Hydrophobic layered double hydroxides (LDHs): Selective adsorbents for liquid mixtures

The external and internal surface area of the calcium aluminum double hydroxide [Ca2Al(OH)(6)] NO3.2H(2)O were hydrophobized by the anionic surfactants sodium dodecylsulfate and sodium dodecylbenzene sulfonate. The adsorption behavior towards liquid mixtures (benzene/n-heptane and n-propanol/toluene) was studied by determining the surface excess adsorption isotherms, the heats of immersion in these liquids, and the basal spacing, i.e. the expansion of the interlayer space. Both hydrophobic layered double hydroxides (LDHs) adsorbed n-heptane, benzene, toluene, and n-propanol between the layers with considerable increase of the basal spacing. Interlamellar swelling of the hydrophobizised LDHs in n-heptane was fundamentally different to the behavior of hydrophobized 2:1 clay minerals (smectites, vermiculites). The surface excess isotherms for benzene/heptane mixtures were U-shaped and indicate preferential adsorption of benzene. Dodecylbenzene sulfonate double hydroxide preferentially adsorbed propanol from n-propanol/toluene mixtures but the dodecylsulfate derivative adsorbed both compounds.