Adsorption edge

Stdhr J and Jaeger R 1982 Adsorption-edge resonances, core-hole screening and orientation of chemisorbed molecules CO, NO and N2 on Ni(IOO) Rhys. Rev. B 26 4111-31... 

Band gap energies of the catalysts were calculated from adsorption edge wavelength... 

The macroscopic proton coefficient may be determined by graphical analysis of observed system variables according to two different procedures fractional adsorption edge linearization (6) and isotherm analysis (7 ). The procedures for calculating the macroscopic proton coefficients according to these two methods are discussed in detail below, as are their relative advantages and disadvantages for use in semi-empirical descriptions of adsorption. 

This combined dependency of xD on pH and surface coverage has the net effect of decreasing the slope of the pH-fractional adsorption edge as the ratio of adsorbate to adsorbent sites increases, as in Figure 3a. 

As a second example, consider the partitioning of Cd(II) between two adsorbents—a-TiC and (am)Fe20j.H20. Figure 11 shows Cd(II) fractional adsorption as a function of pH for binary mixtures of these adsorbents under experimental conditions such that Cddl) and SOUp are constant only the surface site mole fraction varies from one end-member to the next. As the site mole fraction shifts between the end-members, the fractional adsorption edges for the binary adsorbent mixtures varies between the limits defined by end-members. In the absence of particle-particle interactions, the adsorbents should act as independent ligands competing for complexa-tion of Cd(II). If this is the case, then the distribution of Cd(II) in such binary mixtures can be described by a composite mass-action expression (13) which includes a separate term for the interaction of Cd(II) with each adsorbent. 

Figure 14. Triple-layer model (1) results for Cd(II) adsorption onto a-alumina at different site/adsorbate ratios. Top, Cd(II) surface reaction best fit constants middle, Cd(II) surface species mole fractions and bottom, slopes of fractional adsorption edges used as the criteria of fit.

In the investigation of adsorbed species using XAS, it is not always possible to probe adsorbate—substrate bonding by changing to the adsorption edge of the adsorbate, for example, the adsorption of carbon monoxide on carbon supported Pt particles. Carbon... 

Fig.n.6 The effect of pH on the adsorption of some heavy metal cations on goethite and hematite, showing the typical adsorption edge for heavy metals (McKenzie, 1980, with permission). 

The alkaline earth ions have fairly diffuse adsorption edges which cover a wide pH range, e.g. 7-11.5 for (Ali and Dzombak, 1996) and 7-11 for Sr on... 

To date, only the second form of ternary adsorption has been observed for iron oxides. Davis and Leckie (1978 a) found that thiosulphate adsorbed on ferrihydrite in acid media with adsorption decreasing to zero as the pH rose to ca. 7, whereas the adsorption edge of silver lay between pH 7 and 8. In the presence of thiosulphate, adsorption of silver was enhanced in the pH range 4-6.5 (Fig. 10.10), i. e. 

The changes in local coordination of the majority specie (the substrate) at the surface (e.g. adsorbate induced reconstruction). It all depends on the detection mode and on the absolute surface sensitivity of the most surface sensitive detection mode. The way to proceed is to measure differential SEXAFS spectra on one adsorption edge of the substrate material, where the difference is made between the clean substrate and the exposed substrate, or between a bulk sensitive detection of the EXAFS, (TY, FY, high energy AEY) and a surface sensitive measure (low energy AEY). Attempts have been made on this groxmd, but final reports have not yet appeared in the literature. 

Figure 7.3 pH/solubility curves for anthropogeni-cally derived Zn, Pb and Cu in marine precipitation (Lim et al., 1994). In all cases a classical pH adsorption edge is seen indicating that pH dependent adsorption/desorption processes at the particle-water interface control the solubilities of these metals in rainwater. 

A wide range of chelate polymers with different metal ions has been studied as catalysts for H202 decompositions 49). Correlations were sought with the -adsorption edge as measured by X-ray spectroscopy. This property provides information about the electron distribution around the central metal atom and can give much information about its redox properties. The more recently developed technique of electron spectroscopy s°) can give much more accurate information of this kind and may prove to be a powerful tool in this respect. 

In our case, the measurements were done mainly at the colloid adsorption edge. In this region, for CdS it seems more correctly to approximate a(co) by a linear function... 

Figure 14.4 Metal binding on inorganic particles showing typical adsorption edges of selected anions and cations on Fe oxide particles reflective of metal-like and ligandlike complexes. (Modified from Santschi et al., 1997.)...

Figure 2. The adsorption edge parameters as a function of initial concentration of cadmium ions for metal oxide/electrolyte solution, containing cadmium, interface.

The adsorption curve of cadmium ions as a function of pH on metal oxide surfaces is characteristic for such systems, and is called the adsorption edge. The adsorption of cadmium increases with increasing pH, and is almost complete (-100%) at high pH. The adsorption edge shifts with an increase in the initial concentration of Cd2+ ions towards higher pH values. The adsorption of cadmium cations causes an increase of the t, potential, with an increase of total concentration of these ions in the system. 

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