Silicate surface layer

MCBRIDE Paramagnetic Probes of Layer Silicate Surfaces... 

Figure 8. Several orientations of TEMPAMINE at the layer silicate surface with a. maximum CHj-surface interaction (0 45°), b. minimum CHj-surface interaction (0 > 45°), c. minimum mobility (0 M)°). 0 is defined in Figure 7.

McBride, M. B. (1986). Paramagnetic probes of layer silicate surfaces. In Geochemical Processes at Mineral Surfaces, Davis, J. A, and Hayes, K. F., eds., American Chemical Society Washington, D.C., pp. 362-388. 

Correlation between the organic matter ionically bound to the layered silicate surface and the resulting basal plane spacing of the modified filler. (Reproduced from Mittal, V., /. Thermoplast Compos. Mater., 20, 575,2007.)... 

Layered silicates, surface modifications, and thermal stability... 

In principle, the adsorption of organic environmental chemicals on layer silicates proceeds extremely slowly so that it may take several weeks to establish an equilibrium state [22]. In contrast, if the layer silicate surface is coated with cationic surfactants in different quantities [22] or of different hydrophobicity, e.g., with DTAB (dodecyl trimethyl ammonium bromide) or DDDMAB (didoceyl dimethyl ammonium bromide) [23] then equilibrium in both systems is reached within 30 min, i.e., a drastic increase in the adsorption rate of organic pollutants results. Their residence time or probability of residence in the soil electrolyte is therefore drastically reduced and their bioavailability thus also drops. 

Apart from the cationic surfactants, non-inonic surfactants also cause an increased hydrophobization of the layer silicate surface with increasing concentration, thus promoting, for example, the adsorption of the hydro-phobic fungicide biphenyl (see Fig. 16) [26]. The increased biphenyl adsorption also measured at a very weakly hydrophobized bentonite (10 pmol non-ionic surfactant/g bentonite) indicates that these effects also become active even with very small (environmentally relevant) surfactant concentrations. 

In the case of clay minerals pretreated with small amounts of anionic surfactants (e.g., sodimn dodecylsulphate (SDS), c < CMC (critical micelle concentration)), for example, the adsorption of biphenyl is not significantly influenced in comparison to pure layer silicates [26]. These findings may be explained, among other aspects, by the low adsorption potential for anionic surfactants of the negatively charged layer silicate surface (cf. Fig. 17, curve A). Quite different conditions exist in acid soils, in which the soil minerals may be positively charged. As... 

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