Surfactant-assisted fatty acid intercalation of layered double hydroxides

Surfactant-mediated intercalation of aliphatic carboxylic acids into a commercial layered double hydroxide (LDH) with approximate composition Mg0.689Al0.311(OH)(2)](CO3)(0.156)center dot 0.5H(2)O] was explored. The reaction was conducted at elevated temperatures with the LDH powder as a suspension in a stearic acid oil-in-water emulsion. The acidic fatty acid, e. g., stearic acid, reacts with the basic carbonate anions, CO2 is released and the fatty acid is intercalated as a bilayer. High-concentration anionic or nonionic surfactants, i.e., sodium dodecylsulfate or Tween 60, aid the intercalation process by emulsifying the molten acid and dispersing the hydrotalcite particles. X-ray diffraction, thermal analysis, and infrared spectroscopy confirmed that a bilayer-intercalated hydrotalcite was formed and that the surfactant is not co-intercalated. The method is convenient, economical, and environmentally friendly: It employs the readily available carbonate form as starting reagent; water is used as medium rather than organic solvents; low reaction temperatures suffice, i.e., calcinations of the clay are superfluous and there is no need for working under a CO2-free atmosphere.