Adsorption of organic molecules

A theoretical description of hydrogen bonding effects can be made from model of charge-controlled adsorption. It was found that the energy of adsorption of organic molecules ai e determined by the ratios between the effective chai ges of their atoms and atoms in polai solvent molecules ... 

In connection with the adsorption of organic molecules at the surface of an electrode it is possible to distinguish two types (a) adsorption of undissociated molecules and (b) adsorption of intermediates formed by dissociation of the original molecule. The variation of coverage of the surface of a... 

Clay minerals or phyllosilicates are lamellar natural and synthetic materials with high surface area, cation exchange and swelling properties, exfoliation ability, variable surface charge density and hydrophobic/hydrophilic character [85], They are good host structures for intercalation or adsorption of organic molecules and macromolecules, particularly proteins. On the basis of the natural adsorption of proteins by clay minerals and various clay complexes that occurs in soils, many authors have investigated the use of clay and clay-derived materials as matrices for the immobilization of enzymes, either for environmental chemistry purpose or in the chemical and material industries. 

The adsorption of organic molecules offers a rich phenomenology. A large number of studies have been performed on mercury electrodes, where the surface tension can be measured directly, and the surface charge and the capacity obtained by differentiation. We will not attempt to survey the literature, but consider a simple example the adsorption of aliphatic compounds. 

Adsorption of organic molecules under vacuum conditions... 

Studying the adsorption of organic molecules with the semiconductor surfaces under vacuum conditions allows the reactivity of the reconstructed surfaces to be investigated. In the case of (100)-2 x 1 reconstructed surfaces of silicon and germanium,... 

Reference electrode, 1104, 1108, 1113 potential, 819, 874 Refractive index, determination with ellipsometry, 1148. 1151 Reflection coefficient, 1151 Residence time, definition, 1310 Reversal techniques, determination of intermediate radicals, 1416 Reversible adsorption of organic molecules, 969, 970... 

The specific methodology involved in these simulations is beyond the scope of this chapter. So, instead of extending our knowledge of adsorption of ions on electrodes, in the next section we will study the characteristics of the adsorption process of other types of species, the adsorption of organic molecules. 

Fig. 6.108. Current vs. potential curve for the adsorption of organic molecules on electrodes. The current due to adsorption of organic molecules is a currentless process. When oxidation, reduction, or other electron-transfer reactions take place, high currents may be detected.

Correspondingly, the forces involved in the adsorption of organic molecules can be classified into three categories organic molecule-electrode forces, water-electrode forces, and lateral interactions. These forces are the same as those we studied in the adsorption of ions on electrodes, and their nature was described in Section 6.8.2. 

Thus, Eq. (6.270) is an isoconc (see Section 6.8.6), which describes the adsorption of organic molecules on electrodes as a substitution process of solvent molecules and takes into account the surface heterogeneity and lateral interactions among the adsorbed species. This isoconc is able to successfully describe and reproduce the parabolic shape—with its maximum in the vicinity of the pzc—of the adsorption process of organic molecules. 

Other Factors Influencing the Adsorption of Organic Molecules on Electrodes... 

Goss, K.-U., Considerations about the adsorption of organic molecules from the gas phase to surfaces Implications for inverse gas chromatography and the prediction of adsorption coefficients , J. Colloid Interface Sci., 190, 241-249 (1997a). 

Acid-base surface sites, adsorption of organic molecules, 23... 

In contrast to the minimal activity in infrared reflection studies the technique of inelastic electron tunneling spectroscopy (IETS) recently has contributed a large amount of information on monolayer adsorption of organic molecules on smooth metal oxide surfaces,Q),aluminum oxide layers on evaporated aluminum. These results indicate that a variety of organic molecules with acidic hydrogens, such as carboxylic acids and phenols chemisorb on aluminum Oxide overlayers by proton dissociation - 1 — and that monolayer coverage can be attained quite repro-ducibly by solution doping techniques. - The IETS technique is sensitive to both infrared and Raman modes. — However, almost no examples exist in which Raman il and or infrared spectra have been taken for an adsorbate/substrate system for which IETS spectra have been observed. 

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