Textural properties of layered double hydroxides: effect of magnesium substitution by copper or iron

Layered double hydroxides (LDHs), in which magnesium was partially substituted by iron or copper, were synthesized by a coprecipitation method. The materials were characterized by X-ray diffraction, X-ray fluorescence, FT-IR spectroscopy, N-2 adsorption, scanning electron microscopy and transmission electron microscopy. The treatment of the adsorption-desorption isotherms with different computation models permitted the determination of several parameters, useful for thorough characterization of the microstructures of the samples. The substituted samples preserved the hydrotalcite-type layered structure though their textural properties underwent important modifications. For copper substituted LDH, a relatively uniform porous structure with emphasized mesoporous characteristics emerged, the mesopores were enlarged and the specific surface area was decreased. On the contrary, for iron substituted LDH, the microporosity features developed, nonuniformity and constrictions in the porous structure was accentuated, the pore size was decreased and the specific surface area was increased. Microscopic morphology characteristics contributed to establish the textural properties of the samples. (C) 2001 Elsevier Science B.V. All rights reserved.