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PubMed2004

Adsorption of lead and cadmium ions in aqueous solutions onto modified lignin from alkali glycerol delignication.

Adsorptions of toxic metal ions (Pb(II) and Cd(II)) onto modified lignin from beech and poplar woods by alkali glycerol delignification are presented in this paper. The material exhibits good adsorption capacity and the adsorption data follow the Langmuir model. The maximum adsorption capacities are 8.2-9.0 and 6.7-7.5 mg/g of the modified lignin for Pb(II) and Cd(II), respectively. The maximum adsorption percentage is 95.8 for Pb(II) for 4 h at 330 K and is 95.0 for Cd(II) for 10 h at 290 K. The adsorption of both the metal ions increased with increasing temperature indicating endothermic nature of the adsorption process. The maximum adsorption percentages of Pb(II) and Cd(II) ions decrease with time till 48 and 42 h and then again increase slightly with time. The adsorption of both heavy metal ions increases with pH. The adsorption of Pb(II) ions reached a maximum at a 5.0 value of pH.

Adsorption↗
PubMed2005

Equilibrium studies for trimethoprim adsorption on montmorillonite KSF.

In this study, the adsorption of trimethoprim (TMP) on montmorillonite KSF was studied under different conditions (pH, ionic strength, temperature). The results indicate that a pH value of 5.04 is optimum value for the adsorption of TMP on KSF. The adsorption kinetics was interpreted using pseudo-first-order kinetic model, pseudo-second-order kinetic model and intraparticle diffusion model. The pseudo-second-order model provides the best correlation with the experimental data of KSF adsorption. The adsorption data could be fitted with Freundlich, Langmuir and Dubinin-Radushkevich equation to find the characteristic parameters of each model. It was found that linear form of Langmuir isotherm seems to produce a better model than linear form of Freundlich equation. From the Langmuir and Freundlich equation, the adsorption capacity values raised as the solution temperature decreased. From DR isotherm, it was also determined that the type of adsorption can be considered as ion-exchange mechanism. Determination of the thermodynamic parameters DeltaH(0), DeltaS(0) and DeltaG(0) showed that adsorption was spontaneous and exothermic in nature. It was also added that adsorption of TMP by KSF may involve physical adsorption.

Adsorption↗
PubMed2005

The effect of some operating variables on the adsorption of lead and cadmium ions on kaolinite clay.

Modification of kaolinite clay mineral with orthophosphate (p-modified sample) enhanced adsorption of Pb and Cd ions from aqueous solutions of the metal ions. Increasing pH of solutions of metal ions, increasing adsorbent dose and increasing concentration of metal ion, increased the adsorption of metal ions. Adsorption of both metal ions simultaneously on both unmodified and p-modified samples indicates that adsorption of one metal ion is suppressed to some degree by the other. The presence of electrolyte and their increasing concentration reduced the adsorption capacities of both unmodified and p-modified samples for the metal ions. Ca-electrolytes had more negative effect on the adsorption capacities of the adsorbents than Na-electrolytes. Ca-electrolytes reduced adsorption capacities of the adsorbents for Pb and Cd ions. From Langmuir plots it was observed that these electrolytes increased the binding energy constant of the metal ions unto the adsorbents especially on the p-modified samples. The rate of adsorption of Pb and Cd ions on p-modified adsorbent were increased and equilibrium of metal ion solution were more quickly reached (8min for Pb ions and 12min for Cd ions) with p-modified adsorbent as against 20min for adsorption of both metal ions on unmodified adsorbent when 200mg/L of metal ion solutions were used during the kinetic studies. When adsorption data were fitted against Langmuir, Freundlich, Toth and Langmuir-Freundlich isotherms, satisfactory fits were found with the Freundlich isotherm. However, at low concentration of metal ions, data also showed satisfactory fits to Langmuir isotherm.

Adsorption↗
PubMed2006

Batch study of liquid-phase adsorption of methylene blue using cedar sawdust and crushed brick.

This paper presents a study on the batch adsorption of basic dye, methylene blue, from aqueous solution (40 mg L(-1)) onto cedar sawdust and crushed brick in order to explore their potential use as low-cost adsorbents for wastewater dye removal. Adsorption isotherms were determined at 20 degrees C and the experimental data obtained were modelled with the Langmuir, Freundlich, Elovich and Temkin isotherm equations. Adsorption kinetic data determined at a temperature of 20 degrees C were modelled using the pseudo-first and pseudo-second-order kinetic equations, liquid-film mass transfer and intra-particle diffusion models. By considering the experimental results and adsorption models applied in this study, it can be concluded that equilibrium data were represented well by a Langmuir isotherm equation with maximum adsorption capacities of 142.36 and 96.61 mg g(-1) for cedar sawdust and crushed brick, respectively. The second-order model best describes adsorption kinetic data. Analysis of adsorption kinetic results indicated that both film- and particle-diffusion are effective adsorption mechanisms. The Influence of temperature and pH of the solution on adsorption process were also studied. The extent of the dye removal decreased with increasing the solution temperature and optimum pH value for dye adsorption was observed at pH 7 for both adsorbents. The results indicate that cedar sawdust and crushed brick can be attractive options for dye removal from dilute industrial effluents.

Adsorption↗
PubMed2006

Equilibrium and kinetics studies for adsorption of direct blue 71 from aqueous solution by wheat shells.

This paper deals with the application of wheat shells (WS), an agricultural by-product, for the removal of direct blue 71 (DR) from aqueous solution. The characteristics of WS surface, such as surface area, Bohem titration and scanning electron microscopy (SEM) were obtained. The removal of direct blue 71 onto WS from aqueous solution was investigated by using parameters, such as pH, temperature, adsorbent dose, contact time and initial concentration. The adsorption process attains equilibrium within 36 h. The extent of dye removal decreased with increasing adsorbent dosage and also increased with increasing contact time, temperature, in solution concentration. Optimum pH value for dye adsorption was determined between 6 and 8. The experimental data were analysed by the Langmuir and Freundlich models of adsorption. It was found that the Langmuir equation fit better than the Freundlich equation. Maximum adsorption capacity (Q(m)) was calculated as at different temperatures (293, 303 and 313 K) 40.82, 45.66 and 46.30 mgg(-1), respectively. In addition, the adsorption data obtained at different temperatures of DR by WS were applied to pseudo first-order, pseudo second-order and Weber-Morris equations, and the rate constants of first-order adsorption (k(1)), the rate constants of second-order adsorption (k(2)) and intraparticle diffusion rate constants (k(3)) at these temperatures were calculated, respectively. The rates of adsorption were found to conform to pseudo second-order kinetics with good correlation (R(2)>or=0.9904). Also, free energy of adsorption (DeltaG degrees), enthalpy (DeltaH degrees), and entropy (DeltaS degrees) changes were determined to predict the nature of adsorption. Furthermore, the results indicate that WS could be employed as a low-cost alternative to other adsorbents in the removal of direct blue 71 from aqueous solution.

Adsorption↗
PubMed2006

Microcolumn studies of dye adsorption onto manganese oxides modified diatomite.

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

Adsorption↗
PubMed2002

Analysis of diffusion models for protein adsorption to porous anion-exchange adsorbent.

The ion-exchange adsorption kinetics of bovine serum albumin (BSA) and gamma-globulin to an anion exchanger, DEAE Spherodex M, has been studied by batch adsorption experiments. Various diffusion models, that is, pore diffusion, surface diffusion, homogeneous diffusion and parallel diffusion models, are analyzed for their suitabilities to depict the adsorption kinetics. Protein diffusivities are estimated by matching the models with the experimental data. The dependence of the diffusivities on initial protein concentration is observed and discussed. The adsorption isotherm of BSA is nearly rectangular, so there is little surface diffusion. As a result, the surface and homogeneous diffusion models do not fit to the kinetic data of BSA adsorption. The adsorption isotherm of gamma-globulin is less favorable, and the surface diffusion contributes greatly to the mass transport. Consequently, both the surface and homogeneous diffusion models fit to the kinetic data of gamma-globulin well. The adsorption kinetics of BSA and gamma-globulin can be very well fitted by parallel diffusion model, because the model reflects correctly the intraparticle mass transfer mechanism. In addition, for both the favorably bound proteins, the pore diffusion model fits the adsorption kinetics reasonably well. The results here indicate that the pore diffusion model can be used as a good approximate to depict protein adsorption kinetics for protein adsorption systems from rectangular to linear isotherms.

Adsorption↗
PubMed2003

Adsorption of cobalt from aqueous solutions onto sepiolite.

Adsorption of Co(II) ions from aqueous sepiolite suspensions has been systematically investigated as a function of several variables including activation conditions, solid to liquid ratio, pH and temperature. The results are analyzed to identify the mechanism of cobalt uptake by sepiolite. Both abstraction and real adsorption isotherms were constructed to isolate the precipitation of cobalt from the real adsorption. Also, for the first time a plausible correlation between the released Mg(II) ions from sepiolite matrix and those adsorbed Co(II) ions is made. A one to one ion exchange mechanism is found to describe the results. The data obtained from adsorption isotherms at different temperatures were fitted to various adsorption models to calculate thermodynamic quantities such as the free energy of adsorption, heat of adsorption and entropy of adsorption. The thermodynamic data indicate that Co(II) adsorption onto sepiolite is entropically driven and characterized by physical adsorption.

Adsorption↗
PubMed2003

Activated carbon adsorption of trichloroethylene (TCE) vapor stripped from TCE-contaminated water.

Ground water contaminated with trichloroethylene (TCE) used in electronic, electric, dry cleaning and the like industries is often treated by air-stripping. In this treatment process, TCE in its vapor form is stripped from ground water by air stream and sometimes emitted into the atmosphere without any additional treatments. Activated carbon adsorption is one of the practical and useful processes for recovering the TCE vapor from the exhaust air stream. However, adsorption of the TCE vapor from the stripping air stream onto activated carbons is not so simple as that from dry air, since in the exhaust air stream the TCE vapor coexists with water vapor with relatively high concentrations. The understanding of the adsorption characteristics of the TCE vapor to be adsorbed on activated carbon in the water vapor-coexisting system is essential for successfully designing and operating the TCE recovery process. In this work, the adsorption equilibrium relations of the TCE vapor adsorption on activated carbons were elucidated as a function of various relative humidity. Activated carbon fibers (ACFs) were used as model activated carbon. The adsorption equilibrium relations were studied by the column adsorption method. The adsorption isotherms of TCE vapor adsorbed on sample ACFs were successfully correlated by the Dubinin-Radushkevich equation for both cases with and without coexistent water vapor. No effects of coexistent water vapor were found on the limiting adsorption volume. However, the adsorption characteristic energy was significantly reduced by the coexistence of water vapor and its reduction was successfully correlated with the equilibrium amount of water vapor adsorbed under the dynamic condition.

Adsorption↗
PubMed2003

Adsorption of volatile organic compounds by pecan shell- and almond shell-based granular activated carbons.

The objective of this research was to determine the effectiveness of using pecan and almond shell-based granular activated carbons (GACs) in the adsorption of volatile organic compounds (VOCs) of health concern and known toxic compounds (such as bromo-dichloromethane, benzene, carbon tetrachloride, 1,1,1-trichloromethane, chloroform, and 1,1-dichloromethane) compared to the adsorption efficiency of commercially used carbons (such as Filtrasorb 200, Calgon GRC-20, and Waterlinks 206C AW) in simulated test medium. The pecan shell-based GACs were activated using steam, carbon dioxide or phosphoric acid. An almond shell-based GAC was activated with phosphoric acid. Our results indicated that steam- or carbon dioxide-activated pecan shell carbons were superior in total VOC adsorption to phosphoric acid-activated pecan shell or almond shell carbons, inferring that the method of activation selected for the preparation of activated carbons affected the adsorption of VOCs and hence are factors to be considered in any adsorption process. The steam-activated, pecan shell carbon adsorbed more total VOCs than the other experimental carbons and had an adsorption profile similar to the two coconut shell-based commercial carbons, but had greater adsorption than the coal-based commercial carbon. All the carbons studied adsorbed benzene more effectively than the other organics. Pecan shell, steam-activated and acid-activated GACs showed higher adsorption of 1,1,1-trichloroethane than the other carbons studied. Multivariate analysis was conducted to group experimental carbons and commercial carbons based on their physical, chemical, and adsorptive properties. The results of the analysis conclude that steam-activated and acid-activated pecan shell carbons clustered together with coal-based and coconut shell-based commercial carbons, thus inferring that these experimental carbons could potentially be used as alternative sources for VOC adsorption in an aqueous environment.

Adsorption↗
PubMedDate not supplied

Novel thymine-functionalized polystyrenes for applications in biotechnology. 2. Adsorption of model proteins.

This paper investigates the adsorption of bovine serum albumin (BSA) and bovine hemoglobin (BHb) model proteins onto novel thymine-functionalized polystyrene (PS-VBT) microspheres, in comparison with polystyrene (PS) microspheres. Maximum adsorption was obtained for both proteins near their corresponding isoelectric points (pI at pH = 4.7 for BSA and 7.1 for BHb). FTIR and adsorption isotherm analysis demonstrated that, although both proteins were physisorbed onto PS through nonspecific hydrophobic interactions, adsorption onto the functionalized copolymers occurred by both physisorption and chemisorption via hydrogen bonding. FTIR analysis also indicated conformational changes in the secondary structure of BSA and BHb adsorbed onto PS, whereas little or no conformation change was seen in the case of adsorption onto PS-VBT. Atomic force microscopy (AFM), consistent with the isotherm results, also demonstrated monolayer adsorption for both proteins. AFM images of BSA adsorbed onto copolymers with 20 mol % surface VBT loading showed exclusively end-on orientation. Adsorption onto copolymers with lower functionality showed mixed end-on and side-on orientation modes of BSA, and only the side-on orientation was observed on PS. The AFM results agreed well with theoretically calculated and experimentally obtained adsorption capacities. AFM together with calculated and observed adsorption capacity data for BHb indicated that this protein might be highly compressed on the copolymer surface. Adsorption from a binary mixture of BSA and BHb onto PS-VBT showed good separation at pH=7.0; approximately 90% of the adsorbed protein was BHb. The novel copolymers have potential applications in biotechnology.

Adsorption↗
PubMedDate not supplied

Dynamic adsorption behavior of poly(3-hydroxybutyrate) depolymerase onto polyester surface investigated by QCM and AFM.

Time-dependent adsorption behavior of poly(3-hydroxybutyrate) (PHB) depolymerase from Ralstonia pickettiiT1 on a polyester surface was studied by complementary techniques of quarts crystal microbalance (QCM) and atomic force microscopy (AFM). Amorphous poly(l-lactide) (PLLA) thin films were used as adsorption substrates. Effects of enzyme concentration on adsorption onto the PLLA surface were determined time-dependently by QCM. Adsorption of PHB depolymerase took place immediately after replacement of the buffer solutions with the enzyme solutions in the cell, followed by a gradual increase in the amount over 30 min. The amount of PHB depolymerase molecules adsorbed on the surface of amorphous PLLA thin films increased with an increase in the enzyme concentration. Time-dependent AFM observation of enzyme molecules was performed during the adsorption of PHB depolymerase. The phase response of the AFM signal revealed that the nature of the PLLA surface around the PHB depolymerase molecule was changed due to the adsorption function of the enzyme and that PHB depolymerase adsorbed onto the PLLA surface as a monolayer at a lower enzyme concentration. The number of PHB depolymerase molecules on the PLLA surface depended on the enzyme concentration and adsorption time. In addition, the height of the adsorbed enzyme was found to increase with time when the PLLA surface was crowded with the enzymes. In the case of higher enzyme concentrations, multilayered PHB depolymerases were observed on the PLLA thin film. These QCM and AFM results indicate that two-step adsorption of PHB depolymerase occurs on the amorphous PLLA thin film. First, adsorption of PHB depolymerase molecules takes place through the characteristic interaction between the binding domain of PHB depolymerase and the free surface of an amorphous PLLA thin film. As the adsorption proceeded, the surface region of the thin film was almost covered with the enzyme, which was accompanied by morphological changes. Second, the hydrophobic interactions among the enzymes in the adlayer and the solution become more dominant to stack as a second layer.

Adsorption↗
PubMedDate not supplied

Adsorption-desorption process using wood-based activated carbon for recovery of biosurfactant from fermented distillery wastewater.

Methods used for biosurfactant recovery include solvent extraction, precipitation, crystallization, centrifugation and foam fractionation. These methods cannot be used when distillery wastewater (DW) is used as the nutrient medium for biosurfactant production by Pseudomonas aeruginosa strain BS2, because recovery of biosurfactant by any of these methods imparts color to the biosurfactant. The biosurfactant has a nonaesthetic appearance with lowered surface active properties. These methods cannot be used for continuous recovery of biosurfactant during cultivation. Hence, a new downstream technique for biosurfactant recovery from fermented DW comprised of adsorption-desorption processes using wood-based activated carbon (WAC) was developed. This study involves batch experiments to standardize the factors affecting the rate of biosurfactant adsorption onto WAC. WAC was the most efficient adsorbent among various ones tested (i.e., silica gel, activated alumina and zeolite). The WAC (1% w v(-1)), equilibrium time (90 min), pH range of 5-10 and temperature of 40 degrees C were optimum to achieve 99.5% adsorption efficiency. Adsorption kinetics and intraparticle diffusion studies revealed the involvement of both boundary layer diffusion and intraparticle diffusion. The Langmuir adsorption isotherm of WAC indicated the formation of a monolayer coverage of the biosurfactant over a homogeneous carbon surface, while the Freundlich isotherm showed high adsorption at strong solute concentrations and low adsorption at dilute solute concentrations. WAC concentration of 4% w v(-1) facilitated complete removal of the biosurfactant from collapsed foam (contained 5-fold higher concentration of biosurfactant than was present in fermented DW). Biosurfactant adsorption was of chemisorption type. Acetone (polar solvent) was a specific viable eluant screened among various ones tested because it selectively facilitated maximum recovery, i.e., 89% biosurfactant from WAC. By acetone treatment, complete regeneration of WAC was feasible and WAC can be reused for biosurfactant recovery up to 3 cycles. The recovered biosurfactant showed improved surface-active property (i.e., much lower critical micelle concentration value of 0.013 verses 0.028 mg mL(-1) for biosurfactant recovered by classical methods). The reuse potential of WAC was assessed and results suggest that the carbon can be reused for three consecutive cycles for biosurfactant adsorption from fermented wastewater without any decrease in adsorption efficiency. Thus, this process forms a basis for continuous recovery of biosurfactant from fermented DW and concentrated foam. This process reduces the use of high cost solvent, avoids end product inhibition and minimizes product degradation.

Adsorption↗
PubMed2002

Adsorption-desorption of phosphate on airborne dust and riverborne particulates in East Mediterranean seawater.

The potential importance of adsorption-desorption behavior of phosphorus (P) on the East Mediterranean (E. Med) P cycle was investigated. Contrasting adsorption behavior between Saharan dust (SD) and Nile particulate matter (Nile PM) was observed. SD was a source of P to the region, which released an average of 3.3 +/- 0.3 micromolP/g into the surface seawater and showed no adsorption ability under the conditions close to the E. Med deep water. Saharan dust is therefore unlikely to be the reason for P limitation in the region. By contrast, Nile PM acted dual roles of a sink and source of P in different waters (surface seawater, deep seawater, and river water). A new crossover-type adsorption-desorption model explained the contrasting adsorption behavior and the dual nature of natural particles. The model indicates that when natural particles are transported between different waters, they can be a sink (adsorption) or a source (desorption) of phosphorus depending on the "specific concentration (lambda)", which is the ratio between the aqueous P concentration and the zero equilibrium P concentration (EPC0). EPC0 refers to the solute concentration value where the adsorption isotherm crosses over the aqueous concentration axis. When lambda > 1, adsorption occurs, whereas when lambda < 1, desorption occurs. The model added a general development to the methodology of adsorption isotherm, where, for the first time, effects of solute concentration, solid concentration, and aqueous medium (EPC0) on the adsorption and desorption of P in natural waters were simultaneously described by a single equation. Using the model, it was quantitatively reconstructed that particles emitted during the pre-1964 Nile floods could be a major source of P to Egyptian coastal waters (up to 4800 tonsP/yr), greater than the dissolved P flux (approximately 3200 tonsP/yr), but a trapper of dissolved phosphate in E. Med deep waters.

Adsorption↗
PubMed2002

Adsorbent-adsorbate interactions in the adsorption of Cd(II) and Hg(II) on ozonized activated carbons.

The present work investigated the effect of surface oxygenated groups on the adsorption of Cd(II) and Hg(II) by activated carbon. A study was undertaken to determine the adsorption isotherms and the influence of the pH on the adsorption of each metallic ion by a series of ozonized activated carbons. In the case of Cd(II), the adsorption capacity and the affinity of the adsorbent augmented with the increase in acid-oxygenated groups on the activated carbon surface. These results imply that electrostatic-type interactions predominate in this adsorption process. The adsorption observed at solution pH values below the pH(PZC) of the carbon indicates that other forces also participate in this process. Ionic exchange between -C pi-H3O+ interaction protons and Cd(II) ions would account for these findings. In the case of Hg(II), the adsorption diminished with an increase in the degree of oxidation of the activated carbon. The presence of electron-withdrawing groups on oxidized carbons decreases the electronic density of their surface, producing a reduction in the adsorbent-adsorbate dispersion interactions and in their reductive capacity, thus decreasing the adsorption of Hg(II) on the activated carbon. At pH values above 3, the pH had no influence on the adsorption of Hg(II) by the activated carbon, confirming that electrostatic interactions do not have a determinant influence on Hg(II) adsorption.

Adsorption↗
PubMed2004

Collagen fiber immobilized Myrica rubra tannin and its adsorption to UO2(2+).

Tannins, which are rich in ortho-hydroxyl groups, have a high affinity for UO2(2+). In this paper, Myrica rubra tannin was immobilized on collagen fiber by an aldehydic cross-linking reaction to prepare a novel adsorbent for uranium (UO2(2+)) recovery from wastewater. The adsorption equilibrium, the adsorption kinetics, and the effects of temperature and pH on the adsorption equilibrium were investigated in detail. It was found that the Myrica rubra tannin immobilized on collagen fiber exhibits an excellent adsorption capacity for UO2(2+). The adsorption capacity at 293 K and pH 5.0 was as high as 1.19 mmol UO2(2+)/g (283.3 mgU/g) when the initial concentration of UO2(2+) in solution was 7.5 mmol/L. The adsorption isotherms could be described by the Freundlich equation, and the increase of temperature promoted the adsorption to UO2(2+) . The adsorption kinetics data were fitted very well by the pseudosecond-order rate model, and the equilibrium adsorption capacity calculated by the pseudo-second-order rate model was almost the same as that determined by the actual measurement with the error < or = 4%. The pH has a significant effect on the adsorption process. According to our experiments, the suitable pH scope should be 5-8.

Adsorption↗
PubMed2004

Modeling maximum adsorption capacities of soot and soot-like materials for PAHs and PCBs.

Recent studies have shown that not partitioning but adsorption is the main mechanism for sorption of hydrophobic organic compounds to soot and soot-like materials. For compounds that adsorb by van derWaals forces only, variation in soot-water distribution coefficients will result from differences in these forces for adsorption, as well as the maximum number of accessible sites. This maximum number of accessible sites may a priori be expected to vary due to differences in both sorbent characteristics and sorbate dimensions. In this modeling study, variation in maximum adsorption capacities is explained from sorbent and sorbate properties. Maximum adsorption capacities were calculated using (a) literature values for soot-water distribution coefficients for polycyclic aromatic hydrocarbons and polychlorobiphenyls on 10 different soot and soot-like materials and (b) Langmuir affinities for adsorption at a carbonaceous surface estimated using a recently reported method. The variation in maximum adsorption capacities could be explained by the variation in sorbent specific surface area, sorbent organic carbon content, and the sorbent-sorbate contact area. Furthermore, increasing sorbate thickness was related to a decrease in maximum adsorption capacities, which points to adsorption in micropores. Maximum adsorption capacities decreased by 1-2 orders of magnitude as the contact area increased by 50%. This points to adsorption sites being hardly larger than sorbates.

Adsorption↗
PubMed2004

Beta-thujaplicin: new quantitative CZE method and adsorption to goethite.

Beta-thujaplicin (beta-TH) is a toxic tropolone derivative present in the heartwood of western red cedar (Thuja plicata) and is used as a preservative and antimicrobial additive in a number of commercial goods. beta-TH released from western red cedar timber used outdoor and from other products containing beta-TH may transfer to soil and leach to groundwater and surface waters. The objective of this study was to quantify the adsorption of beta-TH to goethite as a typical model for geosorbents. Adsorption was studied using pH-adjusted goethite suspensions with solid:solution ratios of 1:500, 0.01 M NaNO(3) electrolyte, and 20 degrees C. beta-TH was determined using a new capillary zone electrophoresis (CZE) method providing a detection limit of 0.21 microM. Near-sorption equilibrium was attained within 48 h. beta-TH showed maximum adsorption at low pH (3.8) and a 70% drop in adsorption from pH 6.2 to 8.8. The Langmuir type adsorption isotherm at pH 5.5 approached a maximum adsorption of 220 micromol/g (= 6.2 micromol/m(2)), which is more than twice the amount of phosphate adsorbed under similar conditions. The affinity of beta-TH for goethite is low as compared with organic ligands such as citrate, oxalate, and 2,4-dihydroxybenzoate. The adsorption data and FTIR analyses indicate that beta-TH is most likely adsorbed as monodentate mononuclear surface complexes at the surface of goethite. Hydrophobic adsorption is thought to contribute to the adsorption, in particular at low pH. The strong adsorption of beta-TH to goethite suggests low mobility in most soil environments, the risk of contamination increasing in soils with high pH (calcareous material), low contents of iron and aluminum oxides, phyllosilicates, and organic matter.

Adsorption↗