Adsorption of methylene blue from aqueous solution on pyrolyzed petrified sediment

The adsorption kinetics of methylene blue on pyrolyzed petrified sediment (PPS) has been performed using a batch-adsorption technique. The effects of various experimental parameters, such as initial dye concentration, contact time, and temperature were investigated. The pseudo-first-order and pseudo-second-order kinetic models were used to describe the kinetic data. The best correlation coefficient was obtained using the pseudo first-order kinetic model, which shows that the adsorption of methylene blue followed the pseudo-first-order rate expression and the rate constants were evaluated. The Langmuir and Freundlich adsorption isotherm models were applied to describe the equilibrium isotherms and the isotherm constants were determined. It was found that the data fitted well to Langmuir and Freundlich models. The activation energy of adsorption was also evaluated for the adsorption of methylene blue onto pyrolyzed sediment. It was found about 8.5 kJ mol(-1). Thermodynamics parameters DeltaG(o), DeltaH(o), DeltaS(o) were calculated, indicating that this process can be spontaneous and endothermic. The adsorption enthalpy and entropy were found as 14-18.5 kJ mol(-1) and 52.8-67 J mol(-1) K(-1), respectively. The results obtained from the adsorption process using PPS as adsorbent was subjected to student's t-test.     

Removal of Cr(VI) from aqueous solutions by adsorption onto hazelnut shell activated carbon: kinetic and equilibrium studies

The adsorption Cr(VI) from aqueous solutions onto hazelnut shell activated carbon was carried out by varying the parameters such as pH, initial Cr(VI) concentration and temperature. The experimental data fitted well to the pseudo first-order kinetic model and then the rate constants were evaluated. The Langmuir isotherm provided the best correlation for Cr(VI) onto the activated carbon. Adsorption capacity was calculated from the Langmuir isotherm as 170 mg/g at an initial pH of 1.0 for the 1000 mg/l Cr(VI) solution. Thermodynamic parameters were evaluated and the adsorption is endothermic showing monolayer adsorption of Cr(VI).     

Thermodynamics and kinetics of lysozyme adsorption onto two kinds of weak cation exchangers

The present work investigated the adsorption behaviors of lysozyme onto weak cation exchangers at different temperatures. The adsorption isotherm, adsorption thermodynamics and adsorption kinetics were studied. The results indicate that the adsorption of lysozyme onto acrylic acid copolymer based beads (Hydrolite D115) is spontaneous and exothermic, while that onto agarose based beads (CM Sepharose 6 Fast Flow) is also spontaneous, but endothermic. The pseudo second-order kinetic model fits well to the dynamic adsorption experimental data, and the kinetic results are also in concert with the adsorption thermodynamics.     

Equilibrium and kinetics studies of adsorption of copper (II) on chitosan and chitosan/PVA beads

The adsorption of Cu(II) ions from aqueous solution by chitosan and chitosan/PVA beads was studied in a batch adsorption system. Chitosan solution was blended with poly(vinyl alcohol) (PVA) in order to obtain sorbents that are insoluble in aqueous acidic and basic solution. The adsorption capacities and rates of Cu(II) ions onto chitosan and chitosan/PVA beads were evaluated. The Langmuir, Freundlich and BET adsorption models were applied to describe the isotherms and isotherm constants. Adsorption isothermal data could be well interpreted by the Langmuir model. The kinetic experimental data properly correlated with the second-order kinetic model, which indicates that the chemical sorption is the rate-limiting step. The Cu(II) ions can be removed from the chitosan and chitosan/PVA beads rapidly by treatment with an aqueous EDTA solution. Results also showed that chitosan and chitosan/PVA beads are favourable adsorbers.     

Adsorption behaviour of Fe(II) and Fe(III) ions in aqueous solution on chitosan and cross-linked chitosan beads

A batch adsorption system was applied to study the adsorption of Fe(II) and Fe(III) ions from aqueous solution by chitosan and cross-linked chitosan beads. The adsorption capacities and rates of Fe(II) and Fe(III) ions onto chitosan and cross-linked chitosan beads were evaluated. Chitosan beads were cross-linked with glutaraldehyde (GLA), epichlorohydrin (ECH) and ethylene glycol diglycidyl ether (EGDE) in order to enhance the chemical resistance and mechanical strength of chitosan beads. Experiments were carried out as function of pH, agitation period, agitation rate and concentration of Fe(II) and Fe(III) ions. Langmuir and Freundlich adsorption models were applied to describe the isotherms and isotherm constants. Equilibrium data agreed very well with the Langmuir model. The kinetic experimental data correlated well with the second-order kinetic model, indicating that the chemical sorption was the rate-limiting step. Results also showed that chitosan and cross-linked chitosan beads were favourable adsorbers.     

Adsorption kinetics of azinphosmethyl from aqueous solution onto pyrolyzed Horseshoe sea crab shell from the Atlantic Ocean

The adsorption behavior of azinphosmethyl on pyrolyzed Horseshoe Crab (Limulus polyphemus) outer shell, as a residue, from the Atlantic Ocean, collected along the Maine coast, USA, has been studied with regards to its kinetic and equilibrium conditions, taking into account adsorbate concentrations of 2 x 10(-3), 4 x 10(-3), 6 x 10(-3), and 8 x 10(-3), as well as temperatures of 30 degrees C, 40 degrees C, 50 degrees C, and 60 degrees C. The yield of adsorption of azinphosmethyl from aqueous solution ranged from 56.1% to 61% with temperature increasing. Kinetic studies showed that adsorption rate decreased as the initial azinphosmethyl concentration increased. It was found, that the adsorption reaction obeyed first-order kinetics. The overall rate constants were estimated for different temperatures. The activation energy for adsorption was about 1.52 kJmol(-1), which implies that azinphosmethyl mainly adsorbed physically onto Horseshoe Crab outer shell. Langmuir and Freundlich isotherms were applied to the experimental data and isotherm constants were calculated. The thermodynamic parameters DeltaG0, DeltaH0 and DeltaS0 for the adsorption reaction were evaluated based on equilibrium data and in connection with this result the thermodynamic aspects of adsorption reaction were discussed. The adsorption was found to be endothermic in nature. The adsorbent used in this study proved highly efficient for the removal of azinphosmethyl.     

Hydrolysis of particulate tributyrin in a fluidized lipase reactor.

Pancreatic lipase has been immobilized onto stainless steel beads by adsorption followed by crosslinking, and onto polyacrylamide by covalent bonding. The activities of the two types of immobilized enzyme toward the particulate substrate, tributyrin emulsion droplets, were determined experimentally, and rate constants based on Michaelis-Menten kinetics were calculated. The activity of the stainless steel-lipase was determined for various flow conditions and for various support sizes by the use of a differential fluidized bed recycle reactor. The rate constants calculated indicate that the experimental reaction rate is free from mass transfer influences, since the observed Michaelis constant does not vary with the fluidization velocity or with the support particle size. In addition, the Michaelis constant of the stainless steel-lipase was found to be equal to that of the free enzyme, suggesting that adsorption and subsequent crosslinking does not alter the enzyme-substrate affinity. The emulsion substrate mass transfer rates, calculated from the filtration theory, indicate that each substrate particle which contact the immobilized enzyme is hydrolyzed to a significant extent. The experimentally determined kinetic rate constants may be used directly to predict the size of integral fluidized bed reactors.     

Experimental Measurements of the Adsorption of Bacillus subtilis and Pseudomonas mendocina Onto Fe-Oxyhydroxide-Coated and Uncoated Quartz Grains

In this study, we compared the adsorption of the gram-positive bacterium Bacillus subtilis with adsorption of the gram-negative bacterium Pseudomonas mendocina onto Fe-oxyhydroxide-coated and uncoated quartz grains as a function of pH and bacteria: mineral mass ratio. We studied metabolically-inactive cells in order to focus on the initial bacterial attachment mechanisms. The data show that the presence of Fe-oxyhydroxide-coatings on quartz surfaces significantly enhances the adsorption of bacteria and that in general the extent of adsorption decreases with increasing pH and with decreasing bacteria: mineral mass ratio. B. subtilisadsorbs to a greater extent than does P. mendocina onto the surface of the Fe-coated quartz. The adsorption behavior appears to be controlled by the overall surface charge of both bacterial and mineral surfaces. We model the adsorption data using a semi-empirical chemical equilibrium model that accounts for the site speciation of the adsorbing surfaces. Models describing bacterial adsorption to Fe-oxyhydroxide-coated quartz can account for changes in pH and bacteria: mineral mass ratio using one set of equilibrium constants.     

Isotherm,Kinetic, and Thermodynamic Characteristics for Adsorption of 2,5-Xylenol onto Activated Carbon

The adsorption of the major tar compound, 2,5-xylenol, derived from the plant cell cultures of Taxus chinensis, onto activated carbon was examined at different initial 2,5-xylenol concentrations, durations, and temperatures. From the analysis of adsorption isotherms, the Langmuir isotherm model showed good fit to the equilibrium adsorption data. It was found that adsorption capacity decreased with increasing temperature, and the adsorption of 2,5-xylenol onto activated carbon was favorable. The obtained kinetic data for 2,5-xylenol adsorption with activated carbon agreed well with the pseudo-second-order kinetic model. By using intraparticle diffusion model, intraparticle diffusion and boundary layer diffusion did not play a dominant role in 2,5-xylenol adsorption. Thermodynamic parameters were calculated, which indicated that the adsorption was non-spontaneous, irreversible and exothermic nature. The isosteric heat of adsorption decreased with increase in surface loading, indicating a heterogeneous surface.     

Biospecific adsorption of lysozyme onto monoclonal antibody ligand immobilized on nonporous silica particles

It is very important to understand the equilibrium and dynamic characteristics of biospecific adsorption (affinity chromatography) for both scientific and application purposes. Experimental equilibrium and dynamic column data are presented on the adsorption of lysozyme onto antibody immobilized on nonporous silica particles. The Langmuir model is found to represent the equilibrium experimental data satisfactorily, and the equilibrium association constants and heats of adsorption have been estimated for two systems with different ligand densities. The effects of nonspecific interactions are more pronounced in the system with low-density ligand. The dynamic interaction kinetic parameters are estimated by matching the predictions of a fixed-bed model with the experimental breakthrough curves. The agreement between theory and experiment is good for the initial phases of breakthrough, where the mechanism of biospecific adsorption is dominant. In the later phase (saturation neighborhood) of breakthrough, the effects of nonspecific interactions appear to be greater in the low-density ligand system. The kinetics of the nonspecific interactions were estimated from the data of the later phase of breakthrough and were found to be considerably slower than those attributed to biospecific adsorption.     

Kinetics of sickle hemoglobin polymerization. II. A double nucleation mechanism

A double nucleation mechanism for the polymerization of sickle hemoglobin is described. The mechanism accounts for all of the major kinetic observations: the appearance of a delay, the high concentration dependence of the delay time, and the stochastic behavior of slowly polymerizing samples in small volumes. The mechanism postulates that there are two pathways for polymer formation: polymerization is initiated by homogeneous nucleation in the solution phase, followed by nucleation of additional polymers on the surface of existing ones. This second pathway is called heterogeneous nucleation. Since the surface of polymers is continuously increasing with time, heterogeneous nucleation provides a mechanism for the extreme autocatalysis that is manifested as an apparent delay in the kinetic progress curves. In this mechanism, each spherulitic domain of polymers is considered to be initiated by a single homogeneous nucleation event. The mechanism explains the irreproducibility of the delay time for single domain formation as arising from stochastic fluctuations in the time at which the homogeneous nucleus for the first polymer is formed. Integration of the linearized rate equations that describe this model results in a simple kinetic form: A[cosh(Bt)-1] (Bishop & Ferrone, 1984). In the accompanying paper (Ferrone et al., 1985) it was shown that the initial 10 to 15% of progress curves, with delay times varying from a few milliseconds to over 10(5) seconds, is well fit by this equation. In this paper, we present an approximate statistical thermodynamic treatment of the equilibrium nucleation processes that shows how the nucleus sizes and nucleation equilibrium constants depend on monomer concentration. The equilibrium model results in expressions for B and B2A as a function of monomer concentration in terms of five adjustable parameters: the bimolecular addition rate of a monomer to the growing aggregate, the fraction of polymerized monomers that serve as heterogeneous nucleation sites, the free energy of intermolecular bonding within the polymer, and two parameters that describe the free energy change as a function of size for the bonding of the heterogeneous nucleus to a polymer surface. This model provides an excellent fit to the data for B and B2A as a function of concentration using physically reasonable parameters. The model also correctly predicts the time regime in which stochastic behavior is observed for polymerization in small volumes.     

Kinetics of protein adsorption and desorption on surfaces with grafted polymers

The kinetics of protein adsorption are studied using a generalized diffusion approach which shows that the time-determining step in the adsorption is the crossing of the kinetic barrier presented by the polymers and already adsorbed proteins. The potential of mean-force between the adsorbing protein and the polymer-protein surface changes as a function of time due to the deformation of the polymer layers as the proteins adsorb. Furthermore, the range and strength of the repulsive interaction felt by the approaching proteins increases with grafted polymer molecular weight and surface coverage. The effect of molecular weight on the kinetics is very complex and different than its role on the equilibrium adsorption isotherms. The very large kinetic barriers make the timescale for the adsorption process very long and the computational effort increases with time, thus, an approximate kinetic approach is developed. The kinetic theory is based on the knowledge that the time-determining step is crossing the potential-of-mean-force barrier. Kinetic equations for two states (adsorbed and bulk) are written where the kinetic coefficients are the product of the Boltzmann factor for the free energy of adsorption (desorption) multiplied by a preexponential factor determined from a Kramers-like theory. The predictions from the kinetic approach are in excellent quantitative agreement with the full diffusion equation solutions demonstrating that the two most important physical processes are the crossing of the barrier and the changes in the barrier with time due to the deformation of the polymer layer as the proteins adsorb/desorb. The kinetic coefficients can be calculated a priori allowing for systematic calculations over very long timescales. It is found that, in many cases where the equilibrium adsorption shows a finite value, the kinetics of the process is so slow that the experimental system will show no adsorption. This effect is particularly important at high grafted polymer surface coverage. The construction of guidelines for molecular weight/surface coverage necessary for kinetic prevention of protein adsorption in a desired timescale is shown. The time-dependent desorption is also studied by modeling how adsorbed proteins leave the surface when in contact with a pure water solution. It is found that the kinetics of desorption are very slow and depend in a nonmonotonic way in the polymer chain length. When the polymer layer thickness is shorter than the size of the protein, increasing polymer chain length, at fixed surface coverage, makes the desorption process faster. For polymer layers with thickness larger than the protein size, increases in molecular weight results in a longer time for desorption. This is due to the grafted polymers trapping the adsorbed proteins and slowing down the desorption process. These results offer a possible explanation to some experimental data on adsorption. Limitations and extension of the developed approaches for practical applications are discussed.     

Isotherm,kinetic, and thermodynamic studies on the adsorption behavior of 10-deacetylpaclitaxel onto Sylopute

The adsorption of 10-deacetylpaclitaxel onto Sylopute was investigated at different initial 10-DAP concentrations, adsorption temperatures, and durations. The Freundlich isotherm model showed good fit to the equilibrium adsorption data. It was found that adsorption capacity increases with increasing temperature and that the adsorption of 10-DAP onto Sylopute is favorable and physical in nature. The obtained kinetic data agree well with the pseudo-second-order model, and the adsorption reaches equilibrium very quickly within 1 min. Thermodynamic parameters revealed the endothermic, irreversible and nonspontaneous nature of adsorption. The isosteric heat of adsorption changes very little as the adsorption capacity increases.     

Cooperative polymerization reactions. Analytical approximations, numerical examples, and experimental strategy

How does one obtain kinetic rate constants from the time course of a reversible and cooperative polymerization reaction? We examine a simple version of the homogeneous nucleation-elongation model with both analytical and numerical techniques to test some common assumptions and develop an experimental strategy. The assumption of irreversible polymer formation is found to be a useful and adequate approximation for the numerical determination of monomer disappearance. The assumption of early "pre-equilibrium" between monomer and seed, however, is shown numerically and analytically to produce significant errors over a wide range of parameters, particularly for small seed lengths. We exhibit numerical solutions for many different parameters, and also discuss analytical techniques that allow approximate solutions for several conditions: the high-concentration limit; the long-time limit; and the long-seed-length, lows concentration limit. The overall reaction simplifies when the monomer concentration is large. An experimental strategy for elucidating the seed size and the rate constants for polymerization and depolymerization is presented.     

Surface plasmon resonance study of carbohydrate-carbohydrate interaction between various gangliosides and Gg3-carrying polystyrene

Carbohydrate-carbohydrate interactions between Gg3 trisaccharide-carrying polystyrene (PN(Gg3)) and monolayers of several glycosphingolipids (GSLs) were quantitatively investigated by surface plasmon resonance techniques. PN(Gg3) was adsorbed onto a GM3 monolayer strongly and specifically with an apparent affinity constant of K(a) = 2.5 x 10(6) M(-1), and the apparent affinity constants onto GSLs decreased in the following order: GM3 > LacCer > (KDN)GM3 approximately GlcCer > GM2 approximately GD3 approximately GM4 > GM1 approximately 2,6-isoGM3 > ceramide. These results suggest that PN(Gg3) recognizes not only some specified portions of GM3 but also the trisaccharide as a whole. On the other hand, PN(Lac) and PN(Cel) were bound to GSLs less strongly (K(a) approximately 10(4) M(-1)) and less selectively. The kinetic analysis revealed that the selectivity in the adsorption of PN(Gg3) onto the GM3 monolayer is dominated by the faster adsorption rate.     

Chiral imprinted polymers as enantiospecific coatings of stir bar sorptive extraction devices

This paper reports the design of Molecularly Imprinted Polymers (MIP) with affinity towards (S)-citalopram using computational modeling for the selection of functional monomers and monomer:template ratio. Acrylamide was selected as functional monomer and the final complex functional monomer/template resulted in a 3:1 ratio. The polymer was synthesized by radical polymerization initiated by UV onto magnetic stir-bars in order to obtain a stir bar sorptive extraction (SBSE) device capable of selective enantiomeric recognition. After successful template removal, the parameters affecting the SBSE procedure (sample volume, ionic strength, extraction time and pH) were optimized for the effective rebinding of the target analyte. The resultant chirally imprinted polymer based stir-bar was able to selectively extract (S)-citalopram from a racemic mixture in an aqueous media with high specificity (specificity factor 4) between 25 and 500 μgL(-1). The MIP coated stir-bars can have significance for enantiospecific sample pre-concentration and subsequent analysis without the need for any chiral chromatographic separation.     

Kinetics of adsorption of Zn(II) ion on chitosan derivatives

The adsorption of Zn(II) ions from aqueous solution by chitosan derivatives (KCTS and HKCTS) was studied in a batch adsorption system. The adsorption capacities and rates of Zn(II) ions onto chitosan derivatives were evaluated. The adsorption isothermal data could be well interpreted by the Langmuir and Freundlich models. The kinetic experimental data properly correlated with the second-order kinetic model, which indicates that the chemical adsorption is the rate-limiting step. The apparent adsorption activation energy were 25.47 kJ mol⁻ and 5.473 kJ mol⁻, respectively, and the second-order adsorption constant for KCTS and HKCTS were 0.00311 g (mg min)⁻¹ and 0.005 g (mg min)⁻¹, respectively.     

Biosorption of 2,4-dichlorophenol by immobilized white-rot fungus Phanerochaete chrysosporium from aqueous solutions

The fungus Phanerochaete chrysosporium was immobilized in several polymer matrices: Ca-alginate, Ca-alginate-polyvinyl alcohol (PVA) and pectin, and was then used as a biosorbent for removing 2,4-dichlorophenol (2,4-DCP) in wastewater. Immobilization of P. chrysosporium onto pectin was less efficient than that onto other matrices because of its poor mechanical strength and low adsorption efficiency. Ca-alginate immobilized fungal beads with biocompatibility exhibited good mechanical strength and adsorption efficiency over 60%. Among the different biomass dosages in Ca-alginate immobilized fungal beads, 1.25% (w/v) was the optimum. The adsorption data of 2,4-DCP on the blank Ca-alginate beads, free, and immobilized fungal biomass could be described by the Langmuir and Freundlich isotherms very well. Desorption operation was efficiently completed by using distilled water as eluant, and the desorption efficiency reached 82.16% at an optimum solid/liquid ratio of 14.3. The consecutive adsorption/desorption cycles studies employing the Ca-alginate immobilized fungal beads demonstrated that the immobilized fungal biomass could be reused in five cycles without significant loss of adsorption efficiency and adsorbent weight.     

Adsorptive features of acid-treated olive stones for drin pesticides: Equilibrium,kinetic and thermodynamic modeling studies

The adsorption behavior of drin pesticides from aqueous solution onto acid treated olive stones (ATOS) was investigated using stir bar sorptive extraction and gas chromatography coupled with mass spectroscopy. The effects of sorbent particle size, adsorbent dose, contact time, concentration of pesticide solution and temperature on the adsorption processes were systematically studied in batch shaking sorption experiments. Maximum removal efficiency (94.8%) was reached for aldrin (0.5 mg L⁻¹) using the fraction 63–100 μm of ATOS (solid/liquid ratio: 1 g L⁻¹). Experimental data were modeled by Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherms. The Freundlich isotherm model (R² = 0.98–0.99) fitted the equilibrium data better than the Langmuir and D–R isotherm models, with low sum of error values (SE = 1.4–9.2%). The mean adsorption free energy derived from the D–R isotherm model (R² = 0.95–0.99) showed that the adsorption of drin pesticides was taken place by weak physical forces, such as van der Waals forces and hydrogen bonding. The calculated thermodynamic parameters, ΔH, ΔS and ΔG prove that drin pesticides adsorption on ATOS was feasible, spontaneous and exothermic under examined conditions. The pseudo first order, pseudo second order kinetic and the intra-particle diffusion models were used to describe the kinetic data and rate constants were evaluated.     

Basic dye adsorption onto an agro-based waste material--sesame hull (Sesamum indicum L.)

The aim of this project was to establish an economical and environmentally benign biotechnology for removing methylene blue (MB) from wastewater. The adsorption process of MB onto abandoned sesame hull (Sesamum indicum L.) (SH) was investigated in a batch system. The results showed that a wide range of pH (3.54-10.50) was favorable for the adsorption of MB onto SH. The Langmuir model displayed the best fit for the isothermal data. The exothermic adsorption process fits a pseudo-second-order kinetic model. The maximum monolayer adsorption capacity (359.88 mg g(-1)) was higher than most previously investigated low-cost bioadsorbents (e.g., peanut hull, wheat straw, etc.). This study indicated that sesame hull is a promising, unconventional, affordable and environmentally friendly bio-measure that is easily deployed for removing high levels of MB from wastewater.