Neutral Langmuir isotherm

The second example is the extraction of Ni(II) with 2-hydroxy oxime. 2-Hydroxy oxime including 5-nonylsalicylaldoxime (P50) [15], 2-hydroxy-5-nonylacetophenone oxime (SME529) [16], and 2-hydroxy-5-nonylbenzophenone oxime (LIX65N) [17], are widely used as commercial extractants of Ni(II), Cu(II), and Co(II) in hydrometallurgy. These extractants are adsorbed at the interface even in their neutral forms following the Langmuir isotherm,... 

Sorption. Capture of neutral organics by non-living particulates depends on the organic carbon content of the solids (9). Equilibrium sorption of such "hydrophobic" compounds can be described by a carbon-normalized partition coefficient on both a whole-sediment basis and by particle size classes. The success of the whole-sediment approach derives from the fact that most natural sediment organic matter falls in the "silt" or "fine" particle size fractions. So long as dissolved concentrations do not exceed 0.01 mM, linear isotherms (partition coefficients) can be used. At higher concentrations, the sorptive capacity of the solid can be exceeded, and a nonlinear Freundlich or Langmuir isotherm must be invoked. 

Figure 5 shows the adsorbent loading, Q, as a function of C°, based on data at various pHs. The result suggests that the neutral form of berberine was adsorbed on XAD-7. This result was consistent with the result that adsorption onto XAD-7 was due to hydrophobic interaction. In Fig. 5, the adsorption isotherm for berberine was of the Langmuir isotherm type. This result suggested that berberine might be adsorbed onto XAD-7 form a monolayer. 

Lipatov798 recognized that the sorption of Methylene Blue on starch is a heterogenous neutralization reaction of neutralization in which starch acts as an acid. Adsorption isotherms of Methylene Blue on starch indicate that it is an equilibrium process and that swelling as well as other internal structural factors are responsible for the sigmoidal shape of the isotherm.799-800 It is also known that the Langmuir isotherm is affected by equilibrium between the monomer and dimer forms of Methylene Blue, both of which are capable of adsorption on starch (Table XLV).801... 

Fig. IIJ Langmuir isotherm for the electrosorption of a large neutral species, each adsorbate molecule replacing n water molecules from the surface.

Ammons et al. studied the adsorption of methyl mercuric chloride from aqueous solutions on Filtrasorb-200 activated carbon at room temperature and found that the adsorption isotherms were nonlinear and did not fit either the Freundlich or the Langmuir isotherm equation. The adsorption was, however, reversible. Carrot et al. carried out adsorptive removal of mercury(ll) ions on five different commercial activated carbons associated with varying amounts of acidic and basic surface complexes. These workers observed that significant amounts of HgC and HgCl were adsorbed, but there was little adsorption of neutral HgCl2 or Hg + ions, hi the case of the basic carbons, the adsorption of the anions decreased with increase in the pH of the solution, but the uptake of cations was very small at pH = 0.2. They are of... 

Here e is the bulk permittivity of water, F is Faraday s constant, I is the ionic strength, and z the ionic charge. For adsorption on a homogeneous surface the neutral and ionized forms of the electrolyte are competing for the same number of sites, and Langmuir isotherms giving the fractional coverage 6 of each species may be written ... 

Figure 24. Neutralization isotherms (adsorption isotherm of OH") for acidic surface groups on a carbon black The lower plot represents the linearized isotherms according to a modified Langmuir adsorption model.

When two coexisting phases are subjected to the condition that one or several of the ionic components cannot pass from one phase to the other, a particular type of equilibrium is set up, called a Dorman equilibrium. This type of ionic equilibrium is unique for ionic absorbents containing a fixed ion, and the isotherm describing such equilibria differs from the established Langmuir Freundlich and Bru-nauer, Emmett, and Teller types which are found for neutral species. 

The adsorption of either ions or neutral molecules on the electrode surface depends on qn, i.e., on the apphed electric potential. Correspondingly, the electric field at the electrochemical interface is an additional free-energy contribution that either favors or restricts the adsorption of species on the electrode from the ionic conducting phase. A variety of adsorption isotherms has been proposed to account for the behavior of different electrochemical systems. Among them are the Langmuir, Frumkin, and Temkin isotherms [2]. Frumkin and Temkin isotherms, at variance with the Langmuir one, include effects such as adsorbate—adsorbate or adsorbate—surface interactions. 

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