Solution synthesis strategies for hierarchical nanostructures

The coupling and synergistic effects of the unique structure of multi-level, multi-dimension, and multi-components allow for the directed synthesis of hierarchical nanostructures and this field has attracted much interest recently. In this paper, we discuss progress in the solution synthesis of three kinds of hierarchical structures including core-shell, segmented, and branched structures. We focus on the formation mechanism and the influencing factors of the hierarchical structures by considering the crystal nucleation-growth process and growth kinetics. The construction of the hierarchical nanocomposites mainly involves the heterogeneous nucleation-growth of the secondary structures on the primary structures or a component exchange between the two kinds of materials. The degree of lattice matching, the degree of supersaturation, and chemical bonding mainly influence the hetero-nucleation sites of the secondary structures on the primary structures. The growth behaviors of the secondary structures can be modulated mainly by adjusting their crystallographic energy through surface modifications. For the synthesis via component exchange, an important prerequisite is that the primary and secondary structures share the same anions or cations.