Synthesis, characterisation and rehydration behaviour of titanium(IV) containing hydrotalcite like compounds

Abstract

Layered double hydroxides (LDHs) containing Mg2+, Al3+ and Ti4+ with varying molar ratios of Al3+/Ti4+ 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, N2 physisorption and TPD of CO2 indicated well crystalline hydrotalcite like structures with Ti4+ in the brucite layer. The introduction of Ti4+ 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 Ti4+ content in the samples. Substitution of Ti4+, either for Mg2+ or Al3+, increased the adsorption capacity of the calcined samples up to 20%, thus providing indirect evidence in favour of Ti4+ in the brucite layer