On the adsorption of hydrophobic pollutants on surfactant/clay complexes: Comparison of the influence of a cationic and a nonionic surfactant

摘要

The adsorption of the cationic surfactant dodecyl trimethyl ammonium bromide (DTAB) and of the nonionic surfactant dodecyl octaethylene glycol ether (C12E8) on four different layer silicates and their influence on the sorption processes of the fungizide biphenyl were studied. Unexpectedly, 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 fundamentally different lion exchange and physisorption). Thus, the plateau values of the adsorption isotherms and the molar enthalpies of displacement Delta(21)h are of the same order of magnitude for both surfactants and the same basal spacing by intercalation is observed in the case of swelling clays. The isotherms of the hydrophobic contaminant biphenyl are of the linear C1-type at all layer silicates and very low adsorption takes place approximately proportionally to the BET (N-2) surface area. If the surface is weakly hydrophobized by surfactants (c(surfactant)critical micelle concentration (CMC)), biphenyl adsorption is clearly increased. These processes can be adequately described using the distribution coefficients K and K-OC (Henry coefficient related to the organic carbon content). K-OC is hardly influenced by the type of layer silicate for DTA(+)-layer silicates, whereas the C12E8 layer silicate complexes generally show higher, but also different K-OC values. If the surfactant concentrations are above the CMC, solubilization and adsorption compete for the pollutant molecules, which leads to a significant decrease in biphenyl adsorption. [References: 32]