Adsorption from solution effect

A recent design of the maximum bubble pressure instrument for measurement of dynamic surface tension allows resolution in the millisecond time frame [119, 120]. This was accomplished by increasing the system volume relative to that of the bubble and by using electric and acoustic sensors to track the bubble formation frequency. Miller and co-workers also assessed the hydrodynamic effects arising at short bubble formation times with experiments on very viscous liquids [121]. They proposed a correction procedure to improve reliability at short times. This technique is applicable to the study of surfactant and polymer adsorption from solution [101, 120]. 

Chromatography is based upon the selective adsorption from solution on the active surface of certain finely divided solids. Closely related substances exhibit different powers of adsorption, so that separations, which are extremely difficult by ordinary chemical methods, may be effected by this means. When, for example, a solution of leaf pigments... 

Adsorption of ions from the solution. There are two types of ionic adsorption from solutions onto electrode surfaces an electrostatic (physical) adsorption under the effect of the charge on the metal surface, and a specific adsorption (chemisorption) under the effect of chemical (nonelectrostatic) forces. Specifically adsorbing ions are called surface active. Specific adsorption is more pronounced with anions. 

In the case of adsorption from solution, the surfactant layers are in equilibrium with the solution and will de-sorb on dilution. However, it would be very useful to produce adsorbed layers in both air and water, which will remain adsorbed. This can be achieved using the Langmuir-Blodgett deposition technique. The technique is based on the observation that if a surfactant, which is insoluble in water, is dissolved in a volatile, non-aqueous solvent and then spread on water, an insoluble monolayer of orientated surfactant molecules will remain at the air/solution interface. The effect of the spreading surfactant and its surface film pressure can be dramatically demonstrated by spreading hydrophobic talc powder on a clean water surface and then placing a... 

In the rest of this section, the various ways transients can be used to reduce diffusion effects and the effects of contamination of the electrode surface by adsorption from solution will be discussed, as well as any counter-limitations that some types of transient measurements may involve. 

Both adsorption from solution and micellization occur as a result of the hydrophobic effect. To test the correspondence between these two effects. Rosen assembled AG° values for adsorption at the air-water interface and for micellization of a number of linear and branched surfactants. The following is a selection of these data ... 

In addition to film preparation by adsorption from the melt, Compound D was also adsorbed on pure platinum surfaces by adsorption from solution in nitrobenzene, ethyl alcohol, and ethyl alcohol-water solutions. As was true of films adsorbed on chromium, adsorption on platinum from solution resulted in surface coatings exhibiting lower contact angles than those formed from the molten acid. The same postadsorption treatments were also effective in increasing the contact angles of films of Compound D on platinum. 

Studies of molecular adsorption from solution at well-defined solid surfaces is yielding important results. Well-defined surfaces have a simplifying effect on such studies by eliminating many of the structural imperfections which would otherwise complicate the results with a mixutre of adsorption states. Surface analysis methods such as LEED, Auger spectroscopy, EELS, XPS and voltammetry are very well suited to the characterization of surface molecular structure, composition, and bonding. As a result, clear correlations between adsorbed state and surface chemical or electrochemical reactivity are beginning to emerge. 

The extent of adsorption can have a profound effect on the rate of the surface reaction. Equilibrium isotherms of many kinds have been reported for adsorption from solution and have been classified by Giles et al. [24-27], The shapes of these adsorption curves often furnish qualitative information on the nature of the solute-surface interactions. Several of the types of isotherm observed in dilute solution are represented reasonably well by three simple and popular isotherm equations, those of Henry, Langmuir, and Freundlich. Their shapes are illustrated in Fig. 1. Each of these isotherms relates the surface concentrations cads (mol m"2) to the bulk equilibrium concentration c of the solute species in question. When few surface sites are occupied, Henry s law adsorption... 

The area is an important surface parameter for catalytic studies. It is needed to evaluate the rate constant of the surface reaction from the kinetics as well as to allow a fair comparison to be made of the effectiveness of different catalysts. Areas are commonly determined by nitrogen or krypton gas adsorption interpreted by the Brunauer-Emmett Teller (BET) isotherm [30, 32], A number of other methods has been proposed and utilised including microscopy, isotopic exchange, chromatography, gas permeability, adsorption from solution, and negative adsorption (desorption) of co-ions [30, 33]. 

Eltekov, Pavlova, Shikalova, Bogacheva and co-workers (Moscow State University Institute of Physical Chemistry, the U.S.S.R. Academy of Sciences, Moscow) (17, 290, 297-307) investigated the effect of the chemical nature and the dimensions of the pores in silica adsorbents on the adsorption from solutions. The adsorption of benzene from n-hexane solutions on silica gels with a hydroxylated and a dehydroxylated surface was studied. Dehydroxylation sharply lowered the heat of adsorption of benzene. A comparison was made of the adsorption isotherms for a series of n-hexane solutions of aromatic hydrocarbons on hydroxylated silica gel. The intermolecular interaction of aromatic hydrocarbons with this adsorbent is stronger than the interaction of saturated hydrocarbons because aromatic hydrocarbons form hydrogen bonds with the silanol groups on the SiC>2 surface. 

The adsorption from solutions on finely dispersed powders and porous adsorbents is used for the removal of dissolved toxic components, as well as for concentrating and entrapping valuable substances from dilute solutions. In agreement with the polarity equalization rule, surface active substances dissolved in aqueous medium can be removed by adsorption on non-polar adsorbents (such as activated carbon), or on adsorbents that are capable of chemisorbing the surfactant polar heads. In order to increase the effectiveness... 

This figure illustrates the effect in the case of adsorption from the vapour phase. For adsorption from solution where there is competition between the adsorption of solute and solvent the picture is slightly more complicated, but the outcome is similar. 

Very straightforward effects of surface chemistry of carbons are seen on the adsorption from solutions of aromatics [10-17], dyes [18], heavy metals [19-24], pharmaceuticals [25-27], polar species such as alcohols [28-30], acids or aldehydes [31,32], and even small-molecule gases [33,34]. In those applications the species present on the carbon surface can enhance the specific interactions or even alter the porosity via blocking of pore entrances for molecules to be adsorbed. Specific interactions include hydrogen bonding, acid-base, and complexation. 

The size effects come from the fact that the adsorbed solute molecules have greater dimensions than those of the solvent molecules. The adsorption from solution is in fact a replacement process, during... 

The effect of adsorption loading procedures described earlier (adsorption from solution and IWI) was also investigated. A fast and complete release of the supported IL was obtained when the adsorption from solution loading was used. 

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