The application of near-infrared spectroscopy to the study of brucite and hydrotalcite structure

Brucite and hydrotalcite molecular structures have been studied using near- IR reflectance spectroscopy. Three Near-IR spectral regions are identified: (a) the high frequency region between 6400 and 7400 cm(-1) attributed to t he first overtone of the fundamental hydroxyl stretching mode, (b) the 4800 -5400 cm(-1) region attributed to water combination modes of the hydroxyl f undamentals of water, and (c) the 4000-4800 cm(-1) region attributed to the combination of the stretching and deformation modes of the MOH units of hy drotalcite. Brucites are characterized by intense bands at 7154 and 4298 cm (-1). NIR spectroscopy enables the separation of the hydroxyl bands of the water and M-OH units for the hydrotalcites. Compared with the NIR spectrosc opy of the structural units of the hydrotalcites namely gibbsite and brucit e, the bands are broad. Five bands are identified in the hydroxyl stretchin g overtone region centred around 7650, 7215 7078, 6918 and 6600 cm(-1). Wat er combination bands were found at similar to 5200, 5130 4980 and 4800 cm(- 1). Two types of water were identified: water coordinated to the hydroxyl s urface and water coordinated to the interlayer anion. Combination bands of the hydroxyl fundamentals were identified at similar to 4430 4295 4090 and 4010 cm(-1).