Near-infrared spectroscopy of stitchtite, iowaite, desautelsite and arsenate exchanged takovite and hydrotalcite

Three Near-IR spectral regions are identified: (a) the high wavenumber region between 6400 and 7400 cm−1 attributed to the first overtone of the fundamental hydroxyl stretching mode, (b) the 4800-5400 cm−1 region attributed to water combination modes of the hydroxyl fundamentals 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 the hydrotalcites. NIR spectroscopy enables the separation of the hydroxyl bands of the water and M-OH units for the hydrotalcites. Compared with the NIR spectroscopy of the structural units of the hydrotalcites namely gibbsite and brucite, the bands are broad.