Synthesis and adsorption properties of p-sulfonated calix[4 and 6]arene-intercalated layered double hydroxides

The intercalation of water-soluble p-sulfonated calix[4 and 6]arene (CS4 and CS6) in the interlayer of the Mg–Al and Zn–Al layered double hydroxide (LDH) by the coprecipitation method has been investigated, as well as the adsorption properties of the resulting CS/LDHs for benzyl alcohol (BA) and p-nitrophenol (NP) to prepare new microporous organic–inorganic hybrid adsorbents. The amount and arrangement of CS intercalated was different by the kind of the host metal ions. CS4 cavity axis was perpendicular for the Mg–Al LDH basal layer and parallel for the Zn–Al LDH basal layer, while CS6 cavity axis was perpendicular for both the LDH basal layers. In the BET surface area measurement, the surface area of the Zn–Al/CS4/LDH was four times than that of the Mg–Al/CS4/LDH, expecting that the former has higher adsorption capacity than the latter. In fact, the adsorption ability of the CS/LDHs for BA and NP in aqueous solution was found to be larger in the Zn–Al/CS4/LDH than in the Mg–Al/CS4/LDH. In addition, the adsorption ability of both the LDHs was larger in the CS6/LDHs than in the CS4/LDHs. These results were explained by the difference in the amount and arrangement of CS intercalated in the LDH interlayer space.