Structure of surfactant-clay complexes and their sorptive characteristics toward HOCs

摘要

The influence of structural characteristics of series of surfactant-day complexes on their sorption capacities toward naphthalene were examined, which presented some novel information about how to improve the sorption capacities of the complexes. It was shown that sorption of naphthalene on these complexes strongly depended on the conformations of the adsorbed surfactants, and the organic carbon normalized sorption coefficient (K_(oc)) value varied in a wide range (5000-20,000 L/kg) with surfactant conformation. That was, K_(oc) value first increased gradually until the maximum and then decreased sharply as the surfactant conformation developed progressively from liquidlike to solidlike (i.e., increasing surfactant packing density and ordering). At low packing density stage the surfactant aggregates have high surface/volume ratio and the attractive forces between surfactant and solute are relatively weak; whereas at high packing density stage interactions between surfactant alkyl chains are strong and more free energy is needed for creating cavities in the surfactant mediums. In both cases the sorption capacities of the complexes are weak. Thereby, the surfactant aggregates can be considered as different partition phases as their conformations changed, which then lead to the variation of K_(oc) value. Controlling the surfactant aggregates within intermediate packing density range can optimize the sorption capacities of the complexes.