Molecular size, of adsorbate

Commercial activated carbon has a very wide range of properties depending on the application. If the application is for gas phase separation, then the characteristics given in Table 1.2-3 is typical. For liquid phase applications, however, due to the large molecular size of adsorbate activated carbon used in such applications will possess larger mesopore volume and larger average pore radius for the ease of diffusion of molecules to the interior. 

In the case of mixtures of gases of different molecular size, an adsorbent of D > 2 will effect some segregation by size. This segregation will also affect the probability of bimolecular reactions between molecules of different sizes [168]. 

To obtain a reliable value of from the isotherm it is necessary that the monolayer shall be virtually complete before the build-up of higher layers commences this requirement is met if the BET parameter c is not too low, and will be reflected in a sharp knee of the isotherm and a well defined Point B. For conversion of into A, the ideal adsorptive would be one which is composed of spherically symmetrical molecules and always forms a non-localized film, and therefore gives the same value of on all adsorbents. Non-localization demands a low value of c as c increases the adsorbate molecules move more and more closely into registry with the lattice of the adsorbent, so that becomes increasingly dependent on the lattice dimensions of the adsorbent, and decreasingly dependent on the molecular size of the adsorbate. 

Zogorski et al. [125] indicate that external transport is the rate-limiting step in systems having poor mixing, dilute concentration of adsorbate, small particle sizes of adsorbent, and a high affinity of adsorbate for adsorbent. Some experiments conducted at low concentrations have shown that film diffusion solely controls the adsorption kinetics of low molecular weight substances [81,85]. 

Adsorption-desorption isotherms of toluene, p- and /n-xylene and mesitylene vapors by the sol-PILM and the modified product are compared in Figure 4. As anticipated, a decreasing tendency of uptake of each adsorbate is observed from sol-PILM to the final modified product due to the decrease in pore volume. It is also not surprised that the capacity of vapor adsorption by each sample decreases as the molecular size of the adsorbate increases, following the order ... 

Of course, the value of perfect crystal, there will be a regular variation of potential energy across the surface. It is not surprising to find that the most favourable site is at the centre of an array of surface atoms (cf. Figure 1.3). The corresponding depth of the potential energy well (at ze) will depend on the density and crystal structure of the adsorbent and the polarizability and molecular size of the adsorbate. 

Dynamic fluorescence anisotropy is based on rotational reorientation of the excited dipole of a probe molecule, and its correlation time(s) should depend on local environments around the molecule. For a dye molecule in an isotropic medium, three-dimensional rotational reorientation of the excited dipole takes place freely [10]. At a water/oil interface, on the other hand, the out-of-plane motion of a probe molecule should be frozen when the dye is adsorbed on a sharp water/oil interface (i.e., two-dimensional in respect to the molecular size of a probe), while such a motion will be allowed for a relatively thick water/oil interface (i.e., three-dimensional) [11,12]. Thus, by observing rotational freedom of a dye molecule (i.e., excited dipole), one can discuss the thickness of a water/oil interface the correlation time(s) provides information about the chemi-cal/physical characteristics of the interface, including the dynamical behavioiu of the interfacial structure. Dynamic fluorescence anisotropy measurements are thus expected... 

Three-Dimensional Model. On the other hand, if the interfacial layer is thick enough compared to the molecular size of SRIOI and if SRIOI molecules adsorbed on the interface are weakly oriented, the rotational motions of SRIOI take place in three dimensions, similar to those in a bulk phase. If this is the case, the contribution of the fluorescence with the excited dipole moment of SR 101 directed along the z-axis cannot be neglected, so that the time profile of the total fluorescence intensity must be proportional to / (0 + 2/i(t). Thus, fluorescence dynamic anisotropy is given by Equation (15), as is well known for that in a macroscopically isotropic system [10,13] ... 

DW in Table 12.1). Therefore, the interfacial layer of the water/DCE interface is thick compared to the molecular size of SR 101, and the dye molecules adsorbed on the interface are weakly oriented. Otherwise, the interface is spatially rough at the molecular size of SRlOl. SRlOl molecules at the water/DCE interface behave similar to those in an isotropic medium, in contrast to the results at the water/CCU interface. 

A novel and simple method for determination of micropore network connectivity of activated carbon using liquid phase adsorption is presented in this paper. The method is applied to three different commercial carbons with eight different liquid phase adsorptives as probes. The effect of the pore network connectivity on the prediction of multicomponent adsorption equilibria was also studied. For this purpose, the Ideal Adsorbed Solution Theory (lAST) was used in conjuction with the modified DR single component isotherm. The results of comparison with experimental data show that incorporation of the connectivity, and consideration of percolation processes associated with the different molecular sizes of the adsorptives in the mixture, can improve the performance of the lAST in predicting multicomponent adsorption equilibria. 

The MSC membranes are produced by carbonization of PAN, polymide, and phenolic resins. They contain nanopores, which allow some of the molecules of a feed gas mixture to enter the pore structure at the high pressure side, adsorb, and then diffiise to the low pressure side of the membrane, while excluding the other molecules of the feed gas. Thus, separation is based on the difference in the molecular sizes of the feed gas components. The smaller molecules preferentially diffuse through the MSC membrane as shown by Table 4 [16,17]. 

It is easy to see that adsorption energies are dependent on the curvature of the interface. Consider first adsorption on a planar interface. At low pressures, p, a sub-monolayer, gas-like, and eventually a two-dimensional liquid described by a Langmuir isotherm (or decorations thereof) forms. At higher pressures still (p/ps>0.35, where ps is the saturated vapour pressure) multilayer adsorption isotherms can occur depending on adsorbate, molecular size and adsorbate-substrate interactions. This regime is usually described by the theory of Brxmauer-Emmet-Teller (BET). In this domain, ln(p/pg) = 1/t, where t is the thickness of the film. 

The effect on adsorption of the fixation of oxygen surface complexes is shown in Table 8. In addition to the decrease in V stated before, the adsorption is less energetic after the treatment [28-30] because partial blocking of the pores hinders the access of pores with similar dimension to the molecular size of the adsorbates. Moreover, it is interesting to point out that benzene is adsorbed more strongly on the original than on the oxidized... 

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