Formation of Hierarchically Porous Metal Oxide and Metal Monoliths by Nanocasting into Silica Monoliths

The formation of hierarchically porous metal and metal oxide monoliths by replication of hierarchically porous silica templates is reviewed. The various factors that impact the structure and properties of the synthesized materials are discussed and illustrated by the formation of new a-Fe2O3, ZrO2, nickel, silver, and silver silicate porous monoliths. The impact of the atmosphere is addressed in the formation of Co3O4 and silver monoliths. For Co3O4, formation of the monolith under vacuum, air, argon, or nitrogen was found to dramatically change the structure of the final material. For silver, decomposition of the silver nitrate under air resulted in porous monoliths composed of silver silicates. Decomposition of silver nitrate under vacuum produced monoliths for which the chemical composition of the monolith was predominantly silver on the exterior of the monolith consisted of silver silicates in the interior of the monolith.