Synthesis of layered double hydroxide coatings with an oriented structure and controllable thickness on aluminium substrates

Layered double hydroxides (LDHs) are applied in environmental purification and biomedicine because of their anion intercalation and exchange properties. This study investigates the formation of LDH layers on aluminium substrates, through the reaction of substrates in solution containing magnesium ions at 30-90 degrees C. The resulting LDH layer was constructed from many plate-shaped crystals. The LDH crystal size increased with increasing reaction temperature. The LDH layer was preferentially oriented perpendicular to the substrate, thus the LDH crystal orientation was out-of-plane. The oriented structure was formed by crystal-growth-controlled geometrical selection. The LDH layer growth rate also increased with increasing reaction temperature. A high reaction temperature (90 degrees C) resulted in rapid formation of an approximately 10 mu m-thick LDH layer. Milder temperatures (30 and 60 degrees C) resulted in a moderate LDH layer growth rate, which allowed the LDH layer thickness to be precisely controlled. The LDH layer removed toxic fluoride anions from aqueous solution without damaging the layer. These findings promote the development of oriented LDH coatings with precisely controlled microstructures and thickness.