Cu-Al layered double hydroxides intercalated with 1-naphthol-3,8-disulfonate and dodecyl sulfate: Adsorption of substituted phenols from aqueous media

Cu-Al layered double hydroxides (Cu-Al LDHs) intercalated with 1-naphthol-3,8-disulfonate (1-N-3,8-DS^2-) and dodecyl sulfate (DS^-) were prepared by coprecipitation. Based on X-ray diffraction patterns, 1-N-3,8-DS^2- and DS^- are most probably oriented perpendicularly to the brucite-like Cu-Al LDH layers. The 1-N-3,8-DS·Cu-Al LDH was able to adsorb substituted phenols from aqueous solution, with the degree of uptake decreasing in the following order: 3-nitrophenol (N-phe) > 3,5-dichlorophenol (DCl-phe) > 4-chlorophenol (Cl-phe) > 2-methoxy-4-methylphenol (MM-phe) ≈ 4-methoxyphenol (Me-phe). The preferential uptake of the substituted phenols by 1-N-3,8-DS·Cu-Al LDH is attributed to π-π stacking interactions between the phenolic aromatic ring and the naphthalene core of the intercalated 1-N-3,8-DS^2-. The DS·Cu-Al LDH also adsorbed substituted phenols from aqueous solution, albeit randomly. This random uptake is attributed to hydrophobic interactions between the alkyl groups of the DS^- intercalated in the interlayer and the aromatic rings of the aqueous adsorbates.