Hierarchically structured functional materials: Synthesis strategies for multimodal porous networks

Hierarchically porous materials displaying multimodal pore sizes are desirable for their improved flow performance coupled with high surface areas. In the last five years, a tremendous amount of research has focused upon the synthesis and applications of hierarchically porous materials. This review aims to open up a new avenue of research in this exciting field. At first, recent progress in the synthesis of hierarchically porous materials, targeted through templating methods, is reviewed. These synthesis methods involve a supermolecular assembly of amphiphilic polymers or surfactants combined with second surfactant systems or with macrotemplates such as solid particles, liquid drops, and air bubbles. The preparation procedures using surfactants combined with other chemical or physical methods, controlled phase-separation, or template replication will also be discussed. Subsequently, an innovative procedure concerning the self-formation of hierarchically porous materials is thoroughly examined. This self-formation procedure is based on a self-generated porogen mechanism. Porogens such as alcohol molecules can be precisely controlled at the molecular level to design new hierarchically porous materials. Most of these synthesis methods allow an easy and independent adjustment to the multiporosity of a material, i.e., its micro-, meso-, and macroporosity.