Abstract
Intercalation behavior of anionic surfactants such as dodecyl sulfate ion (DS-), dodecylbenzene sulfonate ion (DBS-) and octyl sulfonate ion (OS-) was researched using Mg/Al type layered double hydroxide (LDH) with anion exchange ability. The effect of ion size and amount of surfactant adsorbed on the interlayer distance of LDH was investigated. In order to apply the LDH modified with the surfactants to the adsorption of organic compounds in aqueous solution, adsorption tests were carried out for six kinds of organic compounds.
Adsorption isotherms of DS-, DBS- and OS- with the LDH were of the Langmuir type. Saturated adsorption amounts calculated by the Langmuir analysis were in the order, DBS-> DS-> OS-. In the case of DBS-, the saturated adsorption amount was almost equal to the theoretical exchange capacity of LDH (341 meq/100 g), whereas the adsorption equilibrium constant was in the order, DS-> DBS-> OS-. The surfactants in the LDH interlayer were horizontally orientated in the direction of the LDH basal seat in the region of lower adsorption, becoming vertically orientated with an increase in amount of surfactant adsorbed. The amount of surfactant adsorbed in the transition region was found to vary with the kind of surfactant. The order of toluene removal with the surfactant-modified LDH was as follows; DBS-> DS-> OS-. In the case of DS--modified LDH, the adsorption isotherms for various organic compounds were classified as Henry type, and their slopes corresponded to the octanol-water distribution coefficient, which indicates the degree of hydrophobicity of organic compounds.
