Comprehending The Thermal Decomposition And Reconstruction Process Of Sol-Gel Mgal Layered Double Hydroxides

The evolution of MgAl layered double hydroxides (LDHs), prepared by the sol-gel method, throughout the synthesis-crystallization-calcination-reconstruction process is thoroughly studied and compared to a coprecipitated analogue. X-ray diffraction and transmission electron microscopy provide useful information about crystallinity and morphology of the samples. It was found that crystal sizes do not necessarily decrease after calcination-reconstruction. Furthermore, aluminum coordination is studied by (27)Al MAS nuclear magnetic resonance and by X-ray photoelectron spectroscopy (XPS), revealing significant differences in the relative populations of tetrahedral aluminum in the surface and the bulk of the calcined sol-gel LDHs. Magnesium and oxygen structural environments are also studied by XPS. A possible correlation between crystal sizes of calcined LDHs and the amount of O(2)(-) Surface species is discussed. Differences in the structural environment of magnesium in the as-synthesized and the reconstructed LDH are presented and analyzed.