Synthesis and identification of hierarchical γ-AlOOH self-assembled by nanosheets with adjustable exposed facets

Abstract

The orientation of exposed crystal facets is of great significance for the materials to play a role in the processes of adsorption and catalysis. However, it is awkward to adjust and identify the proportions of various exposed facets quantitatively, especially with regard to hierarchical materials. In this study, the synthesis of two types of hierarchical γ-AlOOH materials both self-assembled by secondary nanosheets but with different dimensions was achieved facilely by a hydrothermal method. The proportions of the three primary exposed facets on two types of nanosheets were adjusted by changing solvent and anion type, and their values were calculated on the basis of a fine structure reconstruction simulation. The results reveal that both types of secondary nanosheets are monocrystalline mainly exposing the (010) plane along with the anisotropic growth in order of [001] > [100] > [010]. In the SO₄²⁻/water synthesis environment, the nanosheets display less (010) surface but more (100) and (101) surfaces than those formed in the NO₃⁻/water–ethanol system. The evolution of the hierarchical γ-AlOOH architecture was also discussed and a structure unit-oriented attachment mechanism was suggested to explain the growth of nanosheets.