Abstract: Nano Mg-Al LDHs were prepared by a hydrothermal method in one step. Effects of precursors, alkalinity of the starting solution, temperature and time on phase purity and crystallite sizes of Mg-Al LDHs were systematically investigated. Reaction products were characterized by powder XRD and SEM. Crystallite sizes of Mg-Al LDHs were determined by the X-ray whole powder pattern fitting method. The optimal parameters for preparing Mg-Al LDHs are keeping the ratio of MgO:Al(OH)₃:Na₂CO₃=2:1:1
at 140℃ for 4h to 10h. The formation mechanism proposed for Mg-Al LDHs is dissociationprecipitiationcrystal growth. The reactant type and hydrothermal conditions may influence the dissociation rate of the precursors, nucleation and growth rates of Mg-Al LDHs, as well as phase combination and crystallite sizes of the reaction products.

Key words: nano crystallites, Mg-Al LDHs, hydrothermal synthesis, whole powder pattern fitting, formation mechanism