Competitive Adsorption Kinetics Research Articles

Adsorption equilibrium and kinetic study of guaifenesin enantiomers on cellulose tris 3,5-dimethylphenylcarbamate packed column

The chromatographic separation of guaifenesin enantiomers using hexanes/ethanol mobile phase and cellulose tris 3,5-dimethylphenylcarbamate stationary phase (Chiralcel OD) was investigated, where the column was packed with particle size 20μm of chiral adsorbents. The adsorption equilibrium isotherms of single enantiomer and racemic compounds of guaifenesin on Chiralcel OD stationary phase were measured by the frontal analysis and the adsorption–desorption method, respectively. Then, the experimental data were fitted with the Linear+Langmuir isotherm model, and the relative model parameters for the competitive adsorption equilibrium isotherm of guaifenesin enantiomers were obtained by the nonlinear regression method. Both the elution and adsorption–desorption experiments for the separation of guaifenesin enantiomers on the Chiralcel OD packed column were carried out. The measured elution curves and adsorption–desorption profiles were compared with the theoretical predictions by mathematical model, and adsorption kinetics, separation efficiency, the effect of dead volume were discussed. According to experiments and modeling, the competitive adsorption equilibrium and kinetics information were acquired for the scale up and optimization of the separation of guaifenesin enantiomers by both batch and continuous chromatographic system.

Separation of tungsten and molybdenum using macroporous resin: Competitive adsorption kinetics in binary system

The method using macroporous resin has great potential in separating mixed solution containing a high concentration of both W and Mo. The competitive adsorption kinetics of W and Mo onto the macroporous weak base resin D301 was studied in the present work. Accordingly, the effect of several factors such as concentration, particle size and temperature was assessed on the adsorption kinetics and separation of these two metals. Back-scattering SEM and EDS line scan were performed to study the competitive adsorption behavior of W and Mo, particularly. The macroporous resin D301 exhibits a better selectivity towards W than Mo in the near-neutral solution. The decrease of resin particle size and the increase of temperature are found to increase the adsorption rate and reduce the time required for obtaining the optimum separation results. Furthermore, the adsorption kinetics of W can be expressed by the pseudo-second order model. Such model was successfully modified to describe the Mo adsorption kinetics which is significantly affected by W polyions. Diffusion process was identified as the mechanism controlling the rate of W and Mo adsorption.

Removal of radioactive iodine from water using Ag2O grafted titanate nanolamina as efficient adsorbent

Emergency treatment of radioactive material leakage and safety disposal of nuclear waste is a constant concern all along with the development of radioactive materials applications. To provide a solution, titanate with large surface area (143m2g−1) and a lamina morphology (the thickness of the lamina is in range of tens of nanometers) was prepared from inorganic titanium compounds by hydrothermal reactions at 433K. Ag2O nanocrystals (5–30nm) were deposited onto the titanate lamina. The surface of the titanate lamina has crystallographic similarity to that of Ag2O nanocrystals. Hence, the deposited Ag2O nanocrystals and titanate substrate join together at these surfaces, forming a well-matched phase coherent interface between them. Such coherence between the two phases reduces the overall energy by minimizing surface energy and anchors the Ag2O nanocrystals firmly on the external surface of the titanate structure. The composite thus obtained was applied as efficient adsorbent to remove radioactive iodine from water (one gram adsorbent can capture up to 3.4mmol of I− anions). The composite adsorbent can be recovered easily for safe disposal. The structure changes of the titanate lamina and the composite adsorbent were monitored by various techniques. The isotherm and kinetics of iodine adsorption, competitive adsorption and column adsorption using the adsorbent were studied to assess its iodine removal abilities. The adsorbent exhibited a capacity as high as 3.4mmol of iodine per gram of adsorbent in 1h. Therefore, Ag2O deposited titanate lamina is an effective adsorbent for removing radioactive iodine from water.

Kinetics of Competitive Adsorption of β-Casein and Methylene Blue on Hydrophilic Glass

The competitive adsorption of methylene blue (MB) and β-casein on hydrophilic glass from an aqueous mixed solution was directly detected at the solution pH smaller than the protein isoelectric point (pI) by means of the waveguide-based broadband time-resolved evanescent wave absorption spectroscopy. The competitive adsorption causes the MB coverage to exponentially decrease with time from its peak value and prevents MB aggregation at the interface. The kinetic equation for the competitive adsorption of binary adsorbates was theoretically deduced based on the Langmuir model, and was used for creating the best fit to the experimental data. In the case of a fixed concentration of MB in the mixed solution, the best-fit parameter τ(-1) increases with the protein concentration at a specific pH and decreases with the solution pH at a given concentration of protein. The findings suggest that the β-casein concentration in sub-μM level can be rapidly determined by the time-resolved waveguide absorptiometry based on the competitive adsorption of MB and protein.

Competitive Adsorption between Polyethylene Glycol and Acid Brilliant Red on Expanded Graphite

Expanded graphite (EG) adsorbent was prepared with graphite as raw materials, potassium permanganate as oxidant, and vitriol as intercalation compound. Polyethylene glycol (PEG) 10000 and Acid brilliant red 3B (ABR) with obvious difference in molecular weights were selected as organic adsorbates, and their adsorption and competitive adsorption thermodynamics and kinetics on EG were investigated. The results are: In both single component system and dual component system, the adsorption and competitive adsorption isotherm of PEG 10000 and ABR on EG are all type I. In dual component system, the existence of another component would decrease the single component adsorbance, which might be caused by the competitive adsorption of these adsorbates for the same adsorbing site on EG. Adsorption and competitive adsorption are spontaneous, and the increase of ionic strength, temperature and expanded volume of the adsorbent would cause the increase of adsorbance. No matter the single component system or the dual component system, the adsorption kinetics models can all be well described with pseudo second-order model. Adsorption rate increases with the increase of temperature. Physical adsorption is the main action between EG with these adsorbates.

Competitive Adsorption of Thiolated Polyethylene Glycol and Mercaptopropionic Acid on Gold Nanoparticles Measured by Physical Characterization Methods

Competitive adsorption kinetics between thiolated polyethylene glycol (SH-PEG) and mercaptopropionic acid (MPA) on gold nanoparticles (Au-NPs) were studied using a prototype physical characterization approach that combines dynamic light scattering (DLS) and electrospray differential mobility analysis (ES-DMA). The change in hydrodynamic particle size (intensity average) due to the formation of SH-PEG coatings on Au-NPs was measured by DLS in both two-component (Au-NP + MPA or Au-NP + SH-PEG) and three-component (Au-NP +MPA + SH-PEG) systems. ES-DMA was employed to quantify the surface coverage of SH-PEG and establish a correlation between surface coverage and the change in particle size measured by DLS. A change in the equilibrium binding constant for SH-PEG on Au-NPs at various concentrations of SH-PEG and MPA showed that the presence of MPA reduced the binding affinity of SH-PEG to the Au-NP surface. Kinetic studies showed that SH-PEG was desorbed from the Au-NP surface following a second-order desorption model after subsequently introducing MPA. The desorption rate constant of SH-PEG from the Au-NP surface by MPA displacement was strongly affected by the concentration of MPA and the excess SH-PEG in solution.

Experimental and kinetic modeling of As(V) and As(III) adsorption on treated laterite using synthetic and contaminated groundwater: Effects of phosphate, silicate and carbonate ions

An efficient porous adsorbent for arsenic is developed from abundantly available laterite using an optimized acid followed by base treatment methodology. XRD, HRTEM, surface area analyzer and FTIR are used to characterize the treated laterite (TL). Arsenic adsorption capacity of TL is evaluated under varying process conditions in batch mode using synthetic solution of single arsenic species, mixture of both As(III) and As(V) species and real arsenic contaminated groundwater (CGW). The effects of competitive ions like phosphate, silicate, carbonate, etc., on arsenic adsorption using TL are explored in details. Langmuir isotherm is found to be a better fit of the experimental isotherm data of arsenic/TL system. The Langmuir maximum adsorption capacity and constant related to adsorption energy for As(V) and As(III) on TL are found to be 21.6±0.8mg/g, 20.6±0.5L/mg and 9.4±0.4mg/g, 5.0±0.1L/mg, respectively. The competitive adsorption kinetics of individual arsenic species on TL using mixed arsenic spiked water and CGW are studied by speciation technique. Shrinking core model is applied to match the predicted bulk concentration profile of arsenic with experimental data. The model is applied to evaluate the effective pore diffusivity (De) and external mass transfer coefficient (Kf) of arsenic for arsenic/TL system and these values are in the range of 1.3–1.6×10−9m2/s and 0.076–11.25×10−4m/s, respectively. Fixed bed column runs using 6.5cm TL bed (empty bed contact time: 2.92min) is capable to produce ∼3000 bed volume (96.7L, 1 bed volume=32.23mL) of water for effluent concentration at <10μg/L (initial arsenic concentration in CGW: 385±25μg/L). The study reveals that TL is porous and highly efficient adsorbent for both arsenic species.

Statistical Rate Theory Approach to Kinetics of Competitive Adsorption at the Solid/Solution Interface

Removal of pollutants from aqueous solution is an important process, and adsorption is one of the most popular methods for this. Wastewater usually contains several solutes, and therefore the adsorption process in some systems is competitive. The lack of an adequate model for kinetics of competitive adsorption and also difficulties in modeling led only to the reporting of experimental data in most publications. Here we propose the first description of the competitive adsorption kinetics at the solid/solution interface based on the statistical rate theory (SRT) approach. For derivation of rate equations based on the SRT approach, at first we derived the chemical potential of adspecies for a competitive adsorption based on statistical thermodynamics from the partition function of a canonical ensemble. The derived kinetic equations for competitive adsorption are able to describe quantitatively the kinetics of some experimental data. Since the analytical solution of the derived rate equations led to complex expressions, we used stochastic numerical simulation for modeling of experimental data by the derived SRT equations. The present study shows that the stochastic numerical simulation is a powerful technique for modeling adsorption kinetics based on statistical rate theory.

Interaction of formic and acetic acid with ice surfaces between 187 and 227 K. Investigation of single species- and competitive adsorption

The physical adsorption of formic (HC(O)OH) and acetic (CH(3)C(O)OH) acid on ice was measured as a function of concentration and temperature. At low concentrations, the gas-ice interaction could be analysed by applying Langmuir adsorption isotherms to determine temperature dependent partition constants, K(Lang). Using temperature independent saturation coverages (N(max)) of (2.2 +/- 0.5) x 10(14) molecule cm(-2) and (2.4 +/- 0.6) x 10(14) molecule cm(-2) for HC(O)OH and CH(3)C(O)OH, respectively, we derive K(Lang)(HC(O)OH) = 1.54 x 10(-24) exp (6150/T) and K(Lang)(CH(3)C(O)OH) = 6.55 x 10(-25) exp (6610/T) cm(3) molecule(-1). Via a van't Hoff analysis, adsorption enthalpies were obtained for HC(O)OH and CH(3)C(O)OH. Experiments in which both acids or HC(O)OH and methanol interacted with the ice surface simultaneously were adequately described by competitive adsorption kinetics. The results are compared to previous measurements and used to calculate the equilibrium partitioning of these trace gases to ice surfaces under conditions relevant to the atmosphere.

Coupled diffusion and adsorption effects for multiple proteins in agarose gel

AbstractA mathematical model for the hindered diffusion and competitive adsorption of two proteins in an agarose gel has been developed. In a simulation program the model has been used to study the competing and displacement effects on a single bead for lysozyme and bovine serum albumin (BSA) bound to the ligand Cibacron Blue in agarose gel. The model takes into account hindered diffusion described by the Renkin model, competitive Langmuir adsorption kinetics, pore size distribution of the gel, and a shrinking effective pore radius attributed to molecule‐to‐ligand binding. The simulation model can easily explain displacement of BSA or lysozyme dependent on the binding capacity, kinetics, and diffusion. The influence of a bimodal pore size distribution is demonstrated. It also provides insight into the phenomenon of static vs. dynamic binding capacity observed in experimental determinations of the isotherm. © 2004 American Institute of Chemical Engineers AIChE J, 50: 3006–3018, 2004

Competitive random sequential adsorption of point and fixed-sized particles: analytical results

We study the kinetics of competitive random sequential adsorption (RSA) of particles of binary mixture of points and fixed-sized particles within the mean-field approach. The present work is a generalization of the random car parking problem in the sense that it considers the case when either a car of fixed size is parked with probability q or the parking space is partitioned into two smaller spaces with probability (1-q) at each time event. This allows an interesting interplay between the classical RSA problem at one extreme (q=1), and the kinetics of fragmentation processes at the other extreme (q=0). We present exact analytical results for coverage for a whole range of q values, and physical explanations are given for different aspects of the problem. In addition, a comprehensive account of the scaling theory, emphasizing on dimensional analysis, is presented, and the exact expression for the scaling function and exponents are obtained.

Singularity of Polystyrene Chains as the Hydrophobic Group of Amphiphilic Copolymers in Competitive Adsorption Processes: A Comparative Study of Polystyrene−Poly(ethylene oxide) and Poly(dimethyl siloxane)−Poly(ethylene oxide) Block Copolymers

Competitive adsorption kinetics of three diblock copolymers, a poly(dimethyl siloxane)-poly(ethylene oxide) and two polystyrene-poly(ethylene oxide), at a hydrophobic solid-oil−water interface are investigated, under a nonuniform distribution of the copolymer in the aqueous phase. When exposed to a variable concentration profile of the copolymer, the solid-oil−water interface evolves through a time-dependent shape reconformation of the captive oil drop, which, for the two copolymers, reveals some strong qualitative differences. While the poly(dimethyl siloxane)-poly(ethylene oxide) adsorption results in a monotonically or stepwise shrinking of the captive drop in the whole range of the kinetics, the two polystyrene compounds exhibit a autophobic-like transition (early spreading/late stage shrinking). Based on the similarity in the number fraction of ethylene oxide units in the poly(dimethyl siloxane)-poly(ethylene oxide) and one of the polystyrene compounds, this adsorption induced wetting singularity is ...

Kinetics of Competitive Adsorption of PEO Chains with Different Molecular Weights

Molecular weight driven competitive adsorption of PEO [poly(ethylene oxide)] from aqueous solutions on silica was studied by employing total internal reflectance fluorescence (TIRF) and near-Brewster angle reflectivity. Coumarin tags on PEO chain ends facilitated the distinction between two competing populations differing only in molecular weight. In gentle shearing flow, coadsorption was found to include three steps: independent transport-limited adsorption of both species, exchange of short and long chains, and the ultimate equilibration of the long chains. When the short chains are on the order of 30K and contact the surface for 20 min or less, their displacement by longer chains is transport-limited and approaches completion. However, for short chains of higher MW (120K), their displacement by longer chains becomes slow and less complete, indicating an energy barrier for short chain displacement. A kinetic model for competitive adsorption kinetics was proposed on the basis of the Langmuir adsorption ...

Adsorption and Desorption Kinetics of Mixtures on Planar Surfaces under Flow Conditions

The adsorption isotherms and the adsorption/desorption kinetics of a mixture of nonionic water-soluble associative polymers with different molecular weights on silicon wafers and polystyrene films under flow conditions were studied. Equations were derived to calculate the parameters characterizing the kinetic-diffusive-convective-controlled adsorption and desorption processes under flow conditions: (a) the equilibrium adsorption, (b) the thickness of the adsorbed layer, (c) the activation energy of adsorption, (d) the rate constant, (e) the effective coefficients of diffusion in the adsorbed layer, and (f) the time needed to attain the equilibrium state for the adsorption and desorption processes for individual components and mixtures. We also studied the competitive adsorption kinetics of water-soluble nonionic polyurethane polymer based on poly(ethylene glycol), with an average molecular weight of 12 000, 62 000, and 120 000 g/mol and with a C16H33 linear alkyl group on each end of the molecule, from aqueous solution onto the silica (SiO2) and polystyrene films by ellipsometry.

Competitive adsorption of human serum albumin and gamma-globulin from a binary protein mixture onto hexadecyltrichlorosilane coated glass

The kinetics of competitive adsorption of proteins onto hexadecyltrichlorosilane coated glass (HTS-glass) from model solutions containing fluorescein isothiocyanate (FITC)-labeled human serum albumin (HSA-FITC) and gamma-globulin (HGG-FITC) were studied by total internal reflection fluorescence (TIRF) spectroscopy. The processes of displacement of HSA-FITC by HGG are independent of the conformational state of HSA adsorbed onto glass. On HTS-glass, displacement of protein is hindered by the presence of large numbers of CH3-terminated alkyl tails which induce conformational (reorientational) changes in HSA-FITC and HGG-FITC adsorbed from simple solutions. In contrast to HSA, adsorption of HGG onto HTS-glass from a simple solution is characterized by the absence of irreversible adsorption in the initial portion of the kinetic curve. Competition between HSA and HGG-FITC induces replacement of end-on adsorbed HGG-FITC on HTS-glass surface with subsequent desorption of the HGG-FITC into solution. Upon further increase in the HSA concentration in solution the competition of HSA for adsorption sites prevails, which leads to a decrease in the amount of adsorbed HGG-FITC and, consequently, to a decrease in the rate of its displacement.

Mathematical Models of Polymer Adsorption at a Porous Adsorbent Surface

Mathematical models describing kinetics of adsorption and competitive adsorption of polymers into porous media have been developed. The models predict the constant of adsorption equilibrium, the rate constants of adsorption, of desorption, and of substitution of small polymer chains by large ones, and the maximum amount of polymer that can be adsorbed on a unit area of the surface. Using experimental adsorption data of monodisperse polystyrenes and porous silica, we show that there is good agreement between the kinetic models and the experimental data.

A Comprehensive Model of Multiprotein Adsorption on Surfaces

A mathematical model for protein adsorption from solution to surfaces was developed and a numerical solution was obtained. The model proposes a reaction-diffusion mechanism for multiple proteins, involving interactions between diffusive-convective protein transport from the bulk solution and competitive adsorption and displacement kinetics on the surface. The resulting equations in time and space were solved numerically with a finite difference approach. Using a simulated dilute plasma solution consisting of albumin, immunoglobulin-γ, and fibrinogen at their physiological proportions, the phenomenon of sequential protein adsorption and displacement oil the surface (known as the Vroman effect), was shown. Explanations were obtained for several other phenomena observed by biomaterials researchers studying protein adsorption. The model also allows the study of how the modification of surface parameters can determine adsorption behavior. This study not only demonstrates the complexity of the adsorption process but also shows that it can be quantified by comprehensive models.

Competitive Adsorption Kinetics of Polymers Differing in Length Only

Optical reflectometry was used to monitor adsorbed amounts of homopolymer as a function of time, and an impinging jet flow cell was used to control mass-transfer rates between the solution and the adsorbing surface. For poly(ethylene oxide) (PEO) adsorbing from water onto silica we found that exchange of short adsorbed polymers against longer ones in solution takes place at constant coverage, the total adsorbed amount being equal to the saturated level of the short component. This result agrees fully with predictions for an adsorbed layer of mixed composition which is in full equilibrium with its immediate surroundings

Kinetics of competitive adsorption of polystyrene chains at a porous silica surface

Kinetics of competitive adsorption of polystyrene chains at a porous silica surface

Competitive adsorption kinetics of end-adsorbing polymers

The kinetics and equilibrium of adsorption of two competing species of end-adsorbing polymer chains are considered as a model system for study of competitive adsorption processes in commercially relevant colloidal stabilizers. Two typical situations are considered invasion of an existing layer by shorter chains with a similar end group, and invasion by chains of the same length with a more strongly-adsorbing end group. It is shown that the short-chain invaders readily adsorb in the presence of an existing layer and lead to enhanced desorption of the original chains. Invading chains with stronger stickers are not effective in quickly displacing the original layer.