Sol-gel synthesis of hydrotalcite — like compounds

Sol-gel hydrotalcite-like compounds were prepared using two different magnesium precursors, on the one hand magnesium ethoxide and on the other magnesium acetylacetonate. The aluminum precursor was always aluminum acetylacetonate. The resulting interlayer anions were ethoxide–acetylacetonate and acetylacetonate, respectively. Instead of the conventionally accepted thermal autoclave treatment, a new gelling and crystallization method is proposed using microwave irradiation. The solids were characterized by X-ray diffraction, nitrogen physisorption, thermogravimetric analysis, infrared spectroscopy and transmission electron microscopy. It is found that the acetylacetonate precursors determine surface area and crystallinity. Microwave irradiation guarantees a high surface area for an irradiation time as low as 10 min. C 2006 Springer Science + Business Media, Inc. 1. Introduction Hydrotalcite-like compounds, also referred as double layered hydroxides, are anionic clays. The layer structure is determined by divalent cations octahedrally coordinated to the surrounding hydroxide ions. Some of them may be isomorphously replaced by three-valent atoms which produce positively charged layerswhose charge is neutralized by SO4 2−, Cl− or NO3− anions among others [1–4]. The most common hydrotalcite-like compound, known as hydrotalcite, is constituted by magnesium and aluminum. In this material, the positive charges are compensated by CO3 2− solvated anions. Hydrotalcite conventional synthesis method has been significantly improved substituting the conventional hydrothermal treatment step by microwave irradiation [5– 7]. The autoclave high temperature treatment is, in this way, avoided and the long crystallization time is substantially reduced. However, the crystallite size of the obtained ∗Author