Another approach to developing nano-architectured materials, apart from the sol-gel route described above, is template synthesis, i.e. mineralization in the presence of templates. This is based on the application of molds/templates, which serve as the basis for the development of functionalized objects of various shapes, with a high degree of reproducibility.
The versatility of the models that can be used includes: i) colloidal models (e.g. colloidal solutions of SiO2 and others), ii) non-colloidal models (e.g. membranes or even host networks), iii) soft models (macro or microemulsions or even micelles, polymers, peptides), iv) natural models (insect wings, pollen, leaves). These models enable us to design objects/structures whose shape is limited only by our imagination. They are generally produced in three stages: firstly, the surfaces of the models are coated or functionalized; secondly, the models are chemically removed; and thirdly, the resulting materials are post-processed. Hollow spheres of TiO2, Pd, CuS, polymers and other materials can be produced, or in the same spirit, porous oxide crowns or even yolk-shell structures for catalyst support using protective agents. The extension of this approach to the fabrication of ZnAl2O4 nanotubes using Kirkendall effect templates is also reported.
