Ionization adsorption

Weisz assumption that, when equilibrium is attained, the energy of the adsorption traps is at the Fermi level, may not be valid in all cases. This assumption has the effect of removing the temperature dependence from the equilibrium adsorption. It is equivalent to the assumption that the number of empty adsorption traps is about equal to the number of ionized adsorption traps, and is invalid if empty adsorption traps are physically adsorbed atoms or molecules. For the latter case, A " in Fig. 5 will in general be greater than zero. 

Many properties of disperse systems are related to the distribution of charges in the vicinity of the interface due to the adsorption of electrolytes. The adsorption of molecules is driven by the van der Waals attraction, while the driving force for the adsorption of electrolytes is the longer-range electrostatic (Coulomb) interaction. Because of this, the adsorption layers in the latter case are less compact than in the case of molecular adsorption (i.e., they are somewhat extended into the bulk of the solution), and the discontinuity surface acquires noticeable, and sometimes even macroscopic thickness. This diffuse nature of the ionized adsorption layer is responsible for such important features of disperse systems as the appearance of electrokinetic phenomena (see Chapter V) and colloid stability (Chapters VII, VIII). Another peculiar feature of the adsorption phenomena in electrolyte solutions is the competitive nature of the adsorption in addition to the solvent there are at least two types of ions (even three or four, if one considers the dissociation of the solvent) present in the system. Competition between these ions predetermines the structure of the discontinuity surface in such systems -i.e. the formation of spatial charge distribution, which is referred to as the electrical double layer (EDL). The structure and theory of the electrical double layer is described in detail in textbooks on electrochemistry. Below we will primarily focus on those features of the EDL, which are important in colloid... 

Acids are preferentially adsorbed on alumina and magnesia, relative to adsorption on such nonbasic adsorbents as silica and Florisil. This is illustrated for alumina in Fig. 10-11, where the quantity Ag is plotted versus the pK value of the group i. Ag is equal to the experimental value of Q° (on alumina) minus the value calculated from a g value on silica (via Fig. 10-10). That is, Ag represents the preferential adsorption of the grewp i on alumina relative to silica. The dashed curve through the data of Fig. 10-11 is calculated [see Ref. (72)] on the basis of an ionization adsorption mechanism (proton transfer from sample to adsorbent) on... 

The previous sections dealt with processes of charge transport in electrically neutral electrolytes as applied to electrolytic and electrodialysis cells. Most substances, when at contact with a surrounding water (polar) medium, acquire a surface electric charge due to ionization, adsorption of ions, and dissociation [21, 22]. If the charged surface is placed into an electrolyte solution, then ions of the opposite sign (counter-ions) contained in the solution will be attracted to the surface, while ions of the same sign (co-ions) will be repelled from the surface (Fig. 7.7). 

The comparison of obtained data shows that at a given radius of aerosol particles of SAS solution, the rate adsorption constants of this aerosol at its adsorption from air are essentially higher than the rate adsorption constants from water bulk. This allows one to realize technically the flotation process using the close-pack ionized adsorption monolayer of surfactants, specially obtained at air bubble surface by aerosol dispersion and, thus, to control this process efficiently. 

Ecole Nationale Superieure du Petrole et des Moteurs Formation Industrie end point (or FBP - final boiling point) electrostatic precipitation ethyl tertiary butyl ether European Union extra-urban driving cycle volume fraction distilled at 70-100-180-210°C Fachausschuss Mineralol-und-Brennstoff-Normung fluid catalytic cracking Food and Drug Administration front end octane number fluorescent indicator adsorption flame ionization detector... 

Similarly, adsorption of ions (n+) onto a metal surface leads to a heat of adsorption of Q,. Generally, Q is about 2-3 eV and is greater than Q, which itself is about 1 eV. The difference between Q, and is the energy required to ionize neutrals (n ) on a metal surface so as to give ions (n+) or vice versa. This difference, Q - Q, can be equal to, greater than, or less than the difference, I - ( ), between the ionization energy (1) of the neutral and the ease with which a metal can donate or accept an electron (the work function, ( )). Where Q, - Q, > I - ( ), the adsorbed... 

Schematic diagram showing the development of a dipolar field and ionization on the surface of a metal filament, (a) As a neutral atom or molecule approaches the surface of the metal, the negative electrons and positive nuclei of the neutral and metal attract each other, causing dipoles to be set up in each, (b) When the neutral particle reaches the surface, it is attracted there by the dipolar field with an energy Q,. (c) If the values of 1 and <() are opposite, an electron can leave the neutral completely and produce an ion on the surface, and the heat of adsorption becomes Q,. Similarly, an ion alighting on the surface can produce a neutral, depending on the values of I and <(), On a hot filament the relative numbers of ions and neutrals that desorb are given by Equation 7.1,which includes the difference, I - <(), and the temperature, T,...

The carboxylated units, ionized, decrease adsorption on subterranean substrates (23), ia proportion to the number of units, an important parameter ia petroleum recovery processes. In waste treatment processes cationic acrylamide comonomer units are often used (31) to iacrease adsorption and thereby flocculation of soHds ia wastewater (see Acrylamide POLYMERS Flocculating agents). The favorable and characteristics of acrylamide facilitate the... 

Charge-Transfer Compounds. Similat to iodine and chlorine, bromine can form charge-transfer complexes with organic molecules that can serve as Lewis bases. The frequency of the iatense uv charge-transfer adsorption band is dependent on the ionization potential of the donor solvent molecule. Electronic charge can be transferred from a TT-electron system as ia the case of aromatic compounds or from lone-pairs of electrons as ia ethers and amines. 

If the pressure in the system is measured by an ionization gauge, the pumping speed SG of this gauge must be added to the pumping speed of the pump. In some cases it is necessary to take into account also the pumping speed Sw = —Fw w hich is due to the adsorption on the system walls and can even differentiate to some extent between the individual components. At the beginning of an experiment F0 = St and Fa0 = StP t/Pt. 

Alkali metals are strongly electropositive elements with low (2-3 eV) work function and low ionization potential. Upon adsorption on other metal surfaces they cause a severe (up to 3 eV) lowering of the metal work function, as already established by Langmuir in the early 1920 s. 

When one of the two acids is used in excess and the pk -values of the two acids differ strongly, the salt deficit method should be used with caution. Formic add, acetic acid, propionic acid, and trifluoroacetic acid have been electrolyzed competitively in mixtures of pairs. Formic acid and trifluoroacetic acid are comparable in case of electrolysis, both are more readily electrolyzed than acetic and propionic adds. Deviations are rationalized on the basis of differences in ionization [147]. It might 1 useful in such cases to neutralize both acids completely. Sometimes one of the two acids, although being the minor component, is more favorably oxidized possibly due to preferential adsorption or its higher acidity [148]. In this case the continuous addition of the more acidic add to an excess of the weaker acid may lead to successful cross-coupling [149], The chain length of the two acids should be chosen in such a... 

In a multiphase formulation, such as an oil-in-water emulsion, preservative molecules will distribute themselves in an unstable equilibrium between the bulk aqueous phase and (i) the oil phase by partition, (ii) the surfactant micelles by solubilization, (iii) polymeric suspending agents and other solutes by competitive displacement of water of solvation, (iv) particulate and container surfaces by adsorption and, (v) any microorganisms present. Generally, the overall preservative efficiency can be related to the small proportion of preservative molecules remaining unbound in the bulk aqueous phase, although as this becomes depleted some slow re-equilibration between the components can be anticipated. The loss of neutral molecules into oil and micellar phases may be favoured over ionized species, although considerable variation in distribution is found between different systems. 

In contrast to the ionizing electrode method, the dynamic condenser method is based on a well-understood theory and fulfills the condition of thermodynamic equilibrium. Its practical precision is limited by noise, stray capacitances, and variation of surface potential of the air-electrode surface, i.e., the vibrating plate. At present, the precision of the dynamic condenser method may be limited severely by the nature of the surfaces of the electrode and investigated system. In common use are adsorption-... 

Szabo S, Nagy F. 1978. Investigations of bismuth adsorption via the ionization of hydrogen adsorbed on platinized platinum in hydrochloric acid solutions. J Electroanal Chem 87 261-265. 

The properties of these systems depend strongly on the interfacial potentials created at the interface. They arise from oriented molecular dipoles, from ionization of the surfactant hydrophylic groups, and from the partition and adsorption of ions presented in the environment. 

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