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Maximum extents of adsorption

Surface Activity Parameters The surface activity parameters of sinfac-tants are mainly obtained via surface tension measurement [36, 37, 40, 42, 44, 46]. From the surface tension, isotherms of the saturation surface excess, can be calculated using the Gibbs adsorption equation, which is used as a measure of maximum extent of adsorption of surfactant at the air/solution or solution/solution interface. [Pg.133]

The surface excess concentration under conditions of surface saturation, T, may conveniently be used as a measure of the maximum extent of adsorption of a surfactant. Several factors determine the maximum amount of surfactant which can be adsorbed at an interface. [Pg.18]

When added phosphonate concentrations are increased at fixed surface loading and pH, Ae extent of adsorption eventually levels out. Maximum extents of adsorption provide an estimate of the "footprint" of each molecule on the surface. Footprint size may reflect the numbers of surface-bound Fe atoms engaged in bond formation with the adsorbed molecule, or may indicate crowding by neighboring molecules. Electrostatic repulsion between like-charged adsorbate molecules on the surface may also be important. [Pg.80]

Figure 10, Maximum extents of adsorption for eight phosphonate-containing compounds onto 0.42 g/L FeOOH(goethite). Reaction conditions 1 mM MOPS buffer (pH 7.2), lO.OmMNaNOs (data from ref (41). Figure 10, Maximum extents of adsorption for eight phosphonate-containing compounds onto 0.42 g/L FeOOH(goethite). Reaction conditions 1 mM MOPS buffer (pH 7.2), lO.OmMNaNOs (data from ref (41).
For the Langmuir adsorption isotherm it is assumed that this reaction (Eq. 1) has a fixed free energy of adsorption equal to AG°, which is not dependent on the extent of adsorption and not affected by interaction among sites. In addition, each site is assumed to be capable of binding at most one molecule of adsorbate. If Q is the maximum number of moles of a pollutant adsorbed per mass adsorbent when the surface sites are saturated with an adsorbate (i.e., a full monolayer), and q is the number of moles of adsorbate per mass adsorbent at equilibrium, then according to the law of mass action Eq. (2) follows ... [Pg.173]

Phosphonates adsorb on goethite up to a pH of 12, although like carboxylic acids, maximum adsorption is at low pH. The extent of adsorption rises as the number of phosphonate groups increases from one to five. Nitrilo trismethylene phosphonic acid (NTMP) adsorbs on goethite within minutes at pH 7. Complete desorption is effected at pH 12 after a number of hours. Equimolar amounts of Ca promote uptake of NTMP on goethite (Nowack and Stone, 1999). [Pg.274]

The pH of a solution influences the extent of adsorption. The majority of pharmaceutically active drugs are weak acids or weak bases. The degree of ionization and solubility of the adsorbate drug molecule are dependent on pH. As described above, more ionized (i.e., polar) and soluble adsorbates adsorb much less than their unionized forms (i.e., lypophilic) do. For amphoteric adsorbates, a maximum adsorption capacity occurs at the isoelectric point (IEP), where the net charge of the adsorbate becomes zero, and at the lowest solubility. In general, pH and solubility... [Pg.216]

In the range of potentials of an adsorption-desorption capacity peak, the extent of adsorption changes so rapidly with potential that the superposition of an alternating signal (for measurements) of different amplitude or frequency produces different values of the differential capacity.t Therefore, the potential of the adsorption-desorption capacity peak and potential (or density of charge) at the maximum of adsorption are often used as parameters characterizing adsorption because they are less subject to error. [Pg.86]

The relationship between extent of adsorption and gas pressure shown in Figure 4.5 is by no means the only relationship known. Strictly, it applies only when maximum adsorption results in a monolayer of adsorbate on the surface. Two of the other observed types of adsorption behavior are shown in Figure 4.7. [Pg.142]

For each group, there are subgroups mainly defined by the extent of adsorption reached. It should be noted that often, due to the nature of the systans, the experimentally accessible concentration range is limited, thus the maximum amount sorbed may be far from samration coverage. [Pg.70]

Concentration changes of acetic acid were measured by titration with a standard sodium hydroxide solution. Extents of adsorption of acetic acid on 850 °C PVDC carbons (0,41 and 70 wt% bum-off) are plotted against acetic acid concentration in Figure 8.3. Extents of adsorption of acetic acid by the carbons reached a maximum in about 4M acetic acid (mole fraction = 0.09). The maximum amounts of acetic acid plotted in these isotherms (Figure 8.3) correspond more to capillary condensation than pore filling mechanisms (Table 8.1) with the possibility of capillary condensation of hydrated acetic acid molecules. Thus, no unequivocal conclusions are possible. The conclusions of this study, relevant to understanding adsorptions from solution are as follows ... [Pg.386]

Unlike adsorptions of metal ions (M" ) a phenol, in aqueous solution, can exist as a non-dissociated and as an anionic phenolate, dependent on the pH, the more acidic the solution, the higher the concentration of the phenol molecule. Thus, the mechanisms of adsorption of a phenol change drastically with pH. In the molecular state, adsorption is more a function of the porosity of the carbon, principally the PSD of the microporosity. Extents of adsorption of a phenol are a maximum at neutral pH decreasing in both alkali and acidic solutions. At low values of pH, increased adsorption of protons on to the carbon surface reduces the facility of adsorption by the phenol. Also, the more polar is the... [Pg.411]

The general kinetic model [Eq. (23)] was used to qualitatively describe the effect of k , kd, and Cq on the extent of adsorption, namely F (or 6). Figure 1 shows F versus time for different values of kd for some fixed values of jS and Q. As can be seen from Fig. 1, although kd was significantly increased by three orders of magnitude, a maximum of a 20% decrease in F was found. The effect of initial concentration, Q, on F is depicted in Fig. 2. It is clearly seen that an... [Pg.855]

The nonylphenyl ethoxylates have also been used by Kayes and Rawlins in their work with diloxanide furoate and polystyrene latex [32]. Adsorption isotherms show the well-established trend with a maximum adsorbed concentration of NPEg of around 2/tmolg" and of NPE35 of about 0.35 mol Their results on the redispersibility of diloxanide suspensions, shown in Fig. 9.14, reflect therefore not the extent of adsorption of the surfactant molecules but their hydrophilic properties. The profiles can be compared with the corresponding sedimentation values for naphthalene and sulphathiazole above. [Pg.583]

Under conditions of surface saturation, the Gibbs equation can be used to determine the maximum extent of surfactant adsorption on the surface. The area occupied by a molecule, (expressed in nm ) can be calculated from the surface excess concentration F , of the saturated surface (mol/cm ) ... [Pg.110]

The standard deviation of the Gaussian zones expresses the extent of dispersion and corresponds to the width of the peak at 0.607 of the maximum height [24,25]. The total system variance (ofot) is affected by several parameters that lead to dispersion (Eq. 17.22). According to Lauer and McManigill [26] these include injection variance (of), longitudinal (axial) diffusion variance (of), radial thermal (temperature gradient) variance (of,), electroosmotic flow variance (of,), electrical field perturbation (electrodispersion) variance (of) and wall-adsorption variance (of ). Several authors [9,24,27-30] have described and investigated these individual variances further and have even identified additional sources of variance, like detection variance (erf,), and others... [Pg.589]


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Adsorption extent

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