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 an d n-propanol/toluene) was studied by determining the surface excess ad sorption isotherms, the heats of immersion in these liquids, and the b asal spacing, i.e. the expansion of the interlayer space. Both hydroph obic layered double hydroxides (LDHs) adsorbed n-heptane, benzene, tol uene, 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 hydrophobi zed 2:1 clay minerals (smectites, vermiculites). The surface excess is otherms for benzene/heptane mixtures were U-shaped and indicate prefer ential adsorption of benzene. Dodecylbenzene sulfonate double hydroxid e preferentially adsorbed propanol from n-propanol/toluene mixtures bu t the dodecylsulfate derivative adsorbed both compounds.