Free energy of adsorption standard

Standard Free Energies of Adsorption of B and BH. The standard free energy of adsorption of C12BMG was calculated from the surface tension data in Figures 1 and 2 by use of the equation ... 

AG°s is the standard free energy of adsorption of the solute to the stationary phase surface ([) is the column phase ratio... 

The data in Table 1 shows that the standard free energy of adsorption increases, on average, by 2.5 kj/mol for each methylene group added to the hydrophobic tail. However, the intermolecular interaction parameter p in... 

Fig. P6.2. Temperature dependence of the standard free energy of adsorption for (a) CF3SO3 and (b) H3P04 (E = 0.80 V). (Reprinted from P. Zelenay, B. R. Scharifker, J. O M. Bockris, and D. Gervasio, J. Electrochem. Soc. 133 2262, copyright 1986, Fig. 4, with permission of Elsevier Science.)...

Figure P6.4 shows the logarithmic dependence of the adsorption of chloride ions, log(T - r/r, on time, /(min). The adsorbing metal is aluminum, the concentration of chloride ions in solution is 1(T3 mol dm-3 at pH 12, and the potential in the hydrogen scale is -0.9 V. On the assumption that the adsorption is diffusion controlled, determine the standard free energy of adsorption of chloride ions on the surface concerned. 

For anionic monolayers, the reversal of the tt-A isotherms can be explained in terms of a competition between the anionic head groups and the alkali metal cations for molecules of water. If a modified Stern-type model of the plane interface is assumed, this interface will be composed of distinct adsorption sites, with counterions (cations) of finite size that can adsorb on these sites if the standard free energies of adsorption are favorable. If the anionic head group is more polarizable than water, as with carboxylic acids or phosphates, the hydration shell of the cation is incompletely filled, and the order of cation sizes near the interface is K+ > Na+ > Li+. When the polarizability of the anionic group is less than that of water, as with the sulfates, the lithium cation becomes the most hydrated one, and the order of cation sizes becomes Li+ > Na+ > K+. 

In these cases, the standard free energy of adsorption can be obtained from the equilibrium condition and is a simple exponential function of the potential which does not depend significantly on the charge distribution at the interface for an uncharged adsorbate. The chemisorption thus corresponds to a vertical shift in the free energy curves as depicted in Fig. 12 and affects the energy of activation [76]. 

From the slope and intercept of these plots the saturation coverage and adsorption coefficient were obtained by application of the previously given equation. The results are listed in Table I, which also includes the area per dye molecule at saturation coverage and the standard free energy of adsorption, AG°. Although the latter parameter was calculated as before (23), its thermodynamic validity is questionable since reversibility of adsorption of these dyes was not demonstrated. The molecular... 

The standard free energy of adsorption from either bulk phase was calculated from interfacial tension isotherms ... 

Recent studies showed that amphiphilic properties have to be taken into account for most water-soluble monomer units when their behavior in water solutions is considered. The amphiphilic properties of monomer units lead to an anisotropic shape of the polymer structures formed under appropriate conditions, which is confirmed both by computer simulation and experimental investigations. The concept of amphiphilicity applied to the monomer units leads to a new classification based on the interfacial and partitioning properties of the monomers. The classification in question opens a broad prospective for predicting properties of polymer systems with developed interfaces (i.e., micelles, polymer globules, fine dispersions of polymer aggregates). The relation between the standard free energy of adsorption and partition makes it possible to estimate semiquantitatively the distribution between the bulk and the interface of monomers and monomer units in complex polymer systems. 

Fig. 4.5 Standard free energy of adsorption as a function of temperature for (a) IC and (b) PEO in aqueous solution. (From ref. [28])...

Fig. 12.45. The standard free energy of adsorption of families of organics as a function of the standard free energy of solution. Note the difference in sign. Adsorption occurs more readily as the tendency to dissolve declines. (Reprinted with permission from E. Blomgren, J. O M Bockris, and K. Jesch, J. Phys. Chem. 65 2006, copyright 1961 American Chemical Society.)...

The formation of dimers in solution at higher concentrations indicates an interaction between the dye molecules and so the b term in the Frumkin isotherm is not a surprise. The adsorption behaviour suggests that the dye is highly surface-active and formation of a monolayer is almost complete by the transition at ca. 6 pM. The standard free energy of adsorption derived from the isotherm is consistent with a monolayer coverage forming even at the micromolar aqueous concentrations. Once the first layer is substantially complete, subsequent adsorption takes place on this layer to form a second-ordered layer. 

The assumption that the standard free energy of adsorption is independent of coverage may be viewed as the "zeroth-order approximation. The first-order approximation will then be a linear dependence of AG° on 0 ... 

In Fig. 31 we show positive as well as negative values of the parameter r. What is the physical meaning of r < 0, namely of an increase in the absolute value of the standard free energy of adsorption with coverage We have seen that a positive value of r can be due either to a surface inhomogeneity or to lateral repulsion interactions. A negative value of the same parameter hence must correspond to lateral attraction interactions, which lead to an increase of the equilibrium... 

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