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PubMed2004

Competitive adsorption of aqueous metal ions on an oxidized nanoporous activated carbon.

Competitive adsorption is the usual situation in real applications, and it is of critical importance in determining the overall performance of an adsorbent. In this study, the competitive adsorption characteristics of all the combinations of binary mixtures of aqueous metal ion species Ca2+(aq), Cd2+(aq), Pb2+(aq), and Hg2+(aq) on a functionalized activated carbon were investigated. The porous structure of the functionalized active carbon was characterized using N2 (77 K) and CO2 (273 K) adsorption. The surface group characteristics were examined by temperature-programmed desorption, Fourier transform infrared spectroscopy, Raman spectroscopy, acid/base titrations, and measurement of the point of zero charge (pHpzc). The adsorption of aqueous metal ion species, M2+(aq), on acidic oxygen functional group sites mainly involves an ion exchange mechanism. The ratios of protons displaced to the amount of M2+(aq) metal species adsorbed have a linear relationship for both single-ion and binary mixtures of these species. Hydrolysis of metal species in solution may affect the adsorption, and this is the case for adsorption of Hg2+(aq) and Pb2+(aq). Competitive adsorption decreases the amounts of individual metal ions adsorbed, but the maximum amounts adsorbed still follow the order Hg2+(aq) > Pb2+(aq) > Cd2+(aq) > Ca2+(aq) obtained for single metal ion adsorption. The adsorption isotherms for single metal ion species were used to develop a model for competitive adsorption in binary mixtures, involving exchange of ions in solution with surface proton sites and adsorbed metal ions, with the species having different accessibilities to the porous structure. The model was validated against the experimental data.

Journal Article↗
PubMed2004

Adsorption and vibrational spectroscopy of ammonia at mordenite: ab initio study.

The adsorption of ammonia at various active centers at the outer and inner surfaces of mordenite, involving Brønsted acid (BA) sites, terminal silanol groups, and Lewis sites has been investigated using periodic ab initio density-functional theory. It is shown that ammonia forms an ammonium ion when adsorbed at strong BA sites. The calculated adsorption energies for different BA sites vary in the interval from 111.5 to 174.7 kJ/mol depending on the local environment of the adduct. The lowest adsorption energy is found for a monodentate complex in the main channel, the highest for a tetradentate configuration in the side pocket. At weak BA sites such as terminal silanol groups or a defect with a BA site in a two-membered ring ammonia is H bonded via the N atom. Additional weak H bonds are formed between H atoms of ammonia and O atoms of neighboring terminal silanol groups. The calculated adsorption energies for such adducts range between 61.7 and 70.9 kJ/mol. The interaction of ammonia with different Lewis sites is shown to range between weak (DeltaE(ads)=17.8 kJ/mol) and very strong (DeltaE(ads)=161.7 kJ/mol), the strongest Lewis site being a tricoordinated Al atom at the outer surface. Our results are in very good agreement with the distribution of desorption energies estimated from temperature-programmed desorption (TPD) and microcalorimetry experiments, the multipeaked structure of the TPD spectra is shown to arise from strong and weak Brønsted and Lewis sites. The vibrational properties of the adsorption complexes are investigated using a force-constant approach. The stretching and bending modes of NH(4) (+) adsorbed to the zeolite are strongly influenced by the local environment. The strongest redshift is calculated for the asymmetric stretching mode involving the NH group hydrogen bonded to the bridging O atom of the BA site, the shift is largest for a monodentate and smallest for a tetradentate adsorption complex. The reduced symmetry of the adsorbate also leads to a substantial splitting of the stretching and bending modes. In agreement with experiment we show that the main vibrational feature which differentiates coordinatively bonded ammonia from a hydrogen-bonded ammonium ion is the absence of bending modes above 1630 cm(-1) and in the region between 1260 and 1600 cm(-1), and a low-frequency bending band in the range from 1130 to 1260 cm(-1). The calculated distribution of vibrational frequencies agrees very well with the measured infrared adsorption spectra. From the comparison of the adsorption data and the vibrational spectra we conclude that due to the complex adsorption geometry the redshift of the asymmetric stretching is a better measure of the acidity of an active sites than the adsorption energy.

Journal Article↗
PubMed2000

Adsorption of thermomonospora fusca E(5) cellulase on silanized silica.

The adsorption kinetics and dodeceyltrimethylammonium-bromide-mediated elution of Thermomonospora fusca E(5) cellulase were recorded in situ, at hydrophobic, silanized silica. Experiments were performed at different solution concentrations, ranging from 0.001 to 0.70 mg/mL. Plateau values of adsorbed mass generally increased with increasing solution concentration, with the adsorbed layer being only partially eluted by buffer. Treatment with surfactant removed more of the adsorbed enzyme in each case, with the remaining adsorbed mass varying little among experiments. Adsorption of E(5) into this nonremovable state was suggested to occur early in the adsorption process and continue until some critical surface concentration was reached. Beyond this critical value of adsorbed mass, adsorption progressed with the protein adopting more loosely bound states. Adsorption kinetic data were interpreted with reference to an adsorption mechanism allowing for irreversible adsorption into two dissimilar states. These states were distinguished by differences in occupied interfacial area, and binding strength, presumably a result of differences in structure. Comparison of the data to the kinetic model based on this mechanism showed that the fraction of adsorbed molecules present in the more tightly bound state decreased as adsorption occurred from solutions of increasing concentration. However, the absolute values of more tightly bound molecules were less dependent on adsorption conditions.

Actinomycetales↗
PubMed2005

Adsorption of poly(ethylene glycol)-modified ribonuclease A to a poly(lactide-co-glycolide) surface.

Protein adsorption is a source of variability in the release profiles of therapeutic proteins from biodegradable microspheres. We employ optical reflectometry and total internal reflection fluorescence to explore the extent and kinetics of ribonuclease A (RNase A) adsorption to spin-cast films of poly(lactide-co-glycolide) (PLG) and, in particular, to determine how covalent grafting of polyethylene glycol (PEG) to RNase A affects adsorption. Adsorption kinetics on PLG surfaces are surface-limited for RNase A but transport-limited for unconjugated PEG homopolymers and for PEG-modified RNase A, indicating that PEG anchors the conjugates to the surface during the transport-limited regime. PEG modification of RNase A decreases the total number of adsorbed molecules per unit area but increases the areal surface coverage because the grafted PEG chains exclude additional surface area. Total internal reflection fluorescence-based exchange measurements show that there is no exchange between adsorbed and solution-phase protein molecules. This indicates an unusually tenacious adsorption. Streaming current measurements indicate that the zeta potential of the PLG surface becomes increasingly negative as the film is exposed to water for several weeks, as expected. Aging of the PLG surface results in increased adsorption of unmodified RNase A but decreased adsorption of unconjugated PEG homopolymers and of PEG-RNase A conjugates, relative to the extent of adsorption on freshly prepared PLG surfaces. Adsorption results correlate well with an increase in the rate, total extent and preservation of bioactivity of RNase A released from PLG microspheres for the PEG-modified version of RNase A.

Adsorption↗
PubMed2006

Rapid and effective adsorption of lead ions on fine poly(phenylenediamine) microparticles.

Fine microparticles of poly(p-phenylenediamine) (PpPD) and poly(m-phenylenediamine) (PmPD) were directly synthesized by a facile oxidative precipitation polymerization and their strong ability to adsorb lead ions from aqueous solution was examined. It was found that the degree of adsorption of the lead ions depends on the pH, concentration, and temperature of the lead ion solution, as well as the contact time and microparticle dose. The adsorption data fit the Langmuir isotherm and the process obeyed pseudo-second-order kinetics. According to the Langmuir equation, the maximum adsorption capacities of lead ions onto PpPD and PmPD microparticles at 30 degrees C are 253.2 and 242.7 mg g(-1), respectively. The highest adsorptivity of lead ions is up to 99.8 %. The adsorption is very rapid with a loading half-time of only 2 min as well as initial adsorption rates of 95.24 and 83.06 mg g(-1) min(-1) on PpPD and PmPD particles, respectively. A series of batch experiment results showed that the PpPD microparticles possess an even stronger capability to adsorb lead ions than the PmPD microparticles, but the PmPD microparticles, with a more-quinoid-like structure, show a stronger dependence of lead-ion adsorption on the pH and temperature of the lead-ion solution. A possible adsorption mechanism through complexation between Pb(2+) ions and ==N-- groups on the macromolecular chains has been proposed. The powerful lead-ion adsorption on the microparticles makes them promising adsorbents for wastewater cleanup.

Adsorption↗
PubMedDate not supplied

The kinetics of baboon fibrinogen adsorption to polymers: in vitro and in vivo studies.

Fibrinogen adsorption on polymers from blood may mediate or potentiate thrombosis because of its involvement in both the intrinsic clotting system and the formation of platelet aggregates. While the kinetics of fibrinogen adsorption from plasma in vitro have previously been found to be very different on polar and nonpolar surfaces [T. A Horbett, "The kinetics of adsorption of plasma proteins to a series of hydrophilic-hydrophobic copolymers," ACS Org. Coat. Plas. Chem. 40, 642-646 (1979)] the significance of this difference with respect to thrombogenesis in vivo has not been clarified. In this study, the kinetics of deposition of baboon 125I fibrinogen from plasma in vitro or from blood in vivo on a series of polymers was measured. The polymers chosen for this study had previously been found to have a large range in surface polarity and reactivity in the in vivo baboon shunt model. The kinetics of fibrinogen adsorption in vitro were observed to be of three types, depending on the polymer: high initial adsorption decreasing to a lower steady state value; constant throughout the time course; low initial adsorption rising steadily to a plateau value. In vivo, fibrinogen deposition kinetics were of two types: low, constant deposition throughout the time course, independent of heparinization; low deposition initially followed by a second phase of greatly increased deposition (probably as fibrin) which was prevented or greatly decreased by heparinizing the animals. Polymers for which fibrinogen adsorption increased to a plateau in vitro were found to have a heparin inhibitable second phase of enhanced in vivo fibrinogen deposition. These polymers also have been found in previous studies to enhance the rate of platelet destruction when used as in vivo shunts on baboons. Conversely, most polymers with high initial in vitro fibrinogen adsorption followed by a decrease had low fibrinogen deposition behavior in vivo and were also minimally destructive of platelets. The adsorption kinetics of fibrinogen to polymers from blood in vivo and in vitro and the consumption of platelets in vivo induced by the polymers all vary with polymer polarity. More polar polymers had in vitro fibrinogen kinetics characterized by a rise to a plateau, in vivo fibrinogen deposition characterized by a second stage of great increase inhibitable by heparin, and enhanced platelet consumption. The correlation of three separate indicators of surface thrombogenicity with surface polarity suggests that more polar materials may be more thrombogenic because of an influence on the way in which fibrinogen interacts with these surfaces.

Adsorption↗
PubMed1979

Evaluation of adsorption from dispersion charge profile.

The evaluation of adsorption behavior from the charge profile of an adsorbent dispersion determined as a function of the adsorbate concentration was investigated by the streaming current measurement, using methylene blue and erythrosine as adsorbates and activated charcoal, microcrystalline cellulose, and polyvinylpolypyrrolidone as adsorbents. Adsorption capacity was evaluated using streaming current versus solute concentration plots of dye solutions and of corresponding dye solutions equilibrated with the adsorbent. It was also determined by adsorption isotherm measurement and application of the Langmuir equation. Good agreement was obtained between the adsorption capacity values from streaming current data and adsorption isotherm measurements for microcrystalline cellulose, suggesting that adsorption here was a surface phenomenon without water-soluble extractives affecting particle charge. Similar agreement was not obtained for charcoal adsorption, and this result was attributed to the unusual adsorption behavior of charcoal. Since polyvinylpolypyrrolidone gave a dispersion with high particle charge, the streaming current method could not be used with this system. The charge profile could be useful in characterizing powders for unusual adsorption behavior and possible water-soluble extractives as well as for surface area estimation in the absence of these factors.

Adsorption↗
PubMed2002

Adsorption of fluoride, phosphate, and arsenate ions on a new type of ion exchange fiber.

A new type of ion exchange fiber for the removal of fluoride, phosphate, and arsenate ions has been developed. A batch adsorption technique for investigating adsorption kinetic and equilibrium parameters and determining pH adsorption edges is applied. It is shown that the adsorption properties of the ion exchange fiber for fluoride, phosphate, and arsenate ions depend on the pH value and anion concentration. The adsorption of arsenate on the sorbent reaches a maximum of 97.9% in the pH value range of 3.5 to 7.0. The adsorption percentage of phosphate is more than 99% in the pH range of 3.0 to 5.5. The adsorption of fluoride on the ion exchange fiber is found to be 90.4% at pH 3.0. The Freundlich model can describe the adsorption equilibrium data of fluoride, arsenate, and phosphate anions. The sorption of the three anions on the ion exchange fiber is a rapid process, and the adsorption kinetic data can be simulated very well by the pseudo-second-order rate equation. The column performance is carried out to assess the applicability of the ion exchange fiber for the removal of fluoride, phosphate, and arsenate ions from synthetic wastewaters with satisfactory removal efficiency. The desorption experiment shows that fluoride ion sorbed by the fiber column can be quantitatively desorbed with 5 mL of 0.50 mol/L NaOH at elution rate of 1 mL/min, and 30 mL of NaOH is necessary for the quantitative recovery of phosphate and arsenate ions.

Acrylic Resins↗
PubMed1994

Protein adsorption on low temperature isotropic carbon. III. Isotherms, competitivity, desorption and exchange of human albumin and fibrinogen.

In this paper we consider the adsorption of albumin and fibrinogen on low temperature isotropic carbon (LTIC). A subsequent paper considers the adsorption of other plasma proteins [Feng L, Andrade JD, Colloids and Surfaces (in press)]. Carbon fragments and silica plates were used as adsorbents. Adsorption was carried out by incubating the adsorbents in solutions of 125I-labelled and unlabelled proteins (single component system), or with buffer-diluted human plasma (multicomponent system). Adsorbed proteins then underwent displacement by buffer, by single protein solutions or by dilute plasma. Results show that the LTIC substrate adsorbs a large amount of proteins before saturation, which may be due to multilayer adsorption. LTIC also irreversibly holds adsorbed proteins against the exchange agents used; little adsorbed proteins can be displaced, even after a very short adsorption time. There is no preferential adsorption for either albumin or fibrinogen on LTIC from their binary solutions, suggesting that both proteins have high affinities for the surface. Such strong interactions between LTIC and proteins are not attributed to electrostatic interactions. On the other hand, protein adsorption on the silica surface is selective and reversible, with a much higher affinity for fibrinogen than albumin and an even higher affinity for some other plasma proteins. The paper also discusses the effect of sequential protein addition to a solution on the surface concentration and suppression of adsorption of both proteins in the presence of other plasma proteins. A very important conclusion is that the LTIC surface is very active towards proteins adsorption.

Adsorption↗
PubMed2004

Effect of dye compounds on the adsorption of atrazine by natural sediment.

The overall objective of this research is to investigate competitive adsorption between atrazine (AT) and dye compounds in the natural aquatic sediment. The sorbent was sediment obtained from Guanting Reservoir (Beijing, China), which contained 25% sand, 67% silt, 8% clay, and 2.06% organic carbon. Batch adsorption experiments were conducted at various Ca2+ concentration, pH levels, temperatures, and introducing conditions of dye compounds. Compared with the dye-free system, both of dyes including Congo red (CR) and methylene blue (MB) reduce the adsorption of atrazine over the range of dye concentrations examined, with the adsorption percentage of atrazine decreasing about 14-30%. And the competition between AT and MB is much stronger than that between AT and CR. The adsorption experimental data points have been fitted to the Freundlich equation in order to calculate the adsorption capacities (Kf) of the samples; Kf values range from 1.669 micromol/kg for the MB-AT sample up to 3.738 micromol/kg for the AT-alone sample. By contrast with the single-solute adsorption isotherm, both simultaneous adsorption and dye preloading inhibit the adsorption of atrazine. As for AT preloading, the impacts of CR and MB are different on the desorption of atrazine. As compared to the atrazine desorption without dye compounds, a certain amounts of atrazine molecules are replaced by MB in AT preloading system, while in CR solution AT is adsorbed strongly on the sediment and could not be replaced by CR. The result suggests that micropore constriction by CR reduces the desorption rate of atrazine.

Adsorption↗
PubMed2004

Adsorption of bisphenol-A, 17 beta-estradiole and 17 alpha-ethinylestradiole to sewage sludge.

Adsorption of bisphenol-A (CAS 85-05-7), 17 beta-estradiole (CAS 50-28-2) and 17 alpha-ethinylestradiole (CAS 57-63-6) to activated and to inactivated sludge from wastewater treatment plants (WWTPs) was investigated, thus allowing to distinguish between pure adsorption and biosorption. For the investigated substances the determination of the adsorption kinetics is based on experiments performed according to the OECD guideline 106 and on free concentration measurements in the liquid phase. The description of the adsorption behaviour occurred via Freundlich Adsorption Isotherms. Additionally specific adsorption coefficients KD, KOM and KOC were calculated. The results of these calculations were compared to KOC values obtained with a HPLC method according to the OECD guideline 121. All substances showed a high adsorption affinity to the adsorbent and in spite of the application of very high initial concentrations no saturation level could be reached. Within a contact time of 24 h, no difference between the adsorption to activated and inactivated sludge could be detected. The calculated KD values were within a range of about KD = 1000 l kg(-1) for the investigated compounds and showed a clear concentration dependency in the case of bisphenol-A. Adsorption was also found to depend on pH. The experimentally determined KOC values of the investigated substances were significantly higher than the results obtained with the HPLC method described in OECD guideline 121.

Adsorption↗
PubMed2004

Adsorption and cosorption of cadmium and glyphosate on two soils with different characteristics.

Glyphosate [N-(phosphonomethyl)glycine] (GPS; H3G) is a widely used pesticide throughout the world. It affects metal behaviors in soil-plant system due to its functional groups, which react with metal ions to form metal complexes. Adsorption and cosorption of cadmium and glyphosate on a Wushan soil (WS soil, Anthrosol) and a Zhuanhong soil (ZH soil, Udic Ferrisol) as affect by solution pH were studied by means of batch adsorption experiments. It indicated that the adsorption quantity of Cd or glyphosate was highly relevant to soil characteristics. The WS soil had higher adsorption capacity of Cd than the ZH soil, due to its high organic matter content and cation exchange capacity (CEC). In contrast, the adsorption quantity of glyphosate on the WS soil was less than that on the ZH soil, because the WS soil has lower iron and aluminum oxides content but higher pH than the ZH soil. The herbicide glyphosate affected Cd adsorption on the two soils when they coexisted in a same soil solution, which was attributed to a glyphosate-induced pH-decrease and the corresponding decline in negative surface charges of the soil. Beside that, glyphosate reacted with solution Cd to form the water-soluble complexes that had lower affinity to soil surface in comparison with Cd itself. On the other hand, the presence of Cd in the soil solution also affected the adsorption of glyphosate on the soils. The presence of Cd increased adsorption quantity of glyphosate on the WS and ZH soils, which was resulted from the decrease of equilibrium solution pH caused by Cd2+ exchange with H+ ions of soil surface. In addition to that, glyphosate adsorption possibly takes place on sites where Cd was previously adsorbed and acted as a bridge between the soil and glyphosate.

Adsorption↗
PubMed2005

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

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

Adsorption↗
PubMed2006

Numerical determination of the adsorption isotherms of tryptophan at different temperatures and mobile phase compositions.

Single-component adsorption isotherm data were acquired by frontal analysis (FA) for tryptophan on a C(18)-Kromasil packed column, using acetonitrile-water solutions of various compositions (2.5, 5, and 7.5% ACN+1% acetic acid) and at five different temperatures between 25 and 65 degrees C. The adsorption isotherm model accounting best for these data is the bi-Moreau model, showing that two types of adsorption sites coexist on the surface and that strong adsorbate-adsorbate interactions take place. Large concentration band profiles of tryptophan were obtained for the three mobile phase compositions, at five different temperatures and the best values of the adsorption isotherm coefficients were determined by the inverse method (IM) of chromatography. The advantages and drawbacks of using the FA and the IM for determining the coefficients of the adsorption isotherm of tryptophan under the experimental conditions selected are discussed. The results of the FA and IM measurements are in good agreement. Both indicate that the retention time of tryptophan decreases rapidly with increasing acetonitrile concentration in the mobile phase as well as the saturation capacities of the two types of adsorption sites, with the highest values of the two saturation capacities being found for the lowest ACN content and the lowest temperature. The adsorption constant on the low-energy sites decreases with increasing acetonitrile content and temperature. In contrast, the adsorption constant on the high-energy sites increases with increasing ACN content of the mobile phase but decreases with increasing temperature. The solute-solute interaction parameters for the low and the high-energy adsorption sites increase rapidly with increasing ACN concentration in the mobile phase and with increasing temperature.

Adsorption↗
PubMed2006

Synthesis of tentacle-type magnetic beads as immobilized metal-chelate affinity support for cytochrome c adsorption.

Magnetic poly(2-hydroxyethylmethacrylate) (mPHEMA) beads with an average diameter of 100-140 microm were produced by suspension polymerization in the presence of magnetite particles (i.e. Fe3O4). Specific surface area and average pore size of the magnetic beads was found to be 50 m2/g and 819 nm, respectively. Ester groups in the mPHEMA structure were converted to imine groups by reacting with poly(ethyleneimine) (PEI) in the presence of NaH. Amino (-NH2) content of PEI-attached mPHEMA beads was determined as 102 mg PEI/g. Then, Cu2+ ions were chelated on the magnetic beads in the range of 20-793 micromol Cu2+/g. Cytochrome c (cyt c) adsorption was performed on the metal chelating beads from aqueous solutions containing different amounts of cyt c at different pHs, Cu2+ loadings and temperatures. Cyt c adsorption on the mPHEMA/PEI beads was 4.6 mg/g. Cu2+ chelation increased the cyt c adsorption significantly (40.1 mg/g). Adsorption capacity increased with Cu2+ loading and then reached a saturation value. Cyt c adsorption decreased with increasing temperature. Cyt c molecules could be reversibly adsorbed and eluted ten times with the magnetic adsorbents without noticeable loss in their cyt c adsorption capacity. The applicability of two kinetic models including pseudo-first order and pseudo-second order model was estimated on the basis of comparative analysis of the corresponding rate parameters, equilibrium capacity and correlation coefficients. Results suggest that chemisorption processes could be the rate-limiting step in the adsorption process. In the last part of this article, cyt c adsorption experiments were performed in a magnetically stabilized fluidized bed (MSFB) system at optimum conditions determined from the batch experiments. The adsorption capacity decreased significantly from 46.8 to 15.4 mg/g polymer with the increase of the flow-rate from 0.5 to 4.0 ml/min. The resulting magnetic chelator beads possessed excellent long-term storage stability.

Adsorption↗
PubMed2004

Effects of carboxyl groups on the adsorption behavior of low-molecular-weight substances on a stainless steel surface.

The adsorption isotherms of various carboxylic acids and several amines on a stainless steel surface were taken as a function of pH and the ionic strength of the solution at 30 degrees C. In particular, the effect of the number of carboxyl groups on the adsorption behavior was investigated. Monocarboxylic acids such as benzoic acid and n-butyric acid were reversibly adsorbed on the stainless steel particles and showed a Langmuir-type adsorption isotherm, i.e., Q=KqmC/(1+KC), where Q and C are, respectively, the amount of adsorbate adsorbed and the equilibrium concentration in the bulk solution, qm, the maximum adsorbed amount, and K is the adsorption equilibrium constant. Carboxylic acids having plural carboxyl groups had much higher affinity to the surface and were adsorbed in both reversible and irreversible modes. The adsorption isotherms for the carboxylic acids having plural carboxyl groups could be expressed by a modified Langmuir-type adsorption isotherm, i.e., Q=q(irrev)+Kq(rev)C/(1+KC), where q(irrev) and q(rev) are, respectively, the maximum amounts adsorbed irreversibly and reversibly. The K and q(irrev) values increased with an increase in the number of carboxyl groups except for isophthalic acid and terephthalic acid. On the basis of the pH dependencies of K, qm, q(irrev), and q(rev) as well as the surface properties of the stainless steel, both reversible and irreversible adsorptions were considered to occur through the electrostatic interaction between negatively charged carboxyl groups and the positively charged sites on the surface. The dependency of the q(irrev) value on ionic strength was discussed on the basis of the differences in their adsorbed state with the interaction forces to the surface and repulsive forces among the adsorbed molecules. The adsorption of amine components was quite weak. The RA-IR and molecular dynamics calculation were done to investigate the adsorption states of phthalic acid, trimellitic acid, and mellitic acid.

Adsorption↗
PubMed2005

Adsorption of benzoic acid onto high specific area activated carbon cloth.

The adsorption of benzoic acid from aqueous solution onto high area carbon cloth at different pH values has been studied. Over a period of 125 min the adsorption process was found to follow a first-order kinetics and the rate constants were determined for the adsorption of benzoic acid at pH 2.0, 3.7, 5.3, 9.1, and 11.0. The extents of adsorption and the percentage coverage of carbon cloth surfaces were calculated at 125 min of adsorption. Adsorption isotherms at pH values of 2.0, 3.7, and 11.0 were derived at 25 degrees C. Isotherm data were treated according to Langmuir and Freundlich equations and the parameters of these equations were evaluated by regression analysis. The fit of experimental isotherm data to both equations was good. It was found that both the adsorption rate and the extent of adsorption at 125 min were the highest at pH 3.7 and decreased at higher or lower pH values. The types of interactions governing in the adsorption processes are discussed considering the surface charge and the dissociation of benzoic acid at different pH values.

Adsorption↗
PubMed2005

Modes of conformational changes of proteins adsorbed on a planar hydrophobic polymer surface reflecting their adsorption behaviors.

Infrared spectra of hen egg white lysozyme and bovine serum albumin (BSA) adsorbed on a solid poly tris(trimethylsiloxy)silylstyrene (pTSS) surface in D2O solution were measured using attenuated total reflection (ATR) Fourier transform infrared spectroscopy. From the area and shape of the amide I' band of each spectrum, the adsorption amount and the secondary structure were determined simultaneously, as a function of adsorption time. We could show that the average conformation for all the adsorbed lysozyme molecules was solely determined by the adsorption time, and independent of the bulk concentration, while the adsorption amount increased with the bulk concentration as well as the adsorption time. These results suggest that lysozyme molecules form discrete assemblies on the surface, and that the surface assemblies grow over several hours to have a definite architecture independent of the adsorption amount. As for BSA, the extent of the conformational change was solely determined by the adsorption amount, regardless of the bulk concentration and the adsorption time. These differences in the adsorption properties of lysozyme and BSA may reflect differences in their conformational stabilities.

Adsorption↗