Adsorption chemical: nature

Many solids have foreign atoms or molecular groupings on their surfaces that are so tightly held that they do not really enter into adsorption-desorption equilibrium and so can be regarded as part of the surface structure. The partial surface oxidation of carbon blacks has been mentioned as having an important influence on their adsorptive behavior (Section X-3A) depending on conditions, the oxidized surface may be acidic or basic (see Ref. 61), and the surface pattern of the carbon rings may be affected [62]. As one other example, the chemical nature of the acidic sites of silica-alumina catalysts has been a subject of much discussion. The main question has been whether the sites represented Brpnsted (proton donor) or Lewis (electron-acceptor) acids. Hall... 

In Section 1.3 it was noted that the energy of adsorption even for a perfect crystal differs from one face to another. An actual specimen of solid will tend to be microcrystalline, and the proportion of the various faces exposed will depend not only on the lattice itself but also on the crystal habit this may well vary amongst the crystallites, since it is highly sensitive to the conditions prevailing during the preparation of the specimen. Thus the overall behaviour of the solid as an adsorbent will be determined not only by its chemical nature but also by the way in which it was prepared. 

The incorporation of the new material without any increase in the overall length of the book has been achieved in part by extensive re-writing, with the compression of earlier material, and in part by restricting the scope to the physical adsorption of gases (apart from a section on mercury porosimetry). The topics of chemisorption and adsorption from solution, both of which were dealt with in some detail in the first edition, have been omitted chemisorption processes are obviously dependent on the chemical nature of the surface and therefore cannot be relied upon for the determination of the total surface area and methods based on adsorption from solution have not been developed, as was once hoped, into routine procedures for surface area determination. Likewise omitted, on grounds of... 

If an adsorbed chemical group (anchor) is more strongly bound to the surface than a solvent molecule would be at that site, an equiHbrium expression may be written for the displacement of solvent by adsorbate. Adsorption is particularly strong if the chemical nature of the adsorbed group is similar to that of the particle surface for example, in aqueous systems perfluoroalkane groups adsorb weU on polytetrafluoroethene particles and aromatic polyethene oxides adsorb weU on polystyrene. 

In the adsorption cycle, the wet inlet gas flows downward through the tower. The adsorbable components are adsorbed at rates dependent on their chemical nature, the size of their molecules, and the size of the pores. The water molecules are adsorbed first in the top layers of the desiccant bed. Dry hydrocarbon gases are adsorbed throughout the bed, As the upper layers of desiccant become saturated with water, the water in the wet gas stream begins displacing the previously adsorbed hydrocarbons in the lower desiccant layers. Liquid hydrocarbons will also be absorbed and will fill pore spaces that would otherwise be available for water molecules. 

It is noteworthy that even a separate treatment of the initial data on branched reactions (1) and (2) (hydrogenation of crotonaldehyde to butyr-aldehyde and to crotyl alcohol) results in practically the same values of the adsorption coefficient of crotonaldehyde (17 and 19 atm-1)- This indicates that the adsorbed form of crotonaldehyde is the same in both reactions. From the kinetic viewpoint it means that the ratio of the initial rates of both branched reactions of crotonaldehyde is constant, as follows from Eq. (31) simplified for the initial rate, and that the selectivity of the formation of butyraldehyde and crotyl alcohol is therefore independent of the initial partial pressure of crotonaldehyde. This may be the consequence of a very similar chemical nature of both reaction branches. 

A similar difference in the adsorption coefficients of the starting reactant of branched reactions was also found in the parallel dehydration and dehydrogenation of isopropyl alcohol on some oxide catalyst (123) here, of course, the chemical nature of both branches is clearly different. It is of interest, however, to note that for the series of catalysts with varying... 

The prepared MAC adsorbents were tested for benzene, toluene, 0-, m-, p-xylene, methanol, ethanol, iso-propanol, and MEK. The modified content of all MACs was 5wt% with respect to AC. The specific surface areas and amounts of VOC adsorbed of MACs prepared in this study are shown in Table 1. The amounts of VOC adsorbed on 5wt%-MAC with acids and alkali show a similar tendency. However, the amount of VOC adsorbed on 5wt%-PA/AC was relatively large in spite of the decrease of specific surface area excepting in case of o-xylene, m-xylene, and MEK. This suggests that the adsorption of relatively large molecules such as 0-xylene, m-xylene, and MEK was suppressed, while that of small molecules was enhanced. It can be therefore speculated that the phosphoric acid narrowed the micropores but changed the chemical nature of surface to adsorb the organic materials strongly. 

The IR spectra in Fig.7 indicate the preferential adsorption of NO on the Co sites. It may be conjectured that the Mo sulfide species are physically covered by the Co sulfide species or that Co-Mo mixed sulfide species are formed and the chemical natures of the Co and Mo sulfides are mutually modified. The Mo K-edge EXAFS spectra were measured to examine the formation of mixed sulfide species between Co and Mo sulfides. The Fourier transforms are presented in Fig.8 for MoSx/NaY and CoSx-MoSx/NaY. The structural parameters derived from EXAFS analysis are summarized in Table 1. The structure and dispersion of the Mo sulfides in MoSx/NaY are discussed above. With the Co-Mo binary sulfide catalyst, the Mo-Co bondings are clearly observed at 0.283 nm in addition to the Mo-S and Mo-Mo bondings. The Mo-Co distance is close to that reported by Bouwens et al. [7] for a CoMoS phase supported on activated carbon. Detailed analysis of the EXAFS results for CoSx-MoSx/NaY will be presented elsewhere. It is concluded that the Co-Mo mixed sulfides possessing Co-S-Mo chemical bondings are formed in CoSx-MoSx/NaY. 

The work function of charged particles found for a particular conductor depends not only on its bulk properties (its chemical nature), which govern parameter but also on the state of its surface layer, which influences the parameter (a) xhis has the particular effect that for different single-crystal faces of any given metal, the electron work functions have different values. This experimental fact is one of the pieces of evidence for the existence of surface potentials. The work function also depends on the adsorption of foreign species, since this influences the value of... 

It has been proven by experiment that there are donor acceptor atoms and molecules of absorbate and their classification as belonging to one or another type is controlled not only by their chemical nature but by the nature of adsorbent as well (see, for instance [18, 21, 203-205]). From the standpoint of the electron theory of chemisorption it became possible to explain the effect of electron adsorption [206] as well as phenomenon of luminescence of radical recombination during chemisorption [207]. The experimental proof was given to the capability of changing of one form of chemisorption into another during change in the value of the Fermi level in adsorbent [208]. 

Rippen, G., Ilgenstein, M., Klopffer, W., Poreniski, H.J. (1982) Screening of the adsorption behavior of new chemicals natural soils and model adsorbents. Ecotox. Environ. Saf. 6, 236-245. 

Gas-Liquid Chromatography. In gas-liquid chromatography (GLC) the stationary phase is a liquid. GLC capillary columns are coated internally with a liquid (WCOT columns) stationary phase. As discussed above, in GC the interaction of the sample molecules with the mobile phase is very weak. Therefore, the primary means of creating differential adsorption is through the choice of the particular liquid stationary phase to be used. The basic principle is that analytes selectively interact with stationary phases of similar chemical nature. For example, a mixture of nonpolar components of the same chemical type, such as hydrocarbons in most petroleum fractions, often separates well on a column with a nonpolar stationary phase, while samples with polar or polarizable compounds often resolve well on the more polar and/or polarizable stationary phases. Reference 7 is a metabolomics example of capillary GC-MS. 

The extent to which ions, etc. adsorb or experience an electrostatic ( coulombic ) attraction with the surface of an electrode is determined by the material from which the electrode is made (the substrate), the chemical nature of the materials adsorbed (the adsorbate) and the potential of the electrode to which they adhere. Adsorption is not a static process, but is dynamic, and so ions etc. stick to the electrode (adsorb) and leave its surface (desorb) all the time. At equilibrium, the rate of adsorption is the same as the rate of desorption, thus ensuring that the fraction of the electrode surface covered with adsorbed material is constant. The double-layer is important because faradaic charge - the useful component of the overall charge - represents the passage of electrons through the double-layer to effect redox changes to the material in solution. 

Where the protein microarray differed from the classic ELISA was in the much smaller quantities of proteins deposited on the substrate. While micrograms ( 1(P g) of protein are employed in the coating of an ELISA well, microarray spots may contain only picograms ( 10" g) or less of protein. The accurate delivery of small volumes [picoliters (pL) or nanoliters (nL)] containing small amormts of protein can be problematic. A certain amount of protein is likely to adsorb onto the quills or capillaries used for printing. The degree at which adsorption takes place is dependent upon a number of factors such as buffer composition, quill surface features and, more importantly, the physical and chemical nature of fhe protein itself. 

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