Adsorber, solid, competitive

Various functional forms for / have been proposed either as a result of empirical observation or in terms of specific models. A particularly important example of the latter is that known as the Langmuir adsorption equation [2]. By analogy with the derivation for gas adsorption (see Section XVII-3), the Langmuir model assumes the surface to consist of adsorption sites, each having an area a. All adsorbed species interact only with a site and not with each other, and adsorption is thus limited to a monolayer. Related lattice models reduce to the Langmuir model under these assumptions [3,4]. In the case of adsorption from solution, however, it seems more plausible to consider an alternative phrasing of the model. Adsorption is still limited to a monolayer, but this layer is now regarded as an ideal two-dimensional solution of equal-size solute and solvent molecules of area a. Thus lateral interactions, absent in the site picture, cancel out in the ideal solution however, in the first version is a properly of the solid lattice, while in the second it is a properly of the adsorbed species. Both models attribute differences in adsorption behavior entirely to differences in adsorbate-solid interactions. Both present adsorption as a competition between solute and solvent. 

Competition between liquid mobile phase and solid adsorbent 1 Competition between liquid mobile phase and liquid stationary phase 1 Molecular sieving 1 Lock and Key mechanism 1 Competition between liquid mobile phase and ionic stationary phase... 

Basically the experimental parameters affecting the sorption behavior in simple systems (concentration of the adsorbate, solid to liquid ratio, equilibration time, temperature, pH, and ionic strength) are also important in sorption competition. Thus, Table 4.7 has the same columns as Tables 4.1 and 4.2 (specific adsorption in absence of competitors). In simple systems little attention is usually paid to the sequence of addition of reagents, but in studies of sorption competition this factor must not be neglected. The fact that some adsorbate is added (brought in contact with the adsorbent) first makes it a more successful competitor. Let us consider the following experiment. The adsorbent is equilibrated with solution of adsorbate I (adsorbate of interest), then the adsorbent is separated from the solution and contacted with solution of adsorbate 2 (competitor), and then the concentration of adsorbate 1 in solution is determined after certain equilibration time. Only a fraction of adsorbate 1 is released even if adsorbate 2 is a very strong competitor. However, adsorbate 2 added first or simultaneously with adsorbate I would completely prevent sorption of adsorbate 1 at otherwise identical experimental conditions. 

Nelson et al(28) have developed an equation assuming competitive equilibrium between Pu(IV) and soluble complexing ligands and between Pu(IV) and a solid adsorber ... 

Another commonly used ELISA format is the immobilized antibody assay or direct competitive assay (Eigure 3). The primary anti-analyte antibody is immobilized on the solid phase and the analyte competes with a known amount of enzyme-labeled hapten for binding sites on the immobilized antibody. Eirst, the anti-analyte antibody is adsorbed on the microtiter plate wells. In the competition step, the analyte and enzyme-labeled hapten are added to microtiter plate wells and unbound materials are subsequently washed out. The enzyme substrate is then added for color production. Similarly to indirect competitive immunoassay, absorption is inversely proportional to the concentration of analyte. The direct competitive ELISA format is commonly used in commercial immunoassay test kits. 

Competition between liquid mobile phase and solid adsorbent... 

It is incorrect to assume that adsorption always represents a decrease in system entropy. Adsorption at the solid surface by a solute component may require the removal of another species which is adsorbed to the surface, hence the increased order or disorder of the system accompanying competitive adsorption from solution is not so clear cut as might be the case of adsorption of a gas molecule from a near-vacuum. 

Coadsorption, in which two different kinds of particles are chemisorbed on the solid surface, may be classified into cooperative adsorption and competitive adsorption. Cooperative adsorption takes place with two different adsorbate particles of opposite characteristics, such as electron-donating particles and electron-accepting particles (e.g. Na and S), and the two adsorbate particles are adsorbed uniformly on the solid surface. On the other hand, competitive adsorption involves two different particles of similar characteristics, i.e. both being electron-donating or electron-accepting particles (e.g. O and S), which are adsorbed separately on the solid surface. 

O2 species formed over LaFeo SCU0.2O3 after O2 adsorption were investigated via O2-TPD experiments as described in Table 9, showing a-02 peaks at 253 and 671 °C and P-O2 peak at 793 °C. In the presence of 20 ppm SO2 in the adsorption gas, a diminution of adsorbed O2 species (especially ai-02) formed over LaFeo 8CU0 2O3 was found (see Table 9), indicating a competitive adsorption between gaseous SO2 and O2 at the same site. Acidic SO2 was believed preferentially adsorbed on the surface of perovskite compared to O2 due to the basicity of this solid. A process similar to a-02 adsorption upon anion vacancies is involved ... 

If any of the products of the reaction are themselves adsorbed strongly enough to occupy an appreciable fraction of the surface, less space becomes available for the reacting molecules, and the rate of transformation is proportionately diminished. There is now a competition, for places on the surface of the solid, between the molecules of the reactant and those of the product. In the general case this leads to a rather complicated equation for the progress of the reaction. 

Abstract Unsteady liquid flow and chemical reaction characterize hydrodynamic dispersion in soils and other porous materials and flow equations are complicated by the need to account for advection of the solute with the water, and competitive adsorption of solute components. Advection of the water and adsorbed species with the solid phase in swelling systems is an additional complication. Computers facilitate solution of these equations but it is often physically more revealing when we discriminate between flow of the solute with and relative to, the water and the flow of solution with and relative to, the solid phase. Spacelike coordinates that satisfy material balance of the water, or of the solid, achieve this separation. Advection terms are implicit in the space-like coordinate and the flow equations are focused on solute movement relative to the water and water relative to soil solid. This paper illustrates some of these issues. 

Fundamental studies on the adsorption of supercritical fluids at the gas-solid interface are rarely cited in the supercritical fluid extraction literature. This is most unfortunate since equilibrium shifts induced by gas phase non-ideality in multiphase systems can rarely be totally attributed to solute solubility in the supercritical fluid phase. The partitioning of an adsorbed specie between the interface and gaseous phase can be governed by a complex array of molecular interactions which depend on the relative intensity of the adsorbate-adsorbent interactions, adsorbate-adsorbate association, the sorption of the supercritical fluid at the solid interface, and the solubility of the sorbate in the critical fluid. As we shall demonstrate, competitive adsorption between the sorbate and the supercritical fluid at the gas-solid interface is a significant mechanism which should be considered in the proper design of adsorption/desorption methods which incorporate dense gases as one of the active phases. 

Adsorption chromatography The process can be considered as a competition between the solute and solvent molecules for adsorption sites on the solid surface of adsorbent to effect separation. In normal phase or liquid-solid chromatography, relatively nonpolar organic eluents are used with the polar adsorbent to separate solutes in order of increasing polarity. In reverse-phase chromatography, solute retention is mainly due to hydrophobic interactions between the solutes and the hydrophobic surface of adsorbent. Polar mobile phase is used to elute solutes in order of decreasing polarity. 

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