Kinetics of adsorption, desorption

Theoretical Approaches to the Kinetics of Adsorption, Desorption, and Reactions at Surfaces... 

If, on the timescale of observation, the degree of coverage of any site type becomes appreciable, the precise nature of the relationship between Fi, F2 and has to be taken into account. For the case of a Langmuirian isotherm (implying sufficiently fast kinetics of adsorption/desorption) this means that equations in (2) are applicable. Two particular cases are described here ... 

Due to the fast kinetics of adsorption/desorption reactions of inorganic ions at the oxide/aqueous interface, few mechanistic studies have been completed that allow a description of the elementary processes occurring (half lives < 1 sec). Over the past five years, relaxation techniques have been utilized in studying fast reactions taking place at electrified interfaces (1-7). In this paper we illustrate the type of information that can be obtained by the pressure-jump method, using as an example a study of Pb2+ adsorption/desorption at the goethite/water interface. 

Ketoglutaifo add, 283,286 Ketones, 275,298 Ketoprofen, 286 Kieselguhr, 117 Kihara potential, 206 Kinetic resistances, 227 Kinetics of adsorption-desorption, 10, 127, 159... 

The thermodynamics of adsorption of a given species are thus characterised by bifl and Ai/ads,i. By fitting the breakthrough curves, expressions for the kinetics of adsorption/desorption can be developed Fig. 27 shows simulated, as well as measured, breakthrough curves. 

Sorption to surfaces can have important effects on the rates of contaminant transformation, but these effects may be very different, depending on how the mechanism of sorption (i.e., hydrophobic partitioning, donor-acceptor interactions, or ligand exchange) relates to the mechanism of contaminant transformation (i.e., reaction in solution, reaction at surface sites, etc.). In general, however, the contributions of each compartment can be treated as additive as long as the kinetics of adsorption/desorption are fast, relative to contaminant transformation (168). Just as with the effect of pH (Section 4.2.3), each term is simply the product of the reactant concentrations in the compartment and the corresponding rate constant. 

Lindstrom, F. T., Haque, R., and Coshow, W. R. (1970). Adsorption from solution. III. A new model for the kinetics of adsorption-desorption processes. J. Phys. Chem. 74, 495-502. 

Mikami, N., Sasaki, M., Kikuchi, T., and Yasunaga, T. (1983b). Kinetics of adsorption-desorption of chromate on -y-Al203 surfaces using the pressure-jump technique. J. Phys. Chem. 87, 5245-5248. 

Analysis of results of experimental measurements of various parameters (isotherms and kinetics of adsorption/desorption, destruction charges, dynamics of percolation, etc.). 

Adsorption of carbon monoxide on platinum is not irreversible, since on switching carbon monoxide gas concentrations or with switching to pure hydrogen, the electrode potential rapidly relaxes and reverts to those values previously obtained for the absence of carbon monoxide. This shows that the kinetics of adsorption/desorption are rapid and reversible... 

Hachiya, K., M. Ashida, M. Sasaki, H. Kan, T. Inoue, and T. Yasunaga. 1979. Study of the kinetics of adsorption-desorption of lead(2+) ion on a gamma-aluminum oxide surface by means of relaxation techniques. J. Phys. Chem. 83 1866-1871. Heller-Kallai, L., and C. Mosser. 1995. Migration of Cu ions in Cu montmorillonite heated with and without alkali halides. Clays Clay Miner. 43 738-743. 

S.S. Dukhln, G. Kretzschmar and R. Miller, Dynamics of Adsorption at Liquid Interfaces, Elsevier (1995). (Although the emphasis is on the kinetics of adsorption, desorption and chemical reactions at interfaces, much information on the measurement and interpretation of interfacicil and surface tensions can be found.)... 

The third class involves electroactive adsorbed species, yet it also encompasses the case in which, although originally inactive, the species is activated or modified in the adsorption process to give rise to the formation of electroactive adsorbed molecules. Obviously, all these effects discussed for the two previous classes are observed for this class, but additional effects are observed for the adsorbed species itself. Indeed, adsorption modifies (1) the concentration of the species at the electrode surface vis-a-vis that predicted from its bulk concentration, and (2) the energetics of the electron transfer reaction. The latter point arises because of additional thermodynamic contributions to be considered in the Rq/Ro or Po/P equilibria in Scheme 5 and also from changes in the reorganization energies. The former point leads to a variety of behaviors, since it is obviously a function of the kinetics of adsorption-desorption phenomena. A third additional effect of electroactive adsorbed species arises from their possible ability to act as electron transfer med-... 

The sources of band broadening of kinetic origin include molecular diffusion, eddy diffusion, mass transfer resistances, and the finite rate of the kinetics of ad-sorption/desorption. In turn, the mass transfer resistances can be sorted out into several different contributions. First, the film mass transfer resistance takes place at the interface separating the stream of mobile phase percolating through the column bed and the mobile phase stagnant inside the pores of the particles. Second, the internal mass transfer resistance controls the rate of mass transfer between this interface and the adsorbent surface. It is composed of two contributions, the pore diffusion, which is molecular diffusion taking place in the tortuous, constricted network of pores, and surface diffusion, which takes place in the electric field at the liquid-solid interface [60]. All these mass transfer resistances, except the kinetics of adsorption-desorption, depend on the molecular diffusivity. Thus, it is important to study diffusion in bulk liquids and in porous media. 

As pointed out by Ruthven [3], the rates of adsorption and desorption in porous adsorbents are usually controlled by the rate of diffusion within the pore network, more than by the kinetics of adsorption-desorption. This is especially true in chromatography, where adsorbents are carefully prepared to exhibit only moderately strong energy of physisorption and no chemisorption. Thus, it is important to consider diffusion within the pore networks existing in the columns. 

Several phenomena affect the overall rate of the mass transfers in chromatography the mass transfer resistances from the percolating stream of the mobile phase to the mobile phase stagnant inside the pores of the particles, the dispersion through the porous particles, and the kinetics of adsorption-desorption. In... 

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