Perturbing the properties of layered double hydroxides by continuous coprecipitation with short residence time

A previous work (S. Abello and J. Perez-Ramirez, Adv. Mater., 2006, 18, 2436) revealed an unanticipated variation in the textural properties of Mg-Al hydrotalcite, prepared by continuous coprecipitation with short residence time, tau = 1 s which, at that time, was not fully understood. Herein, we report the generalisation of such variation in physical properties to layered double hydroxides (LDHs) of different composition (Ni-Al, Mg-Al, and Mg-Fe hydrotalcite-like compounds). In particular stable colloidal suspensions and, on drying, impervious LDH particles have been prepared using the in-line dispersion precipitation (ILDP) method with tau = 1 s. This is thought to be a consequence of variation in the mechanism of inter-crystallite interactions with decreasing crystallite size. The resulting materials are characterised using multiple techniques and are compared to analogous materials attained at longer residence times (tau = 12 s). We show that despite the apparent compositional similarity and structural isomorphicity of the precipitates, their textural and morphological properties and their thermal stability differ strongly. Thermal activation of the LDHs, however, resulted in the development of comparable textural properties in the corresponding oxides, independent of the residence time.