Nano-alumina with hierarchical structure has recently attracted extensive attention because of its synergism and coupling effect on micro-nano scales. In the paper, the hierarchical structures of nano-alumina reported in the literature have been divided into four main types including hollow sphere, core-shell, cluster, and array. The progress of their synthesis techniques has been reviewed. Several factors affecting the morphology of nano-alumina particles with hierarchical structure in the course of synthesis have been discussed. It has been recognized in the literature that a majority of effects could be altered if changing the synthesis environment, indicating the complexity of hierarchical structure formation. Nevertheless, there is a general rule for the effect of pH in the hydrothermal process on the morphology of the secondary structure of nano-alumina. Acid condition favors the formation of one dimensional nano-alumina while basic condition helps to form two dimensional nano-alumina. The formation mechanism of the hierarchically structured nano-alumina has briefly been explained. Additionally, the effect of hierarchical morphology on the thermal stability of alumina has been depicted using available results presented in the literature. Some examples of the material applied to the areas of luminescence, adsorption and catalysis have been given in the paper. As viewed from the combination of the rational synthesis and the practical applications of the material with specific properties, the prospects of the research on the hierarchically structured nano-alumina have been outlined in the end of the paper. Contents
1 Introduction
2 Synthesis of hierarchically structured nano-alumina with different morphologies
2.1 Hollow structure
2.2 Core-shell structure
2.3 Cluster structure
2.4 Array structure
2.5 Other structures
3 Synthesis factors and structure formation mechanism
3.1 Factors in morphology forming
3.2 Formation mechanism of hierarchical structure
4 Influence of hierarchical structure on material thermostability
5 Application of hierarchically structured nano-alumina
6 Prospects