Synthesis and characterization of laurate-intercalated Mg–Al layered double hydroxide prepared by coprecipitation

Effective utilization of layered double hydroxides (LDH) for industrial applications requires the synthesis of pure and well-defined LDH phases. In the present study, dodecanoate (laurate) anions were intercalated into Mg–Al-layered double hydroxide (LDH-C₁₂) by coprecipitation in the presence of an aqueous ethanolic laurate solution at a constant pH of 9 and room temperature. The effect of varying the Mg:Al molar ratio (2:1 or 3:1), the Al:laurate molar ratio, and ethanol concentration (0, 30 or 40% v/v ) was investigated. A pure LDH-C₁₂ phase was obtained using a Mg:Al molar ratio of 2:1, a Al:laurate molar ratio of 1:1 and 30% v/v ethanol, and a post-synthesis hydrothermal treatment at 75°C for 12h. An additional impurity phase formed in syntheses having a Mg:Al molar ratio at 3:1 and/or in the presence of excess laurate anions. This phase has previously been misinterpreted as a particular LDH-C₁₂ intercalated structure, but we here demonstrate it to be magnesium laurate (Mg-C₁₂). The LDH-C₁₂ compound showed high structural order with a basal spacing of 2.41nm. Fourier-transform IR-spectra confirmed the intercalation of the laurate anions in the interlayer. Transmission electron microscopy showed plate-like, irregularly shaped crystals with lateral dimensions in the range of 100–200nm and plate thickness smaller than 40nm. Scanning electron microscopy revealed nonporous aggregates of LDH-C₁₂.