Study of synthesis and optical properties of transition metal substituted LDH nanoparticles

Mg3-x-yM×M'y/Al1 is the general formula of double metal-substituted magnesium aluminum layered double hydroxides. In this study, Mg-Al LDH, where magnesium is substituted by two different metal cations, M (Zn) and M' (Ni or Co), in the brucite-like layers of the LDH. MgZnNiAl LDH and MgZnCoAl LDH were successfully synthesized through the sol-gel method under optimized conditions. The corresponding LDH materials were prepared with different stoichiometry by varying the molar ratios of Mg:Ni and Mg:Co whereas zinc and aluminum concentrations were kept constant. The as-prepared LDH materials were thoroughly investigated by a range of analytical techniques such as FT-IR spectroscopy, X-ray diffraction and also ultraviolet-visible spectroscopy, which provided a wide understanding of the compositional and structural characteristics of the Mg-Al LDH. The obtained data of UV-Vis spectroscopy and XRD were utilized to calculate lattice parameters (a and c), crystallite sizes (D), microstrain (ε), positions and displacements of atoms (u), volume of the unit cell (v), band gap, and dielectric constant. XRD data revealed similar patterns for the MgZnNiAl LDH and MgZnCoAl LDH, suggesting that they have common structural backbone, moreover, MgZnNiAl LDH samples showed a higher crystallinity. FT-IR spectra showed the distinct bands corresponding to the vibrational modes of the hydroxyl groups (OH-) and nitrate (NO3-) groups within LDH structure. Moreover, it was found that varying concentrations of metal cations significantly affected the composition, structure, optical properties and functional characteristics of LDH materials.