Structure and microstructure of nitrate layered Double Hydroxides

The structure and microstructure of nitrate Layered Double Hydroxides still represents a puzzle for the researchers in the field. In any given LDH family the unit cell of the nitrate member is unusually long: this suggests either that some extra space is present between anion and layers, or that the nitrate anion does not lay flat into the interlayer space. Moreover, it is not uncommon that the structure is not completely stable and that a portion of the nitrate anions are replaced by carbonates, due to the exposure of the specimens to the atmosphere. Transmission Electron Microscopy, X- ray powder diffraction, thermal analysis and 27Al ss MAS NMR spectroscopy have been employed to analyze this class of materials. The result is that the material is a complex interlayered system with the carbonate and nitrate anions occupying the interlayer space, the first laying flat, and the second partly inclined with respect to the stacking direction.