Roles of interfaces in nanostructured composites: nanocatalysts, sponge crystals and thin films

Interfaces are important in the functionality of materials with composite structures. Focusing mainly on our studies, this article provides an overview of the functionality that can be achieved by the careful design of interfaces in inorganic composites. Molecular selective photocatalysts have been realized by developing nanostructures, in which photocatalytically active metal oxide particles are surrounded by mesoporous silica. Such composites structure achieved combined function of molecular selective adsorption and photocatalytic decomposition. Solid acid catalysts that are active in water have been realized by exploiting the nanostructure of mesoporous silica. Catalytically active inorganic molecules such as heteropolyacids have been anchored on the walls within the pores of hydrophobic organic layers. The resulting nanocomposite exhibited high acid catalytic activity in water. Sponge crystals are a more recently discovered class of porous crystals. We discuss their structure, and propose revised classifications of microporous crystals, mesocrystals and sponge crystals. Thin films of metal nitrides such as Sr2N and metal oxides have been prepared by molecular beam epitaxy and pulsed laser deposition. The effects of the interface between the film and substrate are discussed.