FT-Raman and FT-IR Spectroscopic Study of Synthetic Mg/Zn/A1-Hydrotalcites

Synthetic Mg/Zn/Al-hydrotalcites with atomic ratios of 6:0:2, 4:2:2, 2:4:2 and 0:6:2 were characterized by FT-Raman and FT-IR spectroscopy. ‘Al--OH’ IR translation modes are observed at 419, 427, 559, 616 and 771 cm⁻¹ with two corresponding Raman bands at 465–477 and 547–553 cm⁻¹. ‘Mg--OH’ IR translation modes are found at 412, 559 and 616 cm⁻¹ with equivalent Raman bands at 464–477 and 547–553 cm⁻¹. The ‘Zn--OH’ IR translation mode is found at 445 cm⁻¹ and the Raman modes around 450 and 495 cm⁻¹. The CO₃^{2 −} group is identified by the ν₁(IR) at 1112 cm⁻¹ and a doublet in the Raman around 1045–1055 and 1060 cm⁻¹. ν₂(IR) is observed at 874 cm⁻¹. ν₃(IR) is a doublet at 1359 and 1381 cm⁻¹. ν₄ is observed in both the IR and Raman spectra around 670 and 695–715 cm⁻¹, respectively. In the OH deformation region, a doublet is observed for ‘Al--OH’ at 955 and 1033 cm⁻¹ in the IR spectra. The ‘Zn--OH’ IR deformation mode is observed at 1462 cm⁻¹. H₂O is characterized by a bending mode at 1632 cm⁻¹ and an H-bonded interlayer H₂O mode at 3266 cm⁻¹ with a Raman band between 3244 and 3271 cm⁻¹. The OH stretching region is characterized by three bands in the Raman spectra around 3355–3360, 3440–3455 and 3535–3580 cm⁻¹. One band is observed in the IR spectra at 3471 cm⁻¹.