Homogeneous Precipitation of Mg/Al Layered Double Hydroxide from Concentrated Metal Salt Solution Under Hydrothermal Conditions

Homogeneous precipitation using urea hydrolysis under hydrothermal conditions has been examined to prepare carbonate type magnesium aluminium layered double hydroxides (Mg/Al-CO3 LDHs). To obtain well-crystallized Mg/Al-CO3 LDHs as single phase, low concentration starting solutions have been used, resulting in the small amount of product from a batch. In this study, concentrated starting solution (1.0 M) of magnesium chloride and aluminum chloride was used to achieve bulk syntheses. The reaction conditions were optimized to obtain well-crystallized Mg/Al-CO3 LDH of rosette-like shape with the radius of ca. 2-4 μm in a large scale (7.6 g from 160 mL container). The parameters including heating rate and reaction temperature were found to be important to avoid the formation of by-products, and the Mg/Al ratio in the initial solution influenced the composition and morphology of the products. The heating rate of 8 oC/min and the reaction temperature at 100oC successfully led single-phase Mg/Al LDHs.