Metal oxides, template-directed crystallization

In another approach Subramanian et al. [32] infiltrated the polymeric opal template directly with ultrafine particles instead of employing metal alkoxides or salts. In this approach infiltration with a nanocrystalhne material of known crystal phase is possible, and therefore materials with a predetermined crystal structure of the walls can be obtained even at mild processing conditions. For instance, Ti02 frameworks with a rutile phase of the wall material could be obtained without the necessity to resort to sintering at high temperatures. Additionally, shrinkage, which commonly occurs in the case of condensation of metal alkoxides or conversion of metal salts, is largely reduced. Finally, this route opens a pathway to obtain porous metal oxide materials, which are barely accessible by wet chemistry approaches. 

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