Raman spectroscopy of some natural hydrotalcites with sulphate and carbonate in the interlayer

The structures of a series of nickel- and magnesium-based hydrotalcites were explored using Raman microscopy. These natural hydrotalcites are based upon sulphate or carbonate being the counter anion in the interlayer. Variation in the position of the sulphate stretching vibrations occurs and is mineral dependent. Raman spectroscopy shows a reduction in the symmetry of both sulphate and carbonate, which leads to the conclusion that the anions are bonded to the brucite-like hydroxyl surface and to the water in the interlayer. Water bending modes are identified in both the Raman and infrared spectra at positions greater than 1630 cm, indicating that the water is strongly hydrogen bonded to both the interlayer anions and the hydrotalcite surface