Modification of the hydroxyl surface of kaolinite through mechanochemical treatment followed by intercalation with potassium acetate

Changes in the hydroxyl surfaces of kaolinite have been studied through mechanochemical activation followed by intercalation with potassium acetate using a combination of X-ray diffraction and diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy. X-ray diffraction shows that in the absence of air the intercalated kaolinite is expanded to 11.9 Angstrom with an additional expanded phase at 9.07 Angstrom. The degree of expansion is related to the orientation of the acetate between the kaolinite layers. Upon exposure to moist air; the kaolinite re-expands to 14.2 and 10.02 Angstrom. Upon mechanochemical activation of the kaolinite for 1 h and intercalation with potassium acetate, a phase with a d spacing of 8.80 Angstrom is obtained which upon exposure to moist air re-expands to 13.50 Angstrom. Changes in the molecular structure of the mechanochemically activated intercalated kaolinite were followed by DRIFT spectroscopy. Fundamentally the intensity of the kaolinite hydroxyl stretching bands decreased exponentially with grinding time, and concomitantly the intensity of the bands attributed to the OH stretching vibrations of water increased. It is proposed that the mechanochemical activation of the kaolinite caused the conversion of the hydroxyls to water which coordinates the kaolinite surface. Significant changes in the infrared bands assigned to the hydroxyl deformation and translation modes were observed. The intensity decrease of the bands was linearly related to the grinding time.