Synthesis and properties of A6B2(OH)16Cl2·4H2O (A = Mg, Ni, Zn, Co, Mn and B = Al, Fe) materials for environmental applications

Double layered hydroxide materials of composition A₆B₂(OH)₁₆Cl₂·4H₂O (A = Mg, Ni, Zn, Co, Mn and B = Al, Fe) were synthesized by chemical precipitation at 60 °C. Different levels of crystallinity and ordering degree were observed depending upon the chemical environment or the combination between divalent and trivalent cations. The results from high-resolution transmission electron microscopy revealed that nanostructured layered samples were obtained with interplanar spacing compatible with previous literature. Raman scattering was employed to investigate the complex band structure observed, particularly the lattice vibrations at lower frequencies, which is intimately correlated to the cationic radius of both divalent and trivalent ions. The results showed that strongly coordinated water and chloride ions besides highly structured hydroxide layers have a direct influence on the stability of the hydrotalcites. It was observed that transition and decomposition temperatures varied largely for different chemical compositions.