Morphology Controlled Synthesis of γ-Al(2)O(3) Nano-Crystallites in Al@Al(2)O(3) Core–Shell Micro-Architectures by Interfacial Hydrothermal Reactions of Al Metal Substrates

Fine control of morphology and exposed crystal facets of porous γ-Al(2)O(3) is of significant importance in many application areas such as functional nanomaterials and heterogeneous catalysts. Herein, a morphology controlled in situ synthesis of Al@Al(2)O(3) core–shell architecture consisting of an Al metal core and a porous γ-Al(2)O(3) shell is explored based on interfacial hydrothermal reactions of an Al metal substrate in aqueous solutions of inorganic anions. It was found that the morphology and structure of boehmite (γ-AlOOH) nano-crystallites grown at the Al-metal/solution interface exhibit significant dependence on temperature, type of inorganic anions (Cl(−), NO(3)(−), and SO(4)(2−)), and acid–base environment of the synthesis solution. Different extents of the electrostatic interactions between the protonated hydroxyl groups on (010) and (001) facets of γ-AlOOH and the inorganic anions (Cl(−), NO(3)(−), SO(4)(2−)) appear to result in the preferential growth of γ-AlOOH toward specific crystallographic directions due to the selective capping of the facets by adsorption of the anions. It is hypothesized that the unique Al@Al(2)O(3) core–shell architecture with controlled morphology and exposed crystal-facets of the γ-Al(2)O(3) shell can provide significant intrinsic catalytic properties with enhanced heat and mass transport to heterogeneous catalysts for applications in many thermochemical reaction processes. The direct fabrication of γ-Al(2)O(3) nano-crystallites from Al metal substrate with in-situ modulation of their morphologies and structures into 1D, 2D, and 3D nano-architectures explored in this work is unique and can offer significant opportunities over the conventional methods.