Size and Morphology Controlled Synthesis of Boehmite Nanoplates and Crystal Growth Mechanisms

The aluminum oxyhydroxide boehmite is an important crystalline phase in nature and industry. We report development of a flexible additive-free hydrothermal synthesis method to prepare high quality boehmite nanoplates with sizes ranging from under 20 nm to 5 μm via using hydrated alumina gels and aluminum hydroxide amorphous powders as precursors. The size and morphology of the boehmite nanoplates was systematically varied between hexagonal and rhombic by adjusting precursor concentrations, pH, and the synthesis temperature, due to face-specific effects. The transformation mechanism is consistent with dissolution and reprecipitation, and involves transitory initial appearance of metastable gibbsite that is later consumed upon nucleation of boehmite. Detailed X-ray pair distribution characterization of the solids over time showed similarities in short-range order that suggest linkages in local chemistry and bonding topology between the precursors and product boehmite, yet also that precursor-specific differ...