Adsorption modifiers

Last time development of methods of iodine determination, which include preliminary sorption preconcentration of microcomponents and their subsequent determination in phase of concentrate get great practical significance. Silica gel (SG) with adsorptively modified quaternary ammonium salts (QAS) gets properties of anion-exchange resin. The sorbents modified in this way can be used successfully for determination of different anions. 

One structural parameter of potential interest in the adsorption of simple diatomic molecules, such as CO, NO and N2, is the intramolecular bondlength. Much of the motivation for studying such adsorbates is related to the way adsorption modifies the chemistry of these species as the basis for heterogeneous catalysis. Many such reactions involve scission of the intramolecular bond, and if the adsorption is of the... 

FIGURE 6.1 Factors that influence the nature of electrostatic cation adsorption at oxide surfaces, and thus, PL membrane structure, (a) Percentage of surface sites occupied by TMA+ ions compared to Na+ ions. This number is another way of representing AGexcTMA+/Na+. (b) Standard state entropy of cation adsorption. (Modified and reprinted from Sahai, N., J. Colloid Interface Sci., 252, 309, copyright 2002, and Sahai, N., Geochim. Cosmochim. Acta, 64, 3629, copyright 2000. With permission from Elsevier Science.)... 

The third class involves electroactive adsorbed species, yet it also encompasses the case in which, although originally inactive, the species is activated or modified in the adsorption process to give rise to the formation of electroactive adsorbed molecules. Obviously, all these effects discussed for the two previous classes are observed for this class, but additional effects are observed for the adsorbed species itself. Indeed, adsorption modifies (1) the concentration of the species at the electrode surface vis-a-vis that predicted from its bulk concentration, and (2) the energetics of the electron transfer reaction. The latter point arises because of additional thermodynamic contributions to be considered in the Rq/Ro or Po/P equilibria in Scheme 5 and also from changes in the reorganization energies. The former point leads to a variety of behaviors, since it is obviously a function of the kinetics of adsorption-desorption phenomena. A third additional effect of electroactive adsorbed species arises from their possible ability to act as electron transfer med-... 

Figure 1335 Apparent K i values for Np(V) as a function of Eh with INp = 10 M. Sorbent sediments contained quartz, K-feldspar, plagioclase feldspar, kaolinite, muscovite, calcite, chlorite, and dolomite. Apparent Kj values from >10 to > lO, measured for Eh values below about 250 mV, reflect precipitation of Np(IV) solids rather than adsorption. Modified after Lieser and Mohlenweg, Neptunium in the hydrosphere and in the geosphere. Radiochim. Acta 43 27-35. Copyright 1988 by Oldenbourg Verlag GmbH. Used by permission.

TIRF Protein adsorption Modified proteins are required, fluorescence-based techitique... 

In the field of adsorption from solution, many discussions and reviews were published about the measurement of the adsorbed amount and the presentation of the corresponding data [14, 45—47]. Adsorption isotherms are the first step of any adsorption study. They are generally determined from the variation of macroscopic quantities which are rigorously measurable far away from the surface (e.g., the concentration of one species, the pressure, and the molar fraction). It is then only possible to compare two states with or without adsorption. The adsorption data are derived from the difference between these two states, which means that only excess quantities are measurable. Adsorption results in the formation of a concentration profile near an interface. Simple representations are often used for this profile, but the real profile is an oscillating function of the distance from the surface [15, 16]. Without adsorption, the concentration should be constant up to the soHd surface. Adsorption modifies the concentration profile of each component as well as the total concentration profile. It must be noted also that when the liquid is a pure component its concentration profile, i.e., its density, is also modified. Experimentally, the concentration can be measured at a large distance from the surface. The surface excess of component i is the... 

The chemical modification of a polymer through phosphorus incorporation may impart new properties to the material, like inereased solubility, heavy metal ion adsorption, modified glass transition temperature, and flame retardancy. Much work has been done over several decades and especially in the past 15 years to overcome the poor fire behavior of polymers by incorporating phosphorus into the maeromolecular structure through covalent bonding. 

We have to remember that the isotherm equation was derived based on the assumption that the adsorbate is inert and is not modified upon adsorption. This assumption is not broadly valid and we know that adsorption modifies the surface to a significant extent. However, for all practical purposes, the Gibbs isotherm equation and the isotherms we will derive from it provide practical equations. 

Surface modification by polymers is an effective method of enhancing polymer-clay compatibility. There are two mechanisms for surface modification of clay minerals with polymers (i) physical adsorption and (ii) chemical grafting of functional polymers onto the clay surface. Physical adsorption modifies the surface properties of clay, but the structure of the clay mineral is preserved. However, the forces between the adsorbed molecules and the clay mineral might be weak, causing desorption. Grafting of functional polymers onto the surfaces of clay minerals provides stronger clay-polymer interaction and permits control... 

Dye assistants, antistatic agent additives, waste-water flocculants, sizing, lubricants, fabric heat-adsorption modifiers, phase-transformation fabric... 

As discussed in Chapter III, the progression in adsoiptivities along a homologous series can be understood in terms of a constant increment of work of adsorption with each additional CH2 group. This is seen in self-assembling monolayers discussed in Section XI-IB. The film pressure r may be calculated from the adsorption isotherm by means of Eq. XI-7 as modified for adsorption from dilute solution ... 

An adsorbed film obeys a modified Amagat equation of state, t(t = qkT (see Eq. ni-107). Show that this corresponds to a Freundlich adsorption isotherm (Eq. XI-12) and comment on the situation. 

The following derivation is modified from that of Fowler and Guggenheim [10,11]. The adsorbed molecules are considered to differ from gaseous ones in that their potential energy and local partition function (see Section XVI-4A) have been modified and that, instead of possessing normal translational motion, they are confined to localized sites without any interactions between adjacent molecules but with an adsorption energy Q. 

The rate of physical adsorption may be determined by the gas kinetic surface collision frequency as modified by the variation of sticking probability with surface coverage—as in the kinetic derivation of the Langmuir equation (Section XVII-3A)—and should then be very large unless the gas pressure is small. Alternatively, the rate may be governed by boundary layer diffusion, a slower process in general. Such aspects are mentioned in Ref. 146. 

The adsorption isotherms are often Langmuirian in type (under conditions such that multilayer formation is not likely), and in the case of zeolites, both n and b vary with the cation present. At higher pressures, capillary condensation typically occurs, as discussed in the next section. Some N2 isotherms for M41S materials are shown in Fig. XVII-27 they are Langmuirian below P/P of about 0.2. In the case of a microporous carbon (prepared by carbonizing olive pits), the isotherms for He at 4.2 K and for N2 at 77 K were similar and Langmuirlike up to P/P near unity, but were fit to a modified Dubninin-Radushkevich (DR) equation (see Eq. XVII-75) to estimate micropore sizes around 40 A [186]. 

There are a few other surface-sensitive characterization techniques that also rely on the use of lasers. For instance surface-plasmon resonance (SPR) measurements have been used to follow changes in surface optical properties as a fiinction of time as the sample is modified by, for instance, adsorption processes [ ]. SPR has proven usefiil to image adsorption patterns on surfaces as well [59]. 

Jordan C E and Corn R M 1997 Surface piasmon resonance imaging measurements of eiectrostatic biopoiymer adsorption onto chemicaiiy modified goid surfaces Ana/. Chem. 69 1449-56... 

Chinn J A, Horbett T A, Ratner B D, Sohway M B, Hague Y and Hausohka S D 1989 Enhanoement of serum fibroneotin adsorption and the olonal plating of swiss mouse-3T3 fibroplast and MM14-mouse myoblast sells on polymer substrates modified by radiofrequenoy plasma deposition J. Colloid Interface Sol. 127 67-87... 

Fig. 3.24 Test of the tensile strength hysteresis of hysteresis (Everett and Burgess ). TjT, is plotted against — Tq/Po where is the critical temperature and p.. the critical pressure, of the bulk adsorptive Tq is the tensile strength calculated from the lower closure point of the hysteresis loop. C), benzene O. xenon , 2-2 dimethyl benzene . nitrogen , 2,2,4-trimethylpentane , carbon dioxide 4 n-hexane. The lowest line was calculated from the van der Waals equation, the middle line from the van der Waals equation as modified by Guggenheim, and the upper line from the Berthelot equation. (Courtesy Everett.)...

The strength of dispersion interaction of a solid with a gas molecule is determined not only by the chemical composition of the surface of the solid, but also by the surface density of the force centres. If therefore this surface density can be sufficiently reduced by the pre-adsorption of a suitable substance, the isotherm may be converted from Type II to Type III. An example is rutile, modified by the pre-adsorption of a monolayer of ethanol the isotherm of pentane, which is of Type II on the unmodified rutile (Fig. 5.3, curve A), changes to Type III on the treated sample (cf. Fig. 5.3 curve B). Similar results were found with hexane-l-ol as pre-adsorbate. Another example is the pre-adsorption of amyl alcohol on a quartz powder... 

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