ranges from -200 J mol(-1) K(-1) (low coverage) to -110 J mol(-1) K(-1) (high coverage). On the other hand, the enthalpy and entropy of hydroxyl adsorption on Pt(100) are less sensitive to coverage variations, with values ca. DeltaH degrees = -280 kJ mol(-1) and DeltaS degrees = -180 J mol(-1) K(-1). The different dependence of DeltaS degrees with coverage on both electrode surfaces stresses the important effect of the substrate symmetry on the mobility of adsorbed OH species within the water network directly attached to the metal surface.

Journal Article↗
PubMed2006

Insights into adsorption of uncharged macrocyclic complexes into a Nafion Film: Adsorption characteristics and analysis of tetraphenylporphyrine zinc(II).

Tetraphenylporphine zinc(II) (ZnTPP) was found to be adsorbed from its CH2Cl2 solution into a Nafion (Nf) film. The characteristics of the adsorption of ZnTPP into the Nf film were studied using a visible absorption spectroscopic technique. The initial rate (v0, mol cm(-2) s(-1)) for uptake of ZnTPP was saturated with increasing ZnTPP concentration (c0, M) in the solution. This kinetic profile was analyzed in terms of a Michaelis-Menten model considering preequilibrium of ZnTPP adsorption between the solution and the outer layer of the Nf film, followed by diffusion to an inner bulk region, giving a maximum diffusion reflux of v(max) = (2.2 +/- 0.2) x 10(-13) mol cm(-2) s(-1). This is different from the kinetics for the Nf/phthalocyanine zinc(II) (ZnPc) film, which gives a linear plot of v(0) vs c(0). This can be explained by the relatively slow diffusion of ZnTPP in the film compared to that of ZnPc because of steric factors: ZnTPP contains bulky tetraphenyl moieties attached perpendicular to a porphyrin ring, whereas ZnPc has higher planarity. The isotherm for the adsorption of ZnTPP into the Nf film was analyzed using a Langmuir isotherm equation, yielding an equilibrium constant of (3.6 +/- 1.1) x 10(6) M(-1) and a saturated amount of adsorbed ZnTPP of (1.8 +/- 0.1) x 10(-9) mol cm(-2), suggesting monolayer adsorption of ZnTPP on the hydrophobic polymer network interfacial with hydrophilic transport channels without significant intermolecular overlap. This is in contrast to the multilayer adsorption mode suggested for the ZnPc adsorption. The tetraphenyl moieties could prevent the stacking of ZnTPP for multilayer adsorption.

Journal Article↗