T. Rheinlander et al., ON THE ADSORPTION OF HYDROPHOBIC POLLUTANTS ON SURFACTANT CLAY COMPLEXES - COMPARISON OF THE INFLUENCE OF A CATIONIC AND A NONIONIC SURFACTANT/, Journal of dispersion science and technology, 19(2-3), 1998, pp. 379-398
The adsorption of the cationic surfactant dodecyl trimethyl ammonium b
romide (DTAB) and of the nonionic surfactant dodecyl octaethylene glyc
ol ether (C12E8) on four different layer silicates and their influence
on the sorption processes of the fungizide biphenyl were studied. Une
xpectedly, no great differences were found in comparing the adsorption
of the two surfactants on the basis of physicochemical investigations
, although the adsorption mechanism up to monolayer formation is funda
mentally different lion exchange and physisorption). Thus, the plateau
values of the adsorption isotherms and the molar enthalpies of displa
cement Delta(21)h are of the same order of magnitude for both surfacta
nts and the same basal spacing by intercalation is observed in the cas
e of swelling clays. The isotherms of the hydrophobic contaminant biph
enyl are of the linear C1-type at all layer silicates and very low ads
orption takes place approximately proportionally to the BET (N-2) surf
ace area. If the surface is weakly hydrophobized by surfactants (c(sur
factant)<<critical micelle concentration (CMC)), biphenyl adsorption i
s clearly increased. These processes can be adequately described using
the distribution coefficients K and K-OC (Henry coefficient related t
o the organic carbon content). K-OC is hardly influenced by the type o
f layer silicate for DTA(+)-layer silicates, whereas the C12E8 layer s
ilicate complexes generally show higher, but also different K-OC value
s. If the surfactant concentrations are above the CMC, solubilization
and adsorption compete for the pollutant molecules, which leads to a s
ignificant decrease in biphenyl adsorption.