Synthesis and Raman spectroscopic characterisation of hydrotalcite with CO₃²⁻ and VO₃⁻ anions in the interlayer

Infrared and Raman spectroscopy were used to characterise synthetic mixed carbonate and vanadate hydrotalcites of formula Mg 6 Al 2 (OH) 16 (CO 3 ) 2− , (VO 4 ) 3− ·4H 2 O. The spectra were used to assess the molecular assembly of the cations and anions in the hydrotalcite structure. The spectra may be conveniently subdivided into spectral features based on (1) the carbonate anion (2) the hydroxyl units and (3) water units. Bands were assigned to the hydroxyl stretching vibrations of water. Three types of carbonate anions were identified: (1) carbonate hydrogen‐bonded to water in the interlayer, (2) carbonate hydrogen‐bonded to the hydrotalcite hydroxyl surface and (3) free carbonate anions. It is proposed that the water is highly structured in the hydrotalcite, as it is hydrogen‐bonded to both the carbonate and the hydroxyl surface. The spectra were used to assess the contamination of carbonate in an open reacting vessel in the synthesis of vanadate hydrotalcites of formula Mg 6 Al 2 (OH) 16 (CO 3 ) 2− , (VO 4 ) 3− ·4H 2 O. Bands have been assigned to vanadate anions in the infrared and Raman spectra associated with VO bonds.