Raman spectroscopy of gallium‐ and zinc‐based hydrotalcites

Insight into the unique structure of hydrotalcites (HTs) has been obtained using Raman spectroscopy. Gallium‐containing HTs of formula Zn 4 Ga 2 (CO 3 )(OH) 12 · x H 2 O (2:1 ZnGa‐HT), Zn 6 Ga 2 (CO 3 )(OH) 16 · x H 2 O (3:1 ZnGa‐HT) and Zn 8 Ga 2 (CO 3 )(OH) 18 · x H 2 O (4:1 ZnGa‐HT) have been successfully synthesised and characterised by X‐ray diffraction (XRD) and Raman spectroscopy. The d (003) spacing varies from 7.62 Å for the 2:1 ZnGa‐HT to 7.64 Å for the 3:1 ZnGa‐HT. The 4:1 ZnGa‐HT showed a decrease in the d (003) spacing, compared to the 2:1 and 3:1 compounds. Raman spectroscopy complemented with selected infrared data has been used to characterise the synthesised gallium‐containing HTs. Raman bands observed at around 1050, 1060 and 1067 cm −1 are attributed to the symmetric stretching modes of the (CO 3 2− ) units. Multiple ν 3 (CO 3 2− ) antisymmetric stretching modes are found between 1350 and 1520 cm −1 , confirming multiple carbonate species in the HT structure. The splitting of this mode indicates that the carbonate anion is in a perturbed state. Raman bands observed at 710 and 717 cm −1 and assigned to the ν 4 (CO 3 2− ) modes support the concept of multiple carbonate species in the interlayer.