Ligands, adsorption

The main mechanism of ligand adsorption is ligand exchange the surface hydroxyl is exchanged by another ligand. This surface complex formation is also competitive OH ions and other ligands compete for the Lewis acid of the central ion of the hydrous oxide (e.g., the Al(iii) or the Fe(III) in aluminum or ferric (hydr)oxides). The extent of surface complex formation (adsorption) is, as with metal ions, strongly... 

Figs. 2.8 and 2.9 exemplify the typical pH dependence for cation and ligand adsorption. As Fig. 2.9 illustrates the adsorption of the ligand A (or HA) goes through a maximum at a pH value that is near the pK value of HA. All kind of explanations have been given for the pH-dependence of this maximum it is important to realize that this maximum is a consequence of the mass law. 

Example 5.1 Change in Surface Protonation as a Consequence of Metal Ion or Ligand Adsorption... 

Figure 1. Adsorption of Cu ions on polymer ligand adsorption of Cu(II) on (O) QPVP O DBQP ( ) viscosity of QPVP solution in pH 5 CH,COOH-CHs-...

For all reactions, the mass transport regime is controlled by the diffusion of the reacting ligand only, as the mercury electrode serves as an inexhaustible source for mercury ions. Hence, with respect to the mathematical modeling, reactions (2.205) and (2.206) are identical. This also holds true for reactions (2.210) and (2.211). Furthermore, it is assumed that the electrode surface is covered by a sub-monomolecular film without interactions between the deposited particles. For reactions (2.207) and (2.209) the ligand adsorption obeys a linear adsorption isotherm. Assuming semi-infinite diffusion at a planar electrode, the general mathematical model is defined as follows ... 

Fig. 12.3 The three subsequent reaction steps of the dissolution of an Fe " oxide by an organic ligand ligand adsorption, iron detachment and proton adsorption (site restoration) (Stumm, Furrer, 1987, with permission).

That the reduction takes place at the surface, receives support from an experiment in which the extent of reduction of various Fe oxides by Shewanella alga after 30 days was linearly correlated with the SAbet the exception was 2-line ferrihydrite for which a surface area of 600 m /g had to be assumed in order to fit the relationship (Roden Zachara, 1996). Although experimental (BET) surface areas of ferrihydrite are substantially lower than 600 m /g, calculated values based on particle size as well as those determined from ligand adsorption experiments (see Table 5.1) are in this range. Dissolved Fe was found to create a lag phase in the reduction process (in contrast to the behaviour in inorganic systems) because Fe is adsorbed at the cell surface (Liu et al. 2001). This effect can be overcome by complexing the Fe (e. g. 

Figure 2. (a) Transition-metal adsorption by an immobilized ligand and (b) ligand adsorption by an immobilized transition-metal. 

To avoid the exchange of the immobilized transition-metal, for the transition-metal of the homogenous catalyst. Reverse Flow Adsorption requires two separate adsorption beds. The first bed for the recovery of the transition-metal center and the second bed for the ligand adsorption. 

The main mechanism of ligand adsorption is ligand exchange the surface hydroxyl is exchanged by another ligand. This surface complex formation is... 

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Ligand Adsorption Data Fitting Spectroscopic Evidence... 

The proposed mechanism for the ligand-promoted dissolution of aluminum oxide involves three general steps (1) ligand adsorption and surface complex formation, (2) slow detachment of a surface metal center (as a complex with the ligand), and (3) regeneration of the surface (shown schematically in Figure 1). 

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