Synthesis And Raman Spectroscopic Characterisation of Hydrotalcite with CO32- and VO3- Anions In The Interlayer

Infrared and Raman spectroscopy have been used to characterise synthetic mixed carbonate and vanadate hydrotalcites of formula Mg6Al2(OH)16(CO3)2-,(VO4)3-.4H2O. The spectra have been 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 (a) upon the carbonate anion (b) the hydroxyl units (c) water units. Bands are assigned to the hydroxyl stretching vibrations of water. Three types of carbonate anions are identified (a) carbonate hydrogen bonded to water in the interlayer (b) carbonate hydrogen bonded to the hydrotalcite hydroxyl surface and (c) 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 have been used to assess the contamination of carbonate in an open reacting vessel in the synthesis of a vanadate hydrotalcites of formula Mg6Al2(OH)16(CO3)2-,(VO4)3-.4H2O. Bands have been assigned to vanadate anions in the infrared and Raman spectra associated with V-O bonds.