Adsorption names

Solution The slopes of these lines are identical (within experimental error), and the combination of Equations (40) and (7.72) shows that the reciprocal of the slope gives the adsorption at saturation. We conclude, therefore, that all three isotherms converge to the same saturation level of adsorption, namely, (2.0) 1 = 0.50 g g -1. 

Equation (89) includes, as a particular case, the process of adsorption, namely when B is absent and I coincides with A. In this case (90) and (91) are identical. 

Also the choice of the electrostatic model for the interpretation of primary surface charging plays a key role in the modeling of specific adsorption. It is generally believed that the specific adsorption occurs at the distance from the surface shorter than the closest approach of the ions of inert electrolyte. In this respect only the electric potential in the inner part of the interfacial region is used in the modeling of specific adsorption. The surface potential can be estimated from Nernst equation, but this approach was seldom used In studies of specific adsorption. Diffuse layer model offers one well defined electrostatic position for specific adsorption, namely the surface potential calculated in this model can be used as the potential experienced by specifically adsorbed ions. The Stern model and TLM offer two different electrostatic positions each, namely, the specific adsorption of ions can be assumed to occur at the surface or in the -plane. 

There is a further difficulty about the reversible, sluggish final adsorption, namely that the bleaching of the color was not likewise reversed on pumping off the ca. 5% of hydrogen. This could be explained by the existence of some reversible hydrogen-adsorbing site other than color in about 5% of the abundance of color, and of a similar concentration... 

Replacing in eq. (11.18) concentrations with adsorption using the eq. (11.22), one may obtain the relationship between the two-dimensional pressure and the adsorption, namely... 

CO on Pt(lll)/Ru surface alloys has also been recentiy studied by SFG [77]. In contrast to the bulk alloy, CO adsorbed on the surface alloy exhibits two peaks one at 2073 cxn and one at 2000 cm , which are interpreted as originating from two distinct sites for CO adsorption, namely the atop sites of atoms of Pt and Ru, respectively. Thus the CO molecules on this surface are distinct and vibrationaUy uncoupled, an effect likely due to the large domains of Ru islands in the surface alloy, in contrast to the bulk alloy material. 

The mechanism of inhibition action by organic compounds is adsorption. There are two types of adsorption, namely, physiosorption and chemisorption. For physiosorption, corrosion inhibition may be a result of the formation of mechanical barriers by inhibitor species. This will hinder the movement of ionic species from and to the surface of the corroding metal. On the other hand, for chemisorption, the chemical reaction takes place on the surface of the corroding metal, with subsequent formation of a thin coating. This hinders movement of species to and from the corroding surface as well. The characteristics of physiosorption are as follows ... 

In spite of this, there is no accurate description accounting for the formation of a liquid film at the surface of a solid starting from an adsorbed film, or conversely of the appearance of an adsorbed film in the final stages of evaporation of a liquid film. In fact, the two major models hitherto developed for multilayer adsorption, namely the model originally proposed by Brunauer, Emmett and Teller (BET) and the one proposed separately by Frenkel, Halsey and Hill (FHH), apply to the description of a thin adsorbed phase the former and of a liquid film the latter. 

The materials included in this study are listed in Fig. 1 b. Two of the materials studied consist of two interpenetrated networks IRMOF-9 and lRMOF-15 are the interpenetrated forms of IRMOF-10 and IRMOF-16 respectively (see Fig. 1 c). Intopenetration results in two opposite effects for adsorption, namely a gain in surface area and stronger en getic interactions between the sorbate molecules and the framework but also a loss of porosity and an increase in the crystal density which affects the gravimetric uptake negatively. 

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... 

Let us consider the simplest surface that shows ion-specific adsorption, namely the water-air interface. In a by now classical series of papers, Jungwirth and co-workers have shown that iodide ions do adsorb at the air-water interface, in strong contrast with the traditional view. Those simulations were performed with polarisable force fields, while the non-polarisable force fields employed at that time did not show adsorption of iodide. It was concluded that the polarisability plays a dominant role in the adsorption mechanism. Let us reconsider that problem using our novel thermodynamically optimised force fields discussed in the earlier section. We show results for the potential of mean force of a single ion at an air-water interface, calculated using umbrella sampling and the WHAM method. ... 

These concluding chapters deal with various aspects of a very important type of situation, namely, that in which some adsorbate species is distributed between a solid phase and a gaseous one. From the phenomenological point of view, one observes, on mechanically separating the solid and gas phases, that there is a certain distribution of the adsorbate between them. This may be expressed, for example, as ria, the moles adsorbed per gram of solid versus the pressure P. The distribution, in general, is temperature dependent, so the complete empirical description would be in terms of an adsorption function ria = f(P, T). 

As also noted in the preceding chapter, it is customary to divide adsorption into two broad classes, namely, physical adsorption and chemisorption. Physical adsorption equilibrium is very rapid in attainment (except when limited by mass transport rates in the gas phase or within a porous adsorbent) and is reversible, the adsorbate being removable without change by lowering the pressure (there may be hysteresis in the case of a porous solid). It is supposed that this type of adsorption occurs as a result of the same type of relatively nonspecific intermolecular forces that are responsible for the condensation of a vapor to a liquid, and in physical adsorption the heat of adsorption should be in the range of heats of condensation. Physical adsorption is usually important only for gases below their critical temperature, that is, for vapors. 

The preceding derivation, being based on a definite mechanical picture, is easy to follow intuitively kinetic derivations of an equilibrium relationship suffer from a common disadvantage, namely, that they usually assume more than is necessary. It is quite possible to obtain the Langmuir equation (as well as other adsorption isotherm equations) from examination of the statistical thermodynamics of the two states involved. 

Figure Bl.22.1. Reflection-absorption IR spectra (RAIRS) from palladium flat surfaces in the presence of a 1 X 10 Torr 1 1 NO CO mixture at 200 K. Data are shown here for tluee different surfaces, namely, for Pd (100) (bottom) and Pd(l 11) (middle) single crystals and for palladium particles (about 500 A m diameter) deposited on a 100 A diick Si02 film grown on top of a Mo(l 10) single crystal. These experiments illustrate how RAIRS titration experiments can be used for the identification of specific surface sites in supported catalysts. On Pd(lOO) CO and NO each adsorbs on twofold sites, as indicated by their stretching bands at about 1970 and 1670 cm, respectively. On Pd(l 11), on the other hand, the main IR peaks are seen around 1745 for NO (on-top adsorption) and about 1915 for CO (tlueefold coordination). Using those two spectra as references, the data from the supported Pd system can be analysed to obtain estimates of the relative fractions of (100) and (111) planes exposed in the metal particles [26].

Figure Bl.22.3. RAIRS data in the C-H stretching region from two different self-assembled monolayers, namely, from a monolayer of dioctadecyldisulfide (ODS) on gold (bottom), and from a monolayer of octadecyltrichlorosilane (OTS) on silicon (top). Although the RAIRS surface selection rules for non-metallic substrates are more complex than those which apply to metals, they can still be used to detemiine adsorption geometries. The spectra shown here were, in fact, analysed to yield the tilt (a) and twist (p) angles of the molecular chains in each case with respect to the surface plane (the resulting values are also given in the figure) [40].

Figure Bl.22.6. Raman spectra in the C-H stretching region from 2-butanol (left frame) and 2-butanethiol (right), each either as bulk liquid (top traces) or adsorbed on a rough silver electrode surface (bottom). An analysis of the relative intensities of the different vibrational modes led to tire proposed adsorption structures depicted in the corresponding panels [53], This example illustrates the usefiilness of Raman spectroscopy for the detennination of adsorption geometries, but also points to its main limitation, namely the need to use rough silver surfaces to achieve adequate signal-to-noise levels.

On standing, gelatinous aluminium hydroxide, which may initially have even more water occluded than indicated above, is converted into a form insoluble in both acids and alkalis, which is probably a hydrated form of the oxide AI2O3. Both forms, however, have strong adsorptive power and will adsorb dyes, a property long used by the textile trade to dye rayon. The cloth is first impregnated with an aluminium salt (for example sulphate or acetate) when addition of a little alkali, such as sodium carbonate, causes aluminium hydroxide to deposit in the pores of the material. The presence of this aluminium hydroxide in the cloth helps the dye to bite by ad sorbing it—hence the name mordant (Latin mordere = to bite) dye process. 

In the present study we try to obtain the isotherm equation in the form of a sum of the three terms Langmuir s, Henry s and multilayer adsorption, because it is the most convenient and is easily physically interpreted but, using more a realistic assumption. Namely, we take the partition functions as in the case of the isotherm of d Arcy and Watt [20], but assume that the value of V for the multilayer adsorption appearing in the (5) is equal to the sum of the number of adsorbed water molecules on the Langmuir s and Henry s sites ... 

For the more advanced student, we have extended the section on Quantitative Semi-micro Analysis, and we have included a section dealing with Special Techniques in Separation and Purification, namely Adsorption Chromatography, Paper Chromatography, and Ion- Exchange Processes. 

The forces which bring about adsorption always include dispersion forces, which are attractive, together with short-range repulsive forces. In addition, there will be electrostatic (coulombic) forces if either the solid or the gas is polar in nature. Dispersion forces derive their name from the close connection between their origin and the cause of optical dispersion. First... 

Fig. 2.17 The adsorption of pentane on different adsorbents, (a) Effect of the nature of the adsorbent on the shape of the isotherm (each isotherm is labelled with the name of the adsorbent), (b) Dependence of ajpentane) on the value of parameter C. (Courtesy Kiselev and Eltekov. )...

Despite the difference ia the nature of the surface, the adsorptive behavior of the molecular sieve carbons resembles that of the small pore zeoHtes. As their name implies, molecular sieve separations are possible on these adsorbents based on the differences ia adsorption rate, which, ia the extreme limit, may iavolve complete exclusion of the larger molecules from the micropores. 

Other Fiber Evaluation Methods. The extent of fiber separation (fiber openness) is an important evaluation criteria that is commonly measured by several techniques, namely ak permeabiUty, adsorbed gas volume, bulk density, and residence (compression and recovery). The adsorption and retention of kerosene is also used as a measure of fiber openness and fiber adsorption capacity (34). 

The stmcture of activated carbon is best described as a twisted network of defective carbon layer planes, cross-linked by aHphatic bridging groups (6). X-ray diffraction patterns of activated carbon reveal that it is nongraphitic, remaining amorphous because the randomly cross-linked network inhibits reordering of the stmcture even when heated to 3000°C (7). This property of activated carbon contributes to its most unique feature, namely, the highly developed and accessible internal pore stmcture. The surface area, dimensions, and distribution of the pores depend on the precursor and on the conditions of carbonization and activation. Pore sizes are classified (8) by the International Union of Pure and AppHed Chemistry (lUPAC) as micropores (pore width <2 nm), mesopores (pore width 2—50 nm), and macropores (pore width >50 nm) (see Adsorption). 

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