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PubMed1989

In vitro adsorption of bile salts by colestipol hydrochloride.

The acid-base titration of colestipol hydrochloride exhibits no sharp inflection points, indicating a weakly basic anion-exchange copolymer. The swelling of colestipol hydrochloride in water and the adsorption of cholate anion are inversely related to pH and are, therefore, related to the ionization state of the copolymer. The Langmuir adsorption parameters at pH 7.5 and 37 degrees C are similar for cholate, glycocholate, and taurocholate anions. Adsorption capacity was not related to particle size and exceeded the adsorptive capacity of the external surface by three orders of magnitude. Therefore, it is believed that the swelling of colestipol hydrochloride makes extensive internal surface area available for adsorption of bile salts. The rate of adsorption depends on the concentration of sodium cholate to which the colestipol hydrochloride is exposed. Adsorption was complete within 5 min when the concentration was below the adsorptive capacity. In contrast, adsorption at levels of sodium cholate at or above the adsorptive capacity was not complete within a 3-hr test period.

Adsorption↗

PubMed2006

Predicting the adsorption capacity and isotherm curvature of organic compounds onto activated carbons in natural waters.

A simple approach to predict the adsorption capacity and isotherm curvature of organic compounds onto activated carbon in natural water was investigated. A combination of the well-known equivalent background compound (EBC), and the simplified competitive adsorption model (SCAM) was employed to delineate the equilibrium capacity. This SCAM-EBC approach may reduce the numerical and experimental effort to obtain the parameters required to predict the adsorption capacity for a specific adsorption system. Several sets of experimental data, including weakly adsorbing (MTBE), strongly adsorbing compounds (TCP, atrazine, and chloroform), and two taste and odor causing compounds (MIB and geosmin) onto different activated carbons in three natural waters and a synthetic groundwater, were tested to verify the SCAM-EBC approach. Based on the approach, a parameter, called relative adsorptivity, describing the adsorption preference of the adsorbent between EBC and the target compound was employed to simulate the isotherm curvature in natural water. The relative adsorptivity of the SCAM-EBC approach is constant and can be directly obtained from the SCAM-EBC parameters in a specific adsorption system. The potential and extent of isotherm curvature can be simulated by only changing the parameter of relative adsorptivity. The marked isotherm curvature was found while the relative adsorptivity is larger than 2.0 to 4.0 for all the systems tested.

Adsorption↗

PubMed2003

Adsorption mechanism of chloroacetanilide herbicides to modified montmorillonite.

This study was undertaken to characterize the adsorption mechanism of alachlor and metolachlor on montmorillonite modified with cationic surfactants. Adsorbed amounts of cationic surfactant on montmorillonite surfaces were determined by CNHSO analyzer. Equilibrium concentrations of alachlor and metolachlor were determined by GC and adsorption results were fit to a linear regression equation. The slope of the isotherms (Kd) was normalized to the fraction of organic carbon on montmorillonite complexes to produce corresponding Koc. Adsorption of surfactants fit very well to Langmuir equation. Increased basal spacing indicates that surfactant molecules could penetrate through the interlayer spacing and arrange themselves in different ways. Equilibrium data of alachlor and metolachlor suggest that adsorption may occur via physical or chemical bonds. Koc values of alachlor or metolachlor decreased as the fraction of the organic carbon increased in montmorillonite complexes indicating independent adsorption process. Changes of the molar free energy of the adsorption reactions were in the range of physical adsorption, indicating that adsorption reactions are spontaneous and the molecules either adsorb on the surface or penetrate into the inter-layers of montmorillonite-surfactant complex. Careful investigation of the adsorption data suggests that interaction may occur via the active groups such as carbonyl group (-C=O), anilidic (C-N) group and/or phenyl rings. This information may provide better understanding on adsorption mechanism and be useful in designing ecologically acceptable herbicide formulations.

Acetamides↗

PubMed1982

Adsorption of coliphages T1 and T7 to clay minerals.

Coliphages T1 and T7 of Escherichia coli were absorbed by kaolinite (K) and montmorillonite (M). Maximum adsorption of T7 (96%) to M was greater than that of T1 (84%), but the adsorption of both coliphages to K was the same (99%). Positively charged sites (i.e., anion exchange sites) on the clays appeared to be primarily responsible for the adsorption of T1 to K but only partially responsible for the adsorption of T1 to M; equilibrium adsorption isotherms of T1 to K and M did not show a correlation between adsorption and the cation exchange capacity of the clays, and the reduction in adsorption caused by sodium metaphosphate (a polyanion that interacts with positively charged sites on clay) was more pronounced with K than with M. The equilibrium adsorption isotherms of T7 to K and M suggested a correlation between adsorption and the cation exchange capacity of the clays. However, studies with sodium metaphosphate indicated that T7 also adsorbed to positively charged sites on the clays, especially on K. Adsorption of the coliphages to positively charged sites was greater with K than with M, probably because the ratio of positively charged sites to negatively charged sites was greater on K than on M.

Adsorption↗

PubMed1983

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

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

Adsorption↗

PubMed1982

Adsorption of lysozyme from human whole saliva by Streptococcus sanguis 903 and other oral microorganisms.

Several strains of Streptococcus sanguis, Streptococcus mutans, Streptococcus mitis, Actinomyces viscosus, and Actinomyces naeslundii plus fresh isolates of Streptococcus salivarius were surveyed for their abilities to deplete lysozyme from human-whole-saliva supernatant. Bacteria were incubated in saliva for 60 min at 37 degrees C and then removed by centrifugation, and the recovered supernatant solutions were assayed for lysozyme activity by using whole cells of Micrococcus lysodeikticus as the substrate. Mean lysozyme depletions by bacterial strains varied over a wide (eightfold) range. The greatest mean depletion of lysozyme (60 to 70%) was observed with S. sanguis (biotype I), serotype b of S. mutans, and the fresh S. salivarius isolates. The lowest mean depletion was noted with S. mitis (15%) and biotype II S. sanguis (ca. 30%). The remaining species and strains exhibited an intermediate degree of depletion. In studies with S. sanguis 903, lysozyme was depleted by normal or heated (90 degrees C, 30 min) bacteria and could be recovered from the organism. Furthermore, under appropriate conditions, lysozyme depletion by cells at 0 and 37 degrees C was very similar. On the basis of these observations, we concluded that depletion was due to the adsorption of lysozyme by the organism. With S. sanguis 903, lysozyme adsorption depended on the concentration of bacteria, time of incubation, and the ionic strength of the medium. The extent of adsorption, however, was independent of pH's of 3.9 to 8.3. When a low concentration of S. sanguis 903 was used, lysozyme adsorption reached saturation (4 mug of adsorbed lysozyme per 10(7) cells) at 20 mug of lysozyme added per ml. Salivary lysozyme adsorption by several other oral microorganisms (A. viscosus WVU 626 and WVU 627, S. sanguis 73x11, S. mutans BHT, and S. salivarius NG) was similar to that of S. sanguis 903 in sensitivity to ionic strength. Lysozyme adsorption by S. sanguis 903 from either a buffer solution or a saliva supernatant was more sensitive to ionic strength at 0 than at 37 degrees C. On the basis of results from experiments in saliva versus buffer, we concluded that saliva had no major effect on the extent of lysozyme adsorption by S. sanguis 903 other than providing a source of ionic strength. A comparison of pH and ionic strength effects on lysozyme adsorption by S. sanguis 903 with literature reports of lysozyme lysis of whole cells and hydrolysis of cell walls, peptidoglycan, and (GlcNAc)(4) suggested that adsorption by S. sanguis 903 was more dependent on electrostatic interactions than was lysozyme catalysis. The possibility is discussed that anionic bacterial surface components mediate lysozyme adsorption and temper the potential effects of lysozyme on the microorganisms.

Actinomyces↗

PubMed1993

Adsorption behavior of fibrinogen to sulfonated polyethyleneoxide-grafted polyurethane surfaces.

Fibrinogen adsorptions to surface modified polyurethanes (PU, PU-PEO, and PU-PEO-SO3) were studied from plasma in vitro. PU and PU-PEO surfaces demonstrated that initial adsorption increases with increasing plasma concentration in kinetic profiles and adsorption time in adsorption profiles as a function of plasma concentration, but after the plateau is reached, its adsorption amount decreases as plasma concentration (0.2-2.0%) and adsorption time (1-120 min) increase, respectively. In contrast, PU-PEO-SO3 showed that initial adsorption is almost same regardless of plasma concentration and adsorption time, which is due to the high affinity of surface sulfonate group to fibrinogen. All the surfaces indicated the Vroman effect at about 0.6% plasma concentration; however, the displacement was relatively low. Adsorbed amount of fibrinogen at steady state decreased in the order: PU > PU-PEO-SO3 > PU-PEO, regardless of adsorption time and plasma concentration. The adsorption behavior of PU-PEO-SO3 is attributed to both effect of low binding affinity of PEO chain and high affinity of pendant sulfonate group toward fibrinogen.

Adsorption↗

PubMed2006

Adsorption of viruses to soil: impact of anaerobic treatment.

The adsorption of viruses in untreated flushed dairy manure wastewater (FDMW), anaerobically digested flushed dairy manure wastewater (ADFDMW) and groundwater to sandy soil was investigated. Batch adsorption studies showed differential adsorption of viruses in groundwater to soil. Less than 75% of PRD1 and MS2 added to groundwater adsorbed after 1 h, but greater than 95% of phiX174 and poliovirus 1 adsorbed to the soil. Adsorption differences in groundwater were related to the isoelectric points of the viruses. Suspending phages in untreated and treated wastewater reduced adsorption compared with groundwater. For MS2, more phages were adsorbed using ADFDMW than with FDMW. Adsorption of poliovirus 1 was not affected by FDMW and ADFDMW. Small column studies (6 x 2.5 cm) produced a similar trend in that adsorption was observed with groundwater and both FDMW and ADFDMW reduced virus adsorption. Groundwater, FDMW or ADFDMW did not affect the adsorption of poliovirus 1 in column studies. The major difference between FDMW and ADFDMW was in mobilisation of adsorbed viruses. The application of FDMW to soil columns with adsorbed viruses caused significantly more viruses to be mobilised than did the application of rainwater or ADFDMW. These results showed that treating FDMW by anaerobic digestion increased the adsorption of viruses to soil and decreased detachment of adsorbed viruses. As the potential for new zoonotic pathogens becomes known, the treatment of animal wastes may become mandatory. The assessment and management of viruses in manure for addressing possible risk to animal and human health is of interest.

Adsorption↗

PubMed2003

[EXAFS studies on adsorption-desorption mechanism of Zn at the manganite-water interface].

Microscopic structures of Zn(II) surface complexes adsorbed at the manganite(gamma-MnOOH)-water interface were studied using extended X-ray absorption fine structure(EXAFS) spectroscopy. Quantitative analysis of the EXAFS spectra showed that, in a 0.1 mol/L NaNO3 solution of pH 7.5, Zn(II) was adsorbed onto the solid surface by sharing the oxygen atom in the hydrous Zn2+ ions and in the structural unit MnO6 on the manganite surface. Most of the adsorbed Zn(II) was in the form of octahedral Zn(H2O2)(6)2+, but part of Zn(II) was adsorbed as tetrahedral Zn(OH)2 or Zn(OH)(4)2-. The average Zn-O bond length was 1.998 +/- 0.010 A (n = 3). The ZnO polyhedron of the hydrous Zn2+ ions was linked to the octahedron MnO6 of the manganite in two modes by sharing two O atoms on the edges of the polyhedral and/or one O atom on the corners of the polyhedral. EXAFS analysis of the second sphere indicated that Zn (II) adsorbed on the manganite resulted in two Zn-Mn atomic distances of 3.08 +/- 0.024A (n = 3) (R1) and 3.54 +/- 0.018 A (n = 3) (R2), corresponding to the edge-linkage (stronger adsorption site) and corner-linkage (weaker adsorption site), respectively. This result confirmed the basic hypothesis of Metastable Equilibrium Adsorption (MEA) theory from a molecular level that adsorption density gamma (mol/m2) is not a state variable, because adsorption density for the same adsorbate may have different chemical potential values due to different microscopic structure and adsorbate energy status. Macroscopic adsorption-desorption experiments showed that adsorption of Zn(II) onto manganite was largely irreversible (big adsorption hysteresis). EXAFS results indicated that the microscopic mechanism for the adsorption irreversibility was corresponded to the strong adsorption sites of edge sharing linkage between the adsorbate and adsorbent polyhedra.

Adsorption↗

PubMed2005

[Phosphate adsorption and desorption characteristics of several fly ashes].

Through adsorption-desorption experiment and incubation test, this paper studied the phosphate adsorption and desorption characteristics of several fly ashes. The test fly ashes contained 0.545 - 4.540 g x kg(-1) of total P and 19.55 - 163.0 mg x kg(-1) of available P, which were significantly higher than those in soils. The P adsorption capacity of fly ashes increased with increasing added P, while their P adsorption rate was in adverse. Fly ashes had a higher P adsorption rate but a lower P desorption rate than soils, mainly because fly ashes had more P adsorption sites and stronger bound energy. In this study, Langmuir, Freundlich, and Temkin equations were fit to the measured data, and the MBC value in Langmuir equation, a value in Freundlich equation, and k2 value in Temkin equation could be used as a comprehensive index to characterize the potential phosphate adsorptivity of fly ashes. The larger these values were, the stronger the P adsorptivity was. The MBC, a and k2 value of 5 fly ashes collected from different locations was in order of Xiangtan power factory (5 167.7, 4 056.2 and 831.5) > Yueyang paper factory (1 650.7, 2803.4 and 711.9) >Huaneng power factory (303.0, 1677.6 and 368.7) > Zhuzhou power factory (34.7,413.48 and 213.8) > Dongting nitrogen fertilizer factory (34.7, 413.48 and 213.8). The P fixation by fly ashes generally increased with their increasing water content, and their phosphate adsorption was mainly specific adsorption and chemical precipitation, suggesting that the P fixation and the water content of fly ashes should be considered when fly ash was used as soil amendment or as compound fertilizer filling substance.

Adsorption↗

PubMed1970

Evaluation of various substances to prevent adsorption of tuberculin purified protein derivative (PPD) to glass surfaces.

It is well known that a dilute tuberculin PPD solution (1 IU or 5 IU per dose) very rapidly loses its potency owing to adsorption of tuberculoprotein to the wall of the container into which it is dispensed. The amount of tuberculoprotein adsorbed per cm(2) of glass surface has been measured for phosphate-buffered saline over a wide pH range (pH 1 to pH 10). The maximum adsorption was found at pH 4 (0.31 mug/cm(2)) and the least at between pH 6 and pH 10 (0.15 mug/cm(2)). The rate of adsorption of tuberculoprotein to glass was not changed when the phosphate-buffered saline was replaced by borate-buffered saline. Tuberculin PPD prepared by the ammonium sulfate precipitation method, by the trichloroacetic acid precipitation method and by a combination of both methods adsorbed equally well to glass and no difference in the rate of adsorption for these tuberculoproteins was found.Forty-two substances in addition to Tween 80 were tested for their property to prevent adsorption of tuberculoprotein to glass in dilute tuberculin PPD solutions (50 IU/ml of (14)C-labelled PPD). The most efficient anti-adsorption agents were found to be nonionic surfactants, some ionic surfactants and some colloidal substances; polypeptides and non-surface-active substances of low molecular weight showed little or no anti-adsorption property.The labelling of PPD with (14)C has proved to be a valuable tool, particularly for long-term adsorption studies and for screening substances to be used as efficient anti-adsorption agents. These studies have permitted the selection of agents which could be added to dilute solutions of tuberculin PPD (10 IU/ml to 500 IU/ml or 0.2 mug/ml to 10 mug/ml respectively) in order to avoid loss of potency due to adsorption.

Adsorption↗

PubMed1976

The in vitro adsorption of some antibiotics on antacids.

The adsorption of oxytetracycline hydrochloride, tetracycline hydrochloride, doxycycline hyclate, triacetyloleandomycin, chloramphenicol, ampicillin, and cloxacillin sodium was studied on various antacids namely, magnesium trisilicate, magnesium oxide, calcium carbonate, bismuth oxycarbonate, aluminium hydroxide, and kaolin. The adsorption of the various antibiotics by milk was also tested as milk is frequently used as an antacid. Charcoal was included in the present study as a model adsorbent having a large hydrophobic surface. The adsorption of the various antibiotics on the different antacids and other adsorbents in most cases obeyed the Freundlich adsorption isotherm. Magnesium trisilicate and magnesium oxide showed the highest adsorptive capacity, relative to other antacids used, for most antibiotics. Calcium carbonate and aluminium hydroxide and intermediate power while kaolin and bismuth oxycarbonate had the least adsorptive power. Charcoal exhibited a marked adsorption for all antibiotics tested. Tetracyclines were found to be more highly adsorbed than other antibiotics studied. Triacetyloleandomycin and chloramphenicol had intermediate values. Ampicillin was only adsorbed to a slight extent while cloxacillin was not adsorbed on the antacids used. The extent of adsorption was correlated to the structure of both the adsorbent and adsorbate, the pH of the adsorbent suspension, and to the polarity of the antibiotic in such pH. The reversibility of the adsorption process was studied in different media and at pH values similar to those of the gastrointestinal tract. The extent of elution was found to be inversely proportional to the adsorptive capacity of the different adsorbents. In general, 0.0143 n NaHCO3 solution was found to possess higher eluting properties than 0.01 n HCl. An exception to this pattern was observed with tetracyclines adsorbed on aluminium hydroxide where the elution with acid resulted in a higher degree of desorption. Careful in vitro and in vivo testing of drug availability is advisable prior to the concomitant administration of antibiotics with antacids or other adsorbents.

Adsorption↗

PubMedDate not supplied

Role of the electrostatic attractive force in the adsorption of proteins by aluminum hydroxide adjuvant.

The fact that both aluminum hydroxide adjuvant and proteins have a pH dependent surface charge means that electrostatic forces play a role in the adsorption of proteins by aluminum hydroxide adjuvant during the preparation of vaccines. The objective of this study was to examine the contribution of the electrostatic attractive force in the adsorption of proteins by aluminum hydroxide adjuvant. Since the surface charge characteristics of aluminum hydroxide adjuvant can be modified by the adsorption of phosphate anion, a series of aluminum hydroxide adjuvants were prepared by treatment with various concentrations of phosphate anion. The isoelectric points (iep) of these adjuvants ranged from 11.0 to 4.6 and the electrophoretic mobilities at pH 7.4 ranged from 2.0 to -3.3 microns cm/V s. The line broadening of the (020) band of the X-ray diffraction pattern indicated that treatment with phosphate anion did not change the primary crystallite dimension. Adsorption at pH 7.4 of positively charged lysozyme (iep = 11.1) was directly related to the negative surface charge of the adjuvant. No adsorption occurred when the surface charge was positive. In contrast, negatively charged ovalbumin (iep = 4.6) was adsorbed by all of the adjuvants at pH 7.4, although the adsorptive capacity was the greatest when the surface charge was positive. The results indicate that adsorptive forces in addition to the electrostatic attractive force play an important role in the adsorption of some proteins by aluminum hydroxide adjuvant. It is believed the structurally flexible proteins, like ovalbumin, exhibit more complex adsorption behavior than structurally rigid proteins, like lysozyme, for which adsorptive behavior can be explained by electrostatic forces.

Adsorption↗

PubMed1996

Adsorption Behavior of Cationic and Nonionic Surfactant Mixtures at the Alumina-Water Interface.

The solution and interfacial behavior of surfactant mixtures was investigated using a cationic surfactant, tetradecyl trimethyl ammonium chloride (TTAC), and a nonionic surfactant, pentadecylethoxylated nonyl phenol (NP-15), with alumina as the substrate. The cationic TTAC adsorbed at the alumina-water interface as a result of electrostatic attraction at pH approximately 10 whereas the nonionic NP-15 did not. Interestingly, in the mixed surfactant system, the tetradecyl trimethyl ammonium chloride forced adsorption of the NP-15 as a result of hydrophobic interactions between the adsorbed surfactant chains at the alumina-water interface. The adsorption behavior was dependent upon the ratio of the two surfactants in the mixture as well as the order of addition. With an increase in TTAC content, the adsorption density of NP-15 increased and the isotherm shifted to lower surfactant concentrations. The adsorption of TTAC decreased under conditions of saturation adsorption due to the bulkiness of the coadsorbed NP-15 as well as competition for common adsorption sites. However, below saturation adsorption conditions, the adsorption of TTAC was increased due to synergistic interactions between the cationic and nonionic heads leading to reduced repulsion among the cationic headgroups. Zeta potential measurements showed that, with an increase of NP-15 in the mixtures, the positive charge of the TTAC was partially screened by the coadsorbed NP-15. Surface tension of the surfactant mixtures was also measured, and regular solution theory was used to model the interactions between the surfactants. Monomer concentrations obtained using the theory were correlated with the adsorption tendencies and it was seen that TTAC adsorption corresponded with its monomer concentration but that of NP-15 did not, suggesting the need for adequate theories for interactions between surfactants.

Journal Article↗

PubMed1997

Adsorption of Pb(II), NTA, and Pb(II)-NTA onto TiO2

Nitrilotriacetic acid (NTA) is extensively used in different industries because of its excellent chelating properties. Introduction of NTA into the natural environment is a concern because of mobilization of heavy metal species that may be otherwise bound to natural particulate matter. The present study investigates the adsorption behavior of Pb(II) and NTA, both as individual species and as complex species onto titanium dioxide. This adsorption information is important in considering the TiO2-assisted photocatalytic treatment of these metal-organic complexes. Pb(II) shows a typical cationic type of adsorption behavior, whereas NTA demonstrates an anionic type of adsorption trend. Results from stoichiometric ternary systems show a gradual increase in Pb(II) adsorption and a decrease in NTA removal with an increase in pH. However, for the cases of Pb(II) > NTA, increased NTA adsorption as compared to pure NTA systems was noted even at higher pH. Model predictions employing MINTEQA2 software followed the experimental trends. Experimental and model results from ternary systems suggest adsorption of free Pb(II) and NTA, as well as ternary Ti-NTA-Pb(II) and Ti-O-Pb(II)-NTA2- species. The cationic-type complexation, i.e., Ti-O-Pb(II)-NTA2-, was essential for the successful NTA adsorption modeling, especially at higher pH and for Pb > NTA systems, where significant NTA adsorption was noted even at very high pH values. Most of the previous metal-ligand adsorption studies did not consider such a surface complexation. However, the present results indicate that any groundwater transport modeling of such pollutants will require the inclusion of cationic-type surface complexation, in addition to other surface species. Copyright 1997 Academic Press. Copyright 1997Academic Press

Journal Article↗

PubMed1998

The Influence of Temperature on the Adsorption of Cadmium(II) and Cobalt(II) on Kaolinite.

The adsorption of Cd(II) and Co(II) onto kaolinite was investigated at five temperatures between 10 and 70 degreesC. Adsorption edges showed that both Cd(II) and Co(II) adsorbed onto kaolinite in two stages, separated by a plateau between pH 4 and 7. Initial adsorption commenced at about the same pH for both cations, but at each temperature the second-stage adsorption occurred at a slightly lower pH for Co(II) than for Cd(II). At higher temperatures adsorption was generally shifted to lower pH. Adsorption isotherms at pH 5.50 for both cations could be fitted closely by a simple Langmuir model at all temperatures. A two-site Langmuir model provided a substantially better fit for isotherms at pH 7.50 for Cd(II) and pH 7.00 for Co(II). At pH 5.50 the maximum adsorption density estimated from Langmuir modelling was approximately the same (1 µmol m-2) for both cations and at all temperatures. A similar value was found for one of the model sites at pH 7.50 for Cd(II) and at pH 7.00 for Co(II). Potentiometric titrations of kaolinite suspensions, in the presence and absence of added Cd(II) or Co(II), could be modeled accurately by a constant-capacitance surface complexation model. The data for adsorption of both cations could be fitted at all temperatures using a model that assumed ion exchange at permanent charge sites on silanol faces and complexation to hydroxyl edge groups. Thermodynamic parameters estimated from both the Langmuir and surface complexation models showed that adsorption of Cd(II) and Co(II) were endothermic. For the surface complexation model, enthalpies of adsorption on exchange sites were about 10 kJ mol-1, but at the variable-charge sites the enthalpy changes were about 70 kJ mol-1. For all these reactions the entropy changes were positive, with values of the order of 100 J K-1 mol-1. Trends for the Langmuir model were qualitatively similar. Copyright 1998 Academic Press.

Journal Article↗

PubMed1998

Kinetic-Diffusion-Controlled Adsorption and Desorption Kinetics on Planar Surfaces.

The adsorption and desorption kinetics of water-soluble associative polymers with different molecular weights on the silicon wafers were studied by ellipsometry. The parameters characterizing the adsorption and desorption processes such as (a) the maximum amount of adsorbate adsorbed, Gammainfinity, (b) the equilibrium constant, K(p), (c) the activation energy of adsorption, (-DeltaH), (d) the rate constants for adsorption and desorption processes, Kad, Kdes, (e) the coefficient of diffusion, D0, (f) the activation energy of the effective diffusion, Q, and (g) the time needed to attain the equilibrium states for the adsorption and desorption processes were calculated from the experimental ellipsometric data. It is shown that the adsorption kinetics for mixtures over a wide range of concentrations is governed by: (I) the kinetic adsorption at the interface, (II) the kinetic adsorption at the interfaces as well as simultaneous diffusion, and/or (III) diffusion. The existence of regimes (I), (II), and (III) for adsorption and desorption kinetics are justified by using the experimental data for the adsorption and desorption kinetics of water-soluble associative polymers with different molecular weights of 12, 62, and 120 kg/mol. Copyright 1998 Academic Press.

Journal Article↗

PubMed2000

Adsorption of Benzoic and 4-Heptylbenzoic Acid on Different Silica Substrates from Organic and Aqueous Solution.

In studies of the adsorption of surface-active molecules from organic phase on mineral surfaces in relation to wettability alterations, the system has normally been made water-free. However, since water is an inherent part of all oil-bearing formations, it is of interest to study adsorption in solid/water/oil systems. In this paper we therefore study the adsorption of benzoic (BzCOOH) and 4-heptylbenzoic (4-HBA) acid from organic solution on different silica substrates in the presence of water. The results show that the adsorption is enhanced in the presence of water and that 4-HBA has a higher affinity for the silica surface than does BzCOOH. Variations in the surface properties of the silica substrates had no significant effect on the adsorption. In studies of the adsorption of organic acids from aqueous phase, the acid has been added either as the corresponding acid salt or as the acid itself. However, the adsorption behavior of the acid salt is not necessarily representative of the adsorption behavior of the acid. To investigate this more closely, we studied the adsorption of benzoic acid added to water both as sodium benzoate (BzCOO(-)Na(+)) and as BzCOOH. The results revealed a significant increase in the maximum adsorption when BzCOO(-)Na(+) was used as adsorbate instead of BzCOOH. Copyright 2000 Academic Press.

Journal Article↗