Effective use of flexible low-dimensional colloidal particles and colloidal crystals for the control of hierarchically porous materials

Abstract

Hierarchically porous materials are useful materials because characteristics of pores in various length scales (e.g., micro-, meso-, and macropores) can synergistically be integrated in a material. In this review, preparation of hierarchically porous materials by templating methods is summarized from the viewpoint of flexibilities of colloidal particles and colloidal assemblies as building blocks and templates, respectively. Low-dimensional colloidal particles, such as nanosheets and nanotubes, are used as flexible building blocks to form three-dimensional networks on templates with few defects. Because such colloidal particles can have inter- and intraparticle pores, their assembly on templates is effective to form pores in various length scales. Colloidal crystals, assemblies of uniform colloidal particles, have been used as templates of macroporous and hierarchically porous materials. Recently, the use of colloidal crystals as flexible templates is reported and attracts much attention. A stress due to confined growth of gold within the interstices of the colloidal crystals causes their structural changes, retaining their periodic structure, which direct one- or two-dimensional growth of gold. It is regarded as a novel concept for the preparation of hierarchical nanostructured materials with high crystallinity. The utilization of flexibilities of colloidal particles and colloidal assemblies is promising for the creation of hierarchically porous materials with unique nanostructures.