Fractional adsorption, defined

The adsorption force is proportional to the enthalpy of formation and varies considerably on the different surfaces of metal oxides. The enthalpy of adsorption is defined as the molar enthalpy when a molecule passes from the gaseous phase to the adsorbed state and can be adsorbed or dissociated. In this later case, we consider also the heat of dissociation. The heat of adsorption and dissociation depend on different factors, such as the surface, whether flat or irregular, and the fraction of... 

Alternatively, an integral distribution function F may be defined as giving the fraction of surface for which the adsorption energy is greater than or equal to a given Q,... 

FIGURE 3.5 Major components of classical receptor theory. Stimulus is the product of intrinsic efficacy (s), receptor number [R], and fractional occupancy as given by the Langmuir adsorption isotherm. A stimulus-response transduction function f translates this stimulus into tissue response. The curves defining receptor occupancy and response are translocated from each other by the stimulus-response function and intrinsic efficacy. 

As a second example, consider the partitioning of Cd(II) between two adsorbents—a-TiC and (am)Fe20j.H20. Figure 11 shows Cd(II) fractional adsorption as a function of pH for binary mixtures of these adsorbents under experimental conditions such that Cddl) and SOUp are constant only the surface site mole fraction varies from one end-member to the next. As the site mole fraction shifts between the end-members, the fractional adsorption edges for the binary adsorbent mixtures varies between the limits defined by end-members. In the absence of particle-particle interactions, the adsorbents should act as independent ligands competing for complexa-tion of Cd(II). If this is the case, then the distribution of Cd(II) in such binary mixtures can be described by a composite mass-action expression (13) which includes a separate term for the interaction of Cd(II) with each adsorbent. 

Adsorption to Mn oxides. The only thorough experimental study of Mo isotope fractionation to date focused on adsorption to Mn oxides (Barfing and Anbar 2004). The intent of this study was to examine the possibility that Mo isotopes are fractionated during this process. In these experiments. Mo dissolved in aqueous solution of defined iorfic strength at room temperature was exposed to synthetic 5-Mn02. pH (6.5-8.5) and solution-solid contact... 

As mentioned previously, the retention of contaminants on geosorbents may occur by surface adsorption on or into the coUoid fraction of the solid phase and by physical retention as hquid ganglia or as precipitates into the porous media. The type of retention is defined by the properties of the solid phase and the contaminants as well as by the composition of the subsurface water solution and the ambient temperature. 

Normally, catalytic activity is expressed as the reaction rate per unit area of active surface (expressed as metre per gram) under given conditions. In a chemical reaction, catalytic conversion is defined as the fraction of reactants converted to products and selectivity is a function of the rate of formation of a desired product with respect to the overall conversion of the initial reactants. The reactant molecules transfer to the catalyst surface where adsorption may occur on an active site , with possible rearrangement of their bonds leading to a chemical adsorption (chemisorption), gas-catalyst reaction and the subsequent desorption of new species. The active site or phase is of high activity and selectivity for the desired products. Thus, the nature of the active sites is important. In many cases, it is not enough to have just activity. Selectivity to desired products is important and often modifiers or promoters are needed both to improve the... 

This makes a convenient point of contact with theory since models for adsorption inevitably subdivide the surface into an array of adsorption sites that gradually fill as the pressure increases. If 6 is defined as the fraction of sites filled, then 6 = 1 corresponds to monolayer coverage, with 8 < 1 or 6 > 1 to submonolayer and multilayer coverages, respectively. Theoretical isotherms predict how 6 varies with p in terms of some particular model for adsorption. It turns out that a set of experimental points can often be fitted by more than one theoretical isotherm, at least over part of the range of the data that is, theoretical isotherms are not highly sensitive to the model on which they are based. A comparison between theory and experiment with respect to the temperature dependence of adsorption is somewhat more discriminating than the isotherms themselves. 

As far as toxicology is concerned, one must distinguish between soot, which is formed by the uncontrolled combustion of coal and oil, and carbon black, which is industrially produced under precisely defined conditions. Commercial carbon blacks are characterized by an atomic ratio H C of <0.1, low ash content, and high adsorption capacity. The soluble organic fraction (extractable materials) is less than 0.5 wt%. 

To model the process, a mass balance is made for the adsorbed species, and the partial pressures of the reactants are considered as constant. The surface coverage of each adsorbed species is defined as the fraction of the total number of available adsorption sites occupied by that species and denoted by 0A or 0B. The differential equations for this mechanism are ... 

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