Thermally induced grafting reactions of ethylene glycol and glycerol intercalates of kaolinite

Inorganic-organic layered hybrid materials based on kaolinite were prepared from dehydrated potassium acetate intercalated through the guest-displacement reaction with ethylene glycol and glycerol. These materials were characterized and their behavior upon heating was investigated using X-ray diffraction, diffuse reflectance Fourier transform infrared spectroscopy, and combined thermogravimetry and differential scanning calorimetry coupled with mass spectroscopy. An intense perturbation of the AlAlOH stretching vibrations of kaolinite in the range 3700-3600 cm(-1) was observed for both of the intercalates, indicating strong interactions with the kaolinite surface OH groups. The two intercalates showed different thermal behavior. The ethylene glycol intercalates decomposed in a nitrogen atmosphere at 160 degrees C, with the release of the ethylene glycol from adjacent kaolinite layers. The glycerol intercalate showed a three-step decomposition over the temperature range 115-465 degrees C associated with dehydroxylation reactions, and a further decomposition reaction at 486 degrees C. The final reaction was due to the decomposition of the glycerol molecules grafted on the kaolinite surface and could be followed by monitoring the ion current in the mass spectrometer for masses corresponding to H2O+, C2H4O+ and/or CO2+, and O+ and/or CH4+ molecular fragments, typical of the decomposition products of oxygen-bearing organic matter. Combined thermogravimetry-mass spectrometry proved to be an extremely useful tool for studying the thermal behavior of inorganic-organic layered hybrid materials.