Synthesis of Porous Materials and Their Microstructural Control through Ice Templating

Abstract

Ice-templating is a simple, practical kind of template synthesis which consists of sol-gel polycondensation, unidirectional freezing of hydrosols or hydrogels, and pore-preserving drying method, such as freeze drying, thereby resulting in desirable porous materials. The unidirectional freezing may be achieved by either immersion freezing or contact freezing. Freeze-dried materials contain porous microstructures that are replicas of the ice crystals formed during the unidirectional freezing process. Two similar but slightly different applications of ice-templating will be investigated here. Fabrication of macroporous foam materials by unidirectional freezing of an aqueous suspension of carbon nanotubes (CNTs) dispersed by chitosan is a concrete example of functionalization of an electroconductive foam, which is a composite material made from a polymer and CNTs. As expected, their electroconductive properties can be controlled by the fabrication method and condition. Additional examples of porous materials synthesized by ice-templating are porous microfibers and microhoneycombs of silica, titania, silica-alumina, titania-silica, and even carbon. In the preparation, the morphology and porous structure can be controlled by the freezing conditions and synthesis conditions of the corresponding hydrogels, respectively.