Structured water in hydrotalcites of formula MgxZn6−xAl2(OH)16(CO3)·4H2O: a Raman microscopic study

Abstract Raman microscopy was used to characterize synthesized hydrotalcites of formula MgxZn6−xAl2(OH)16 (CO3)·4H2O. The Raman spectra are conveniently subdivided into spectral features based on (a) the carbonate anion, (b) the hydroxyl units and (c) metal–oxygen units. A model is proposed based on a tripod of M3OH units in the hydrotalcite structure. In a simplified model, Raman spectra of the hydroxyl‐stretching region enable bands to be assigned to the Mg3OH, Zn3OH and Al3OH units. Bands are also assigned to the hydroxyl stretching vibrations of water. Three types of water are identified: (a) water hydrogen bonded to the interlayer carbonate ion, (b) water hydrogen bonded to the hydrotalcite hydroxyl surface and (c) interlamellar water. A model of water in the hydrotalcite structure is proposed in which water is in a highly ordered structure as it is hydrogen bonded to both the carbonate anion and the hydroxyl surface and also forms bridges between the MOH surface and the carbonate anion. Copyright © 2002 John Wiley & Sons, Ltd.