Organic solutes, adsorption

The succeeding material is broadly organized according to the types of experimental quantities measured because much of the literature is so grouped. In the next chapter spread monolayers are discussed, and in later chapters the topics of adsorption from solution and of gas adsorption are considered. Irrespective of the experimental compartmentation, the conclusions as to the nature of mobile adsorbed films, that is, their structure and equations of state, will tend to be of a general validity. Thus, only a limited discussion of Gibbs monolayers has been given here, and none of such related aspects as the contact potentials of solutions or of adsorption at liquid-liquid interfaces, as it is more efficient to treat these topics later. 

The most frequently used methods of analyte isolation and concentration for organic compounds involve distillation, extraction auid adsorption techniques. Some typical applications of these techniques and their attendant -advantages and disadvantages for the analysis of trace organic solutes in water are summarized in Table 8.1 [4,26]. These methods will be elaborated on below and in subsequent sections of this chapter. 

Cosovic, B. (1990), "Adsorption Kinetics of the Complex Mixture of Organic Solutes at Model and Natural Phase Boundaries , in W. Stumm, Ed., Aquatic Chemical Kinetics, John Wiley and Sons, New York, 291-310. 

The mechanisms of adsorption of organic solutes—including hydro-phobic, polar, and ionic species—onto surfaces have been summarized previously (2 5). Assuming that the various adsorptive mechanisms act independently, the free energy of adsorption (AGa[Pg.192]

The arguments presented above lead to the conclusion that the adsorption of nonionic compounds such as halogenated hydrocarbons results primarily from "hydrophobic bonding" or, perhaps more appropriately, the hydrophobic interaction (7). The thermodynamic driving force for hydrophobic interactions is the increase in entropy resulting from the removal, or decrease, in the amount of hydration water surrounding an organic solute in water. Studies have shown that the adsorption of aliphatic amines onto clays (8)... 

Electrode surfaces can be modified by redox polyelectrolytes via a sol-gel process, yielding random redox hydrogels or by layer-by-layer self-assembly of different redox and nonredox polyelectrolytes by alternate electrostatic adsorption from solutions containing the polyelectrolytes to produce highly organized redox-active ultrathin multilayers. 

In Chapter 4, we saw how conservative chemicals are used to trace the pathway and rates of water motion in the ocean. True conservative behavior is exhibited by a relatively small number of chemicals, such as the major ions and, hence, salinity. In contrast, most of the minor and trace elements display nonconservative behavior because they readily undergo chemical reactions under the environmental conditions found in seawater. The rates of these reactions are enhanced by the involvement of marine organisms, particularly microorganisms, as their enzymes serve as catalysts. Rates are also enhanced at particle interfaces for several reasons. First, microbes tend to have higher growth rates on particle surfaces. Second, the solution in direct contact with the particles tends to be highly enriched in reactants, thereby increasing reaction probabilities. Third, adsorption of solutes onto particle surfaces can create fevorable spatial orientations between reactants that also increases reaction probabilities. 

Activated charcoal or carbon is widely used for vapour adsorption and in the removal of organic solutes from water. These materials are used in industrial processes to purify drinking water and swimming pool water, to de-colorize sugar solutions as well as other foods, and to... 

The material in this chapter is organized broadly in two segments. The topics on monolayers (e.g., basic definitions, experimental techniques for measurement of surface tension and sur-face-pressure-versus-area isotherms, phase equilibria and morphology of the monolayers, formulation of equation of state, interfacial viscosity, and some standard applications of mono-layers) are presented first in Sections 7.2-7.6. This is followed by the theories and experimental aspects of adsorption (adsorption from solution and Gibbs equation for the relation between... 

These methods have been applied to the study of adsorption of a variety of organic solutes by inorganic and organic solid substrates. 

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