Organic molecules, surface concentration

The effects of organic molecules and phosphate on the adsorption of acid phosphatase on various minerals, and kaolinite in particular, have been investigated by Huang et al. [97]. The Langmuir affinity constant for AcP adsorption by kaolinite follows the series tartrate (K — 97.8) > phosphate (K= 48.6) > oxalate (K — 35.6) > acetate (K= 13.4). At low concentration, acetate even promoted the adsorption of acid phosphatase. It was considered that competitive interactions between anionic adsorbates can occur directly through competition for surface sites and indirectly through effects of anion adsorption on the surface charge and protonation. 

The processes classified in the third group are of primary importance in elucidating the significance of electric variables in electrosorption and in the double layer structure at solid electrodes. These processes encompass interactions of ionic components of supporting electrolytes with electrode surfaces and adsorption of some organic molecules such as saturated carboxylic acids and their derivatives (except for formic acid). The species that are concerned here are weakly adsorbed on platinum and rhodium electrodes and their heat of adsorption is well below 20 kcal/mole (25). Due to the reversibility and significant mobility of such weakly adsorbed ions or molecules, the application of the i n situ methods for the surface concentration measurements is more appropriate than that of the vacuum... 

Let us consider the uptake of a given species, either a nutrient or a pollutant heavy metal or an organic (macro)molecule, etc., which will be referred to as M. M is present in the bulk of the medium at a concentration, c, ar d we assume that the only relevant mode of transport from the medium to the organism s surface is diffusion. The internalisation sites are taken to be located on the spherical surface of the microorganism or in a semi-spherical surface of a specialised region of the organism with radius ro (see Figure 1). Thus, diffusion prescribes ... 

A change in ionic adsorption in the presence of organic molecules was also observed by Parsons and Zobel. They found that in the presence of acetanilide in the inner layer, the surface concentration of specifically adsorbed phosphate ions decreases. In another work it was suggested that specific adsorption of nitrate ions is markedly reduced in the presence of thiourea in the solution. Thiourea alters the properties of the mercury electrode, affecting even the adsorption of iodides. ... 

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