Studies of competitive adsorption

Horne, D.S., Atkinson, P.J., Dickinson, E., Pinfield, V.J., Richardson, R.M. (1998). Neutron reflectivity study of competitive adsorption of p-lactoglobulin and non-ionic surfactant at the air-water interface. International Dairy Journal, 8, 73-77. 

In studies of competitive adsorption, the usually measured quantity is the overall composition of the adsorbed phase for a given composition of the bulk phase in equilibrium with it. It has been found that chemical shifts can provide a more detailed description. In a mixture of Xe and Kr in N 4 zeolite it was possible to observe the individual signals from XenKr mixed clusters as well as the Xen clusters under magic angle spinning (28). The absolute 129Xe chemical shifts of the XenKr mixed clusters and the increments between XenKr and the Xen+1 in various Xe-Kr mixtures in Na4 zeolite, are shown in Table I. 

Our studies (19) indicated that proteins were readily adsorbed from aqueous solution onto hydrophobic polymer surfaces with Langmuir type adsorption and that the rate of adsorption toward a plateau surface concentration depends on the polymer nature. In the study of competitive adsorption from a protein mixture solution (20), fibrinogen and y-globulin adsorb onto FEP very rapidly compared with PEUU and SR. Therefore, the FEP surface in contact with blood has more acceptor sites for platelet adhesion than does the PEUU or SR surface. 

Pelekani, C. and Snoeyink V.L. (2001). A kinetic and equihbrium study of competitive adsorption between atrazine and Congo Red dye on activated carbon the importance of pore size distribution. Carbon, 39(1), 25-37. 

In order to approach more closely to the blood system itself and to determine the influence of other proteins on fibrinogen adsorption, we undertook studies of competitive adsorption between fibrinogen and other plasma proteins. In these studies, etimes the adsorption of only fibrinogen (labelled with I) was followed sometimes that of both fibrinogen and a second protein (labelled with I) were followed. 

The QELS and adsorption studies of competitive adsorption and aggregation of macromolecules/ NP for polymers (PVP, PEG, PVA), gelatin, ovalbumin or BSA, and nanosilica are in agreement with the QCM data with respect to the effects of surface roughness, confinement space in pores, and the characteristics of macromolecules and their interactions in pre-adsorbed macromolecules and with partially coated solid surfaces. Proteins can more effectively displace smaller polymer molecules if the latter have only electron-donor groups (PEG, PVP). In the case of a pre-adsorbed... 

Finally, research trends on this topic include the study of competitive adsorption, for instance, between NOM and micro-pollutants such as pesticides adsorption of bacteria which in turn can catalyze the decomposition of the adsorptive adsorption/desorption of drugs for medical applications and modifications of the adsorptive depending on the solution and carbon surface chemistry. 

Dimension of constants k1 is (mole X 102 hr-Ikg-Iatm-2) and of adsorption coefficients K, is (atm-1)-b From the study of competitive system (Villa). 

Although there have been several studies of chemisorption of certain molecules of interest, there are fewer studies of co-adsorption. This possibly arises from the increasing complexities of controlling coverage in situations where competitive adsorption may exclude or alter the coverage of the reactants. The goal of co-adsorption studies is to learn about interactions between surface coadsorbates, a subject of obvious importance to their catalytic reaction. It is especially of interest from the view of emission control catalysis to study coadsorption of an oxidant and a reductant. 

In a study of selective adsorption of sulfur compounds and aromatic compounds in a hexadecane on commercial zeolites, NaY, USy, HY, and 13X by adsorption at 55 °C and flow calorimetry techniques at 30 °C, Ng et al. found that a linear correlation between the heat of adsorption and the amount of S adsorbed for NaY.162 Competitive adsorption using a mixture of anthracene, DBT, and quinoline indicates that NaY selectively adsorbs quinoline, while anthracene and DBT have similar affinity to NaY, indicating that NaY is difficult to adsorptively separate sulfur compounds from aromatic hydrocarbons with the same number of the aromatic rings. 

The idea of competitive adsorption on pair-sites has also been used to describe the interaction of Ho and H2O with magnetite ( ). When isotherms were collected using M2/H2O mixtures following the same approach as discussed above, it was found that the data fit a model where H2 adsorbed dissociatively and H2O adsorbed associative-ly, with both species competing for pair-sites. These studies were conducted at water-gas shift reaction temperatures (e.g., 650 K) and as for the adsorption of CO and CO2, only a fraction of the magnetite surface was capable of adsorbing H2 and H2O. 

However, when considering uranium transport at the same site, we need to consider a different set of chemical reactions. Uranium is a trace component in groundwater. The consideration of the interactions between the chemical components, both in the aqueous phases and between the aqueous and solid phases, is different from sulfate, the major component. Uranium transport is most likely controlled by surface adsorption onto mineral surfaces. So the surface adsorption reactions that are safely ignored in the sulfate case are now important. Surface reactions concerning other trace metals, for example, Ni and Cd, are ignored in the sulfate transport case, but now they need to be included because of competitive adsorption. Furthermore, even though our concern is about a trace component, i.e., uranium, we need to know the major components of groundwater to study uranium transport because the iron oxide surface sites may be mostly occupied by sulfate at low / H. 

Studying the role of the nature and molecular structure of the adsorbing species, it should be taken into consideration that it is not possible to avoid the occurrence of simultaneous processes. Thus the result of an experimental work aimed at the study of the adsorption of a preselected species reflects the outcome of competitive processes. 

H NMR imaging has been used to study the diffusion of pure hydrocarbons (benzene, n-hexane,) during their adsorption in or desorption from a fixed bed of zeolite crystallites. This technique is used to visualize the progression of the diffusing molecules in the zeolite bed and to determine their intracrystallite diffusion coefficients. In the case of competitive adsorption, it gives the time dependence of the distribution of the two coadsorbed gases. 

Competitive Adsorption of Fibrinogen and Albumin. When a foreign surface contacts blood it encounters a complex mixture of plasma proteins. The adsorption rates and surface coverages determined for proteins individually will undoubtedly differ when several proteins challenge the surface simultaneously. Therefore, a study of the adsorption characteristics of multi-component protein solutions has been conducted using TIRF. When extrinsic labeling is employed, TIRF is particularly suitable for studying competitive adsorption. 

We begin with some comments on the various experimental methods used in our studies. Investigations of single proteins in buffer are then discussed, including kinetics and isotherms, reversibility, denaturation, and the structural status of adsorbed proteins. Results of competitive adsorption studies using mixtures of proteins in buffer are then described. We next discuss our more recent studies of protein adsorption from blood plasma using both radiolabeled proteins and elution techniques. Finally, data on the effect of red blood cells on protein adsorption are summarized. 

The experimental study of the adsorption of organic compounds on electrodes began in the first decade of the previous century with Gouy s electrocapillary work. Since then it has attracted considerable attention, mainly because it affects the mechanism of most of the processes occurring on electrodes. The first attempts to present a theoretical description of the effect of the electric field on adsorption appeared in 1925 and 1926 by Frumkin, who formulated the macroscopic model of condensers in parallel. The interpretation of the electrosorption of organic compounds at a molecular level was initiated by Butler" in 1929, but it was the work of Bockris and co-workers in 1963 that put the bases of the contemporary microscopic modelling. The main contribution by Bockris et al. was the introduction of the concept of the competition between solvent and adsorbate molecules for adsorption and the reorientation of the adsorbed molecules on the electrode upon the variation of the electric field. ... 

The adsorption of liquid mixtures leads to the study of competition for the adsorption sites. Goworek et al. [113] studied the adsorption of mixtures of hydrocarbons on a series of silica gels with different porosity. They foimd evidences that most of the systems included in their work tend to form mixed surface phases. They also conclude that excess adsorption and the observed selectivity depend on the pore size. 

Wang C, Groenzin H, Shultz MJ (2004) Direct observation of competitive adsorption between methanol and water on Ti02 an in situ sum-frequency generation study. J Am Chem Soc 126 8094-8095... 

A major stimulus to recent studies of physical adsorption on ionic crystals has been the desire to examine the fmstration resulting from the competition between the square symmetry of their (100) siuface and the natural hexagonal packing of the rare gases new universality classes could be accessible for the square two-dimensional lattice [64]. 

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