Abstract
Layered double hydroxides (LDHs) containing Mg 2+, Al 3+ and Ti 4+ with varying molar ratios of Al 3+/Ti 4+ were prepared by co-precipitation at constant pH. Characterisation of the samples as synthesised and their calcined products by bulk chemical analyses, powder XRD, TG-DTA, FT-IR and diffuse reflectance spectroscopy, N 2 physisorption and TPD of CO 2 indicated well crystalline hydrotalcite like structures with Ti 4+ in the brucite layer. The introduction of Ti 4+ in the layer induced a distortion of the brucite like sheet which results in LDH precursors with decreased crystallinity. Calcination at 450 °C gave rise to mixed oxides with poorly crystalline MgO type structures, which can be reconstructed to their original structure by exposure to an aqueous solution. Both, the surface area and the number of basic sites of calcined samples decreased with increase of the Ti 4+ content in the samples. Substitution of Ti 4+, either for Mg 2+ or Al 3+, increased the adsorption capacity of the calcined samples up to 20%, thus providing indirect evidence in favour of Ti 4+ in the brucite layer.
Published Version
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