Adsorption organic molecules

Similarly, the crystal structure of the electrode influences the adsorption process of organic molecules. Adsorption on the most compact surfaces is generally stronger than in the most open surfaces. Thus, organic molecules tend to adsorb in the following order (111) > (100) > (110), as shown in Figure 6.115 for the adsorption of various organic substances on different crystal faces of various metals (Trasatti, 1995). 

We emphasize two natural limitations of the finite cluster model. It does not allow to make a statement about the dependence of essential parameters such as adsorption and transition energies on the level of surface coverage, and it does not account adequately for charge delocalization or surface relaxation phenomena. Further, it excludes by definition any information about the modification of the surface band structure as a consequence of the organic molecule adsorption. The following case study of 1-propanol on Si(001) - (2 x 1) is intended to clarify how these elements can be consistently incorporated into the description of the Si surface interaction with organic species. 

Equation 10.20 describes the S-shaped isotherm commonly observed in studies of organic molecule adsorption on clays from aqueous solution. 

Organic molecules adsorption (organic fouling, e.g. proteins, humic substances)... 

As will be demonstrated in this chapter, there has been a strong evolution of fundamental studies recently, giving rise to new concepts that will be explored. In tbe present review, we summarize fundamental approaches used to characterize organic molecule adsorption on model metal (and oxidized) surfaces, in relation to their corrosion inhibition properties, by means of atomistic simulations. 

The field X is taken as that due to a surface charge density i e., X = 47T M/e, where e is the effective dielectric constant of the interphase. This theory provides a good basis for quantitative interpretation of organic molecule adsorption but when the organic molecule is n times as large as the adsorbed solvent, the form of the isotherm will be... 

Also, in further developments of this kind of treatment, specific structureforming and structure-breaking effects of the organic adsorbate must be considered in relation to the orientation of solvent molecules, e.g., as indi-cated by entropies and heats of adsorption of pyridine at Hg electrodes. Analysis of various types of isotherms which represent organic molecule adsorption has been made by Kovac and Bockris and by Wroblowa and Mueller in relation to the theory presented above. 

Charge-Transfer Compounds. Similat to iodine and chlorine, bromine can form charge-transfer complexes with organic molecules that can serve as Lewis bases. The frequency of the iatense uv charge-transfer adsorption band is dependent on the ionization potential of the donor solvent molecule. Electronic charge can be transferred from a TT-electron system as ia the case of aromatic compounds or from lone-pairs of electrons as ia ethers and amines. 

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... 

Many molecules undergo partial oxidation on adsorption and many alkanes and alkenes are believed to yield an adsorbed CHO group on adsorption (Petrii, 1968). These processes usually lead to the complete oxidation of the organic molecule to carbon dioxide and few workers have attempted to halt the reaction at an intermediate stage. Hence, although there are undoubtedly possibilities for using dissociative chemisorption for synthetic reactions, this chapter will not consider these processes further. 

Reactions on the surface are interesting. The adsorptions of unsaturated organic molecules on the surface provide a means for fabricating well-ordered monolayer films. Thin film organic layers can be used for diverse applications such as chemical and biological sensors, computer displays, and molecular electronics. 

A fourth separation technique employs charcoal. Charcoal has adsorption characteristics such that most organic molecules will adhere to its surface. However, charcoal is also very porous, thereby allowing smaller molecules to enter into its pores and become trapped in them. The charcoal is first coated with dextran or hemoglobin which covers its outer surface. 

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