Insights into hierarchically meso–macroporous structured materials

Abstract

A great deal of progress has recently been made in the field of ordered porous materials having uniform channel dimensions which can be adjusted over a wide range of length scales. Incorporation of macropores in mesoporous materials combines benefits from both the mesoporous and macroporous structures. Hierarchical materials containing both interconnected macroporous and mesoporous structures have enhanced properties compared with single-sized pore materials due to increased mass transport through the material and maintainance of a specific surface area on the level of fine pore systems. Bimodal mesoporous–macroporous inorganic materials can be prepared by using a self-assembling surfactant or amphiphilic block copolymer species in conjunction with macrotemplates such as colloidal crystals, polymer foams, bio-celluloses, emulsions, inorganic salts and ice crystals, or by macroscopic phase separations. Here, we review the state of the art for hierarchical meso–macroporous inorganic materials and their carbon replicas from the viewpoint of synthesis strategies and emerging applications. Detailed synthetic processes are described, in which the very recently developed spontaneous formation of meso–macroporous (single and binary) metal oxides, metal phosphates and aluminosilicates is specifically addressed. These novel meso–macroporous materials have found a number of applications, including HPLC separation, catalysis, fuel cell electrode materials, biomaterials engineering, controlled drug delivery devices, and membrane reactors, and these are discussed illustratively.