Organic solutes adsorption, from aqueous solution

Fig. 8.34 Parathion adsorption from aqueous solutions by three soils, before and after oxidation, as weU as on clay and organic matter. Reprinted with permission from Saltzman S, Kliger L, Yaron B (1972) Adsorption-desorption of parathion as affected by soil organic matter. J Agric Food Chem 20 1224-1227. Copyright 1972 American Chemical Society...

Figure 11.1. Schematic views of various ways in which an organic chemical, i, may sorb to natural inorganic solids (a) adsorption from air to surfaces with limited water presence, (b) partitioning from aqueous solutions to the layer of vicinal water adjacent to surfaces that serves as an absorbent liquid, (c) adsorption from aqueous solution to specific surface sites due to electron donor-acceptor interactions, (d) adsorption of charged molecules from aqueous solution to complementarily charged surfaces due to electrostatic attractions, and (e) chemisorption due to surface bonding or inner sphere complex formation.

In addition, the polymers of intrinsic microporosity (PIMs), such as phthalocyanine networks and the Co phthalocyanine network-PIM (CoPc20), display high specific surface area, as confirmed by the N2 adsorption isotherm at 77 K, and by the adsorption of small organic probe molecules from aqueous solutions at 298 K [236], This material is basically microporous with an increased concentration of effective nanopores. 

In simple adsorption from aqueous solution, Hg has features in contrast and in common with the base metals. The hydroxy-cation is the active species in the model for heavy-metal adsorption and this also appears to be true for Hg. However, in contrast with Cu, Pb and Zn, the adsorption is less efficient and is strongly inhibited by the formation of halide complexes, as has been shown by Forbes et al. (1974) (Fig. 12-1). These authors also demonstrate that the adsorption of Hg to goethite is effective at pH as low as 4, allowing it to be trapped subsequent to sulphide oxidation. Whilst many minerals in weathered rocks and soils may each adsorb Hg, the relative efficiency of the hydrous iron oxides (Andersson, 1979) implies that these phases will be the dominant host in most exploration samples. However, the soil organic matter is also of importance and, although the association with Hg has been described as adsorption, it seems more... 

The inorganic materials involve the silica, montmorillonite, allapulgite, FCjO, ZnCl, CuCl, etc. The as-prepared composites can absorb versatile organic and inorganic pollutants from aqueous solutions. Different silica crystalline forms were utilized to fabricate various PANI/silica composites for water purification. PANI were coated on silica gel to modify its surface morphology and to improve its adsorption capacity for phenol [35] and acid green 25 [36] adsorption from aqueous solutions. 

Ammons, Dougharty, and Smith have studied the adsorption of methyl-mercuric chloride from aqueous solution by activated carbon by both batch and flow techniques. The data were analysed to investigate the factors that control the breakthrough curves. Axial dispersion was found to contribute no more than 15% to the second moment of the breakthrough curve, while liquid-to-particle mass transfer contributed about 60%. On a similar topic Benediktov, Vlasov, and Yurkevich in a paper of which only the title is abstracted, discuss the determination of the degree of exhaustion of active carbon with respect to organic substances during adsorption from aqueous solutions. 

The literature relevant to adsorption from aqueous solutions is extensive and confusing. A dominant reason for this is that many of the smdies are not comprehensive enough, meaning that an individual study must look, without exception, at all of the variables which influence extents of such adsorptions. The same variables apply, more or less equally, to adsorptions of both inorganic and organic solutes. 

Zhang et al. [31] used a Calvet calorimeter to measure as a function of S, the apparent adsorption, for the adsorption from aqueous solution of several different organic compounds on Na-montmorillonite. The apparent adsorption is the difference between the amount of organic compound actually present in the system per unit mass of montmorillonite and that which would be present if the concentration of the compound in the equilibrium solution persisted up to the montmorillonite/water interface. Their results are reproduced in Fig. 15. Observe from this figure that Q, was negative for some of the... 

Hydrophilic and Hydrophobic Surfaces. Water is a small, highly polar molecular and it is therefore strongly adsorbed on a polar surface as a result of the large contribution from the electrostatic forces. Polar adsorbents such as most zeoHtes, siUca gel, or activated alumina therefore adsorb water more strongly than they adsorb organic species, and, as a result, such adsorbents are commonly called hydrophilic. In contrast, on a nonpolar surface where there is no electrostatic interaction water is held only very weakly and is easily displaced by organics. Such adsorbents, which are the only practical choice for adsorption of organics from aqueous solutions, are termed hydrophobic. 

Brasquet, C., Subrenat, E. and Le Cloirec, P., Selective adsorption on fibrous activated carbon of organics from aqueous solution Correlation between adsorption and moleeular strueture. Water Sci. Technol., 1997, 35(7), 251 259. 

Adsorption, which utilizes the ability of a solid adsorbent to adsorb specific components from a gaseous or a liquid solution onto its surface. Examples of adsorption include the use of granular activated carbon for the removal of ben-zene/toluene/xylene mixtures from underground water, the separation of ketones from aqueous wastes of an oil refinery, aad the recovery of organic solvents from the exhaust gases of polymer manufacturing facilities. Other examples include the use of activated alumina to adsorb fluorides and arsenic from metal-finishing emissions. 

Adsorption from liquids is less well understood than adsorption from gases. In principle the equations derived for gases ought to be applicable to liquid systems, except when capillary condensation is occurring. In practice, some offer an empirical fit of the equilibrium data. One of the most popular adsorption isotherm equations used for liquids was proposed by Freundlich 21-1 in 1926. Arising from a study of the adsorption of organic compounds from aqueous solutions on to charcoal, it was shown that the data could be correlated by an equation of the form ... 

In any study of electrosorption of neutral molecules on metallic electrodes, the ions of supporting electrolytes should not be specifically adsorbed. Nevertheless, the interaction of the electrolyte ions with the electrode surface may depend on the interaction of the ions with the solvent. Usually, the stronger the ion-solvent interaction, the weaker the adsorption of the ion. Since the ions are more weakly solvated in nonaqueous solvents than in water, the ions that are not adsorbed from aqueous solutions may still be adsorbed from organic solvents. However, even in the absence of... 

FIGURE 5.24 (See color insert following page 280.) Schematic comparison of the adsorption mechanisms of a solute from aqueous solutions of (a) methanol and (b) acetonitrile onto a RPLC material. Three different phases (bulk mobile phase, the adsorbed mono- or multilayer of organic modifier molecules, and the C is phase) are involved in the chromatographic system. The solute is represented by small ovals. (Reproduced from Gritti, F. and Guiochon, G, Anal. Chem., 77, 4257, 2005. With permission.)... 

LDHs are also promising materials as sorbents for anionic organic contaminants via both ion-exchange and reconstruction reactions. There have been a large number of reports of the use of LDHs for removal of species such as aromatic carboxylic acids, phenols, pesticides, and humic or fulvic acids. Recently, Cardoso et al. [152] found that the sorption process of terephthalate anions from aqueous solutions by calcined Mg/Al - CO3 LDHs takes place by reconstruction of the LDHs and involves the intercalation and adsorption of terephthalate anions. Calcined Mg/Al - CO3 LDHs were found to be capable of removing 40 to 85 % of the benzoate from solutions in the concentration... 

Boyd GE, Adamson AW, Myers LS (1947) The exchange adsorption of ions from aqueous solutions by organic zeolites II. Kinetics. J Am Chem Soc 69 2836-2848 Brindley GW, MacEwan DMC (1953) Structural aspects of the mineralogy of clays and related silicates. In Green AT, Stewart GH (eds) Ceramics—A Symposium. The British Ceramic Society, Stoke-on-Trent UK, pp 15-59... 

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