Ion-exchange mechanisms

Over a number of years, fuel cells have promised a new way to generate electricity and heat from fossil fuels using ion-exchange mechanisms. Fuel cells are... 

The complexing affinity may cause penetration of anions into the oxide by some ion exchange mechanism. The presence of such species inside the oxide may have a profound effect on its conductivity. 

A thorough study on the ion-exchange mechanism and the effect of distinct counterions in this PO mode was recently presented by Gyimesi-Forras et al. [41]. A large variety of distinct acid additives to methanol, acetonitrile, and tetrahydrofuran (Table 1.1) (without any base added) was investigated in view of the stoichiometric displacement model and their effect on the enantiomer separation of 2-methoxy-2-(l-naphthyl)propionic acid. The stoichiometric displacement model (Equation 1.1) was obeyed also in the PO mode, as revealed by linear plots of log k vs. acid concentration. The slopes and intercepts along with the concentration ranges used with the distinct competitor acids are summarized in Table 1.1. 

The experimental data conformed to Eq. (93) and therefore could be interpreted by either mechanism I or II data analysis showed no linear dependence of the logarithm of parameter C in Eq. (93).on the carbon number of the alkyl sulfate hetaerons. However, in the case of dynamic ion exchange parameter C is the binding constant of the hetaeron to the stationary phase hnd its logarithm should be linearly dependent on the carbon number of the alkyl moiety. Even if the results of this study are not accepted as support for ion-pairing (mechanism I) uniquely, they cannot be used to validate dynamic ion-exchange (mechanism II) either. 

As shown in Fig. 53 for the case of ion-pairing in the eluent and dynamic ligand exchange without expulsion, the addition of organic solvent will increase and decrease the retention factor at relatively low and high hetaeron concentration, and this is shown by points A and B, respectively. The opposite pattern obtains in the case of the dynamic ion-exchange mechanism, of course. At intermediate hetaeron concentrations... 

The catalyst is actually hydroxyl ion, which crosses the membrane by an ion-exchange mechanism on being brought into contact with the aqueous solution... 

The ion-exchange mechanism of exfracfion does nof occur only for amino acids. We observed if also for cafecholamines [26]. These compounds are efficiently extracted into ILs in the cationic form, af pH 1-8. Af fhese pH, the primary (dopamine) or secondary (adrenaline and dobutamine) amino groups are protonated (catecholamines are oxidized in alkaline solutions at pH > 8). By analogy with amino acids, extraction may be described by the cation-exchange reaction ... 

W. Holl, Optical verification of ion exchange mechanisms in weak electrolyte resins, Reactive Polymers, 2 (1984), p. 93. 

In view of the fact that no hafnium is present in the unhydrolyzed form under any of the conditions given in Table II, the ion exchange mechanism of adsorption by glass may be disregarded. This is substantiated by the fact that a different treatment of the glass had no effect upon its adsorption capacity for hafnium. This is similar to the results of Starik and Rozovskaya who found small effects upon the adsorptivity of hydrolyzed ions caused by glass modification even when drastic treatment... 

Anions are nominally too large to be injected down channels in the semiconductor. However, under strong anodic bias there may be electrochemical interactions of the anions with the semiconductor surface (possibly by an ion exchange mechanism). 

Recently, Bartels and Arends113 studied the adsorption of poly(4-vinylpyridinium fluoride) with different hexadecyl group content on hydroxyapatite. Adsorbance decreased as the hexadecyl content, i.e. the charge density, was increased. Desorption experiments showed that the adsorption of this polyelectrolyte in water is essentially irreversible. However, the polymer partially desorbed when excess calcium ions were added. Bartels and Arends concluded that adsorption of poly(4-vinylpyridinum fluoride) occurs as a result of the uptake of fluoride ions by hydroxyapatite which releases phosphate ions into water. They also suggested that this adsorption phenomenon can be interpreted in terms of an ion-exchange mechanism. 

Figure 9. Schematic of four mechanisms describing the interaction of Ca with films of DPL (1) ionr-dipole interaction (2) ion-exchange mechanism (3) ionr-ion interaction with ionized anionic lipid contaminant and (4) penetration of electrolyte, HgO, and derived ions into the air- vater or the lipid-water interface. A highlight of Mechanism 4 (consistent with the surface radioactivity data, Ref. 3) is the adsorption of the ions of HCl resulting from th ehydrolysis of CaCU. The coexistence of Ca(OH) and aqueous HCl at the interface requires the formation of compartments or pools that permit the separation of the acid from the base. Such a coexistence of acidic and basic pools is conceivable in the light of the Ca(OH), film on the HCl solution following the hydrolysis of CaCU in the absence of DLP films and is probably a characteristic of DPL films, since the adsorption of Cl was nil without DPL.

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