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. Industrial Applications Infrared emission spectroscopy has the potential for wide applications in industry, such as in process control and quality assurance. Providing the sample is at some elevated temperature compared to the detector temperature then a spectrum of the sample may be obtained.