Nanocasting and nanocoating

The use of organic templates for the controlled structuring of in-organic materials is being widely explored. Two processes, nanocasting and nanocoating, will be discussed in this chapter for the formation of porous metal oxide structures with an emphasis on silica and titania. The diffirence between the two techniques is that casting is a filling of the porous structure of the organic material whereas coating results in a layer of the inorganic substance on the polymer structure. Following formation of the hybrid, the organic template can be removed, yielding a structured inorganic material. Either an inverse replica of the initial structure is obtained after nanocasting or a hollow replica of the organic results with the nanocoating procedure. The initial organic molds considered here are "rigid", preformed matrices or discrete entities that do not require the presence of the inorganic material for producing or maintaining their structure. These range from monolithic materials, including porous polymer gels and colloidal crystals, to organic fibers, crystals, and latex particles. The fabrication methods discussed that are used to obtain the metal oxide structures include sol-gel procedures and the use of preformed metal oxide nanoparticles.