Changes in the SiO stretching bands are also observed upon thermal treatment and its is suggested that as the pillar is locked into the structure, a reaction between the alumina pillar and the siloxane surface occurs. Thus IES technique allows the identification of new inorganic materials and the changes in the molecular structure of these materials as thermal transformations occur. Hydrotalcites often known as LDH's or double-layered hydroxides are anionic clays found in nature but more often synthesised as precursors for catalysts. The difference between the normal clay minerals and the hydrotalcites is that the clay layer surface charge is positive and consequently this layer charge is counterbalanced by anions such as carbonates or nitrate ions. A demarks the hydroxyl stretching region and changes in this region as thermal transformation occurs.
B shows the presence of organics in the spectra.
C shows the presence of the interlayer carbonate in the structure. D demarks the AlO bands. The bands observed at near 2100 cm -1 is probably the overtone of this band. Clearly the spectra show the changes in the molecular structure of the hydrotalcite as it is transformed into a Ni spinel and NiO. Figure 5. Infrared emission spectra of Ni-hydrotalcite in the temperature range 200 to 750 C at 50 C intervals.