Preparation of Mg-Al layered double hydroxides intercalated with alkyl sulfates and investigation of their capacity to take up N,N-dimethylaniline from aqueous solutions

This study examined the effect of the interlayer spacing of a Mg-Al layered double hydroxide (Mg-Al LDH) on the ability of the Mg-Al LDH to take up a nonionic organic material. Mg-Al LDHs, intercalated with 1-propanesulfonate (PS^-), 1-hexanesulfonate (HS^-), and 1-dodecanesulfonate (DS^-), were prepared by coprecipitation, yielding PS·Mg-Al LDH, HS·Mg-Al LDH, and DS·Mg-Al LDH, respectively. The increase in the alkyl chain lengths of the Mg-Al LDHs (PS^- < HS^- < DS^-) resulted in the perpendicular orientation of the organic acid anions in the interlayer of Mg-Al LDH, which in turn resulted in more organic acid anions being accommodated in the interlayer space. An organic acid anion with a large molecular length was more easily intercalated in the interlayer of Mg-Al LDH than one with a small molecular length. This was attributed to the hydrophobic interaction between the alkyl chains, affecting the intercalation of the organic acid anions. The uptake of N,N-dimethylaniline (DMA) by Mg-Al LDHs increased in the order PS·Mg-Al LDH < HS·Mg-Al LDH < DS·Mg-Al LDH. The uptake was attributed to the hydrophobic interactions between DMA and the intercalated PS^-, HS^-, and DS^-. Thus, Mg-Al LDH, which has a lot of large interlayer spacings when intercalated with organic acid anions, can take up a large number of DMA molecules from an aqueous solution.