Structural characterization of chlorine intercalated Mg-Al layered double hydroxides: A comparative study between mechanochemistry and hydrothermal methods

Abstract

The chlorine intercalated Mg-Al layered double hydroxides (Mg-Al-Cl-LDH) with chemical formula of Mg1−XAlX(OH)2 Cl−X were successfully prepared by the one step mechanochemical activation and hydrothermal methods. For a comparative study of the mechanically activated samples versus hydrothermally treated specimens, the structural features such as crystallite size, lattice strain, crystallinity, the interlayer spacing, and the unit cell volume of samples were examined. Results revealed that the phase purity of products was strongly influenced by different ion substitution degrees (X = 0.12, 0.18, 0.3, and 0.42). From X-ray diffraction (XRD) analysis, Brucite and Hydrotalcite were dominant phases at low ions substitution (X), while Gibbsite and Hydrotalcite were main peaks at high ions substitution (X) for both methods. Pure Hydrotalcite was obtained in the midrange. The unit cell volume and interlayer spacing of LDH obtained from both processes was also strongly influenced by degrees of substitutions so that it shows a downward trend as ion content increased. FESEM and TEM observations revealed that that the LDH powders possesses a typical platelet-like microstructure, so that the average crystallite size of hydrothermal samples was greater than milled samples. Detailed analysis of the phase behavior and structural trends revealed that Mg-Al-Cl-LDH can be synthesized much more easily and rapidly in high energy ball mill as compared with an analogous LDH prepared by hydrothermal method. However, the product obtained from hydrothermal method showed the greater crystallinity.