Influencing the texture and morphological properties of layered double hydroxides with the most diluted solvent mixtures – The effect of 6–8 carbon alcohols and temperature

Abstract

Three layered double hydroxides (MgAl-, CaAl- and CaGa-LDH) were obtained via co-precipitation with NaOH as base, and the effects of ageing in the slurry at elevated temperatures were under investigation. As expected, the crystallinity of the products improved after ageing, and the particle diameter of the Ca-containing samples grew as well. The experiments were carried out in the presence of either 1-hexanol, 1-heptanol or 1-octanol during the LDH formation. Each alcohol, functioning as a co-solvent in low concentration, had the same impact on the crystalline properties of the product: the morphology of all LDHs improved and the diameter of the CaM-LDH particles (M = Al, Ga) increased from the original 100–300 nm to 1–3 μm without ageing to an immense 5–10 μm after treatment at 60 °C. Small changes were detected in the X-ray traces, the basal spacing of the CaM-LDHs shrank. Considering the presence of large alcohol molecules in the interlamellar space, one may predict a rise in the basal spacing, however, it is also a function of the hydration degree of the interlayer space. Since alcohols with 6–8 carbon atoms are regarded as hydrophilic ones, we attribute the smaller interlayer distance to the partial exclusion of water from the interlamellar space. This phenomenon was confirmed via thermogravimetry. The difference in the size of alcohol and heat-treated CaM-LDHs to MgAl-LDH presumably arise from the stronger interaction of calcium ions with structural alcohol molecules due higher coordination number of the calcium ion (7) in the corresponding LDHs than that for the magnesium or aluminium ions (6).