Ternary adsorption

Rietra et al. (2001) measured the simultaneous adsorption of phosphate and calcium on goethite over the pH range 4-11 and modelled the data with the CD-MU-SIC model. They concluded that the observed adsorption took place in response to electrostatic effects and that ternary adsorption was not involved. 

The presence of anions in solution may enhance cation adsorption by formation of mixed metal/ligand surface complexes (Schindler, 1990). This effect is termed ternary adsorption. Two forms of ternary adsorption have been identified  

The case where a polydentate ligand bridges the adsorbed metal ion and the surface metal ion, i. e. 

To date, only the second form of ternary adsorption has been observed for iron oxides. Davis and Leckie (1978 a) found that thiosulphate adsorbed on ferrihydrite in acid media with adsorption decreasing to zero as the pH rose to ca. 7, whereas the adsorption edge of silver lay between pH 7 and 8. In the presence of thiosulphate, adsorption of silver was enhanced in the pH range 4-6.5 (Fig. 10.10), i. e. 

The effect increased with increasing concentration of thiosulphate. Above pH 7, thiosulphate suppressed adsorption of Ag by holding the cation as a complex in solution. Adsorption of Ag on ferrihydrite was also enhanced by glutamic acid and that of Cu was promoted by both glutamic acid and by 2.3-pyrazidinedicarboxylic acid. 

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In systems containing two or more adsorbates, either competitive or synergistic effects may operate. The commonest synergistic effect is that of ternary adsorption (11.5.4). Competitive behaviour may involve competition for the same surface sites, indirect effects due to the change in the electrostatic properties of the oxide/water interface and in some cases, formation of non sorbing, metal-ligand complexes in solution. 

Ternary adsorption of humic molecules and Ca ions modified the surface charge and the colloidal behaviour of goethite (Tipping and Cooke, 1982). Fe oxides in natural environments often form in the presence of or through the activity of, micro-organisms (see Chap. 17). The adsorption properties of the oxides may, therefore, be modified by adsorbed organic molecules and ternary Fe-OCO-M complexes (CO-org. 

Consideration is now given to the experimental variables relating to the adsorption of surfactant mixtures. The adsorption isotherm of component 1 in a ternary system is again defined by Equation (1). However, the isotherm is now three-dimensional and for a consistent two-dimensional presentation, a constant ratio of X2/X2 seems to be a logical choice (components 1 and 2 are surfactants, component 3 is water or brine). Figure 4 represents a ternary adsorption isotherm surface. 

Hu, X., and Do, D.D., Contribution of concentration-dependent surface diffusion in ternary adsorption kinetics of ethane, propane and n-butane in activated carbon. Adsorption, 2(3), 217-226 (1996). 

For practical purposes so-called Gibbs ternary diagrams are very useful to present ternary adsorption equilibria An example for this is given in the next Figure 3.27. It again refers to (CH4, CO2, N2) gas mixtures being adsorbed at four different concentrations on AC NORIT Rl at T = 298 K and a total gas pressure p = 1 MPa, [3.27]. 

In the reaction of an enzyme with two substrates, the binding of the substrates can occur sequentially in a specific order. Thus, the binding mechanism can be divided into catalysis which proceeds through a ternary adsorption complex (enzyme -h two substrates) or through a binary complex (enzyme -h one substrate), i. e. when the enzyme binds only one of the two available substrates at a time. 

As noted above, adsorption isotherms are largely derived empirically and give no information on the types of adsorption that may be involved. Scrivner and colleagues39 have developed an adsorption model for montmorillonite clay that can predict the exchange of binary and ternary ions in solution (two and three ions in the chemical system). This model would be more relevant for modeling the behavior of heavy metals that actively participate in ion-exchange reactions than for organics, in which physical adsorption is more important. 

The reference Pt-Ba/y-Al203 (1/20/100 w/w) catalyst shows surface area values in the range 140-160 m2/g, a pore volume of 0.7-0.8cc/g and an average pore radius close to 100 A (measured by N2 adsorption-desorption at 77 K by using a Micromeritics TriStar 3000 instrument). Slight differences in the characterization data are associated to various batches of the ternary catalyst [24,25],... 

The role of the Pt-Ba interaction in the mechanism of adsorption of NO species was also studied by a kinetic model reported in the literature [16]. The model, which consists of 10 elementary reversible steps, is based on the oxidation of NO to N02 over Pt and on the storage of N02 over Ba, and it was used to simulate the data collected over both the physical mixture and the ternary Pt-Ba/y-Al203 1/20/100 w/w sample. A spillover reaction between Pt and Ba oxide sites has also been included in the model to account for the observed lower thermal stability of Ba-nitrates in the presence of Pt [16]. Essentially, the model assumes that the adsorption of NO proceeds through the nitrate route and does not consider the nitrite route. 

The TRM runs of N02 adsorption in the presence of C02 on the ternary Pt—Ba/Al203 catalyst at 350°C (Figure 6.8a) showed that, like in the absence of C02, (see Figure 6.3), the NO adsorption occurred via N02 disproportionation with evolution of NO. Also in the presence of carbon dioxide, the NO storage is accompanied by N02 decomposition on Pt sites, with evolution of NO and 02. 

Recent reports describe the use of various porous carbon materials for protein adsorption. For example, Hyeon and coworkers summarized the recent development of porous carbon materials in their review [163], where the successful use of mesoporous carbons as adsorbents for bulky pollutants, as electrodes for supercapacitors and fuel cells, and as hosts for protein immobilization are described. Gogotsi and coworkers synthesized novel mesoporous carbon materials using ternary MAX-phase carbides that can be optimized for efficient adsorption of large inflammatory proteins [164]. The synthesized carbons possess tunable pore size with a large volume of slit-shaped mesopores. They demonstrated that not only micropores (0.4—2 nm) but also mesopores (2-50 nm) can be tuned in a controlled way by extraction of metals from carbides, providing a mechanism for the optimization of adsorption systems for selective adsorption of a large variety of biomolecules. Furthermore, Vinu and coworkers have successfully developed the synthesis of... 

Schindler, P. W. (1990), "Co-Adsorption of Metal Ions and Organic Ligands Formation of Ternary Surface Complexes", in M. F. Jr.. Hochelia and A. F. White, Eds., Mineral-Water Interface Geochemistry, Mineralogical Soc. of America, Washington, DC, 281-307. 

The retention of Cu by allophane is enhanced by phosphate regardless of the sequence of Cu and phosphate adsorption, although Cu has been found to have no effect on the simultaneous and subsequent adsorption of phosphate on surface bound Cu (32) ESR results suggest that the Cu binds to surface A10H groups of the allophane irrespective of the presence of phosphate and it was proposed that the enhanced Cu retention was the result of the formation of a ternary complex by the binding of phosphate to the axial position of the surface-bound Cu ion. 

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