Nanohybrid materials from the intercalation of imidazolium ionic liquids in kaolinite

A series of novel organic - inorganic nanohybrid materials were obtained by the intercalation in the interlamellar spaces of the clay mineral kaolinite, of ionic liquids based on imidazolium derivatives. The intercalation procedure was successfully accomplished via a melt reaction strategy using the dimethylsulfoxide - kaolinite intercalate (DMSO-K) as a precursor. C-13 MAS NMR as well as XRD, TGA/DTA and FTIR studies confirmed the complete displacement of DMSO molecules by the imidazolium salts during the intercalation process. Increase of the basal spacing from 1.1 nm in DMSO-K to 1.3 - 1.7 nm in the nanohybrid materials was observed, indicating that imidazolium derivatives are oriented in a way such that the imidazole ring is parallel, or slightly tilted by an angle of 10 - 25 degrees, with respect to the kaolinite internal surfaces. The number of moles of organic material loaded in the nanohybrids was obtained from several independent measurements. The intercalation of the imidazolium salts increases the thermal stability of the resulting material by more than 150 degrees C with respect to DMSO-K. After heating under air at 300 degrees C for two hours, XRD showed that the structure of the intercalates was kept with only a slight decrease of the intercalation ratio. The original kaolinite structure was recovered after heating the intercalate at 350 degrees C for an additional two hours. This observed high thermal stability is promising for the use of these nanohybrid materials as precursor for the synthesis of new nanocomposites by incorporation of polymer in kaolinite at high temperature.