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The template method for synthesizing nanostructures involves the synthesis of the desired material within the pores of a nanoporous membrane or other solid. Our work has involved using porous alumina and polymeric filter membranes as the templates. Fibrils or tubules of the desired material are formed within each pore of the template membrane. A number of synthetic methods have been used to synthesize these nanostructures. This paper reviews sol-gel template synthesis: the use of sol-gel chemistry to synthesize semiconductor oxide micro-and nanostructures within the pores of micro-and nanoporous membranes. For example, TiO 2 nanotubules and nanofibers of the anatase form have been synthesized. The high surface area offered by these TiO 2 nanostructures has been used for photodecomposition of salicylic acid in sunlight. Enzyme immobilization by stannous bridges inside the TiO 2 tubes has also been studied. In addition, V 2 O 5 fibrous electrode materials have been prepared by this method and Li intercalation electrochemistry is reported here. Other semiconductor oxides such as MnO 2 , Co 3 O 4 , ZnO, WO 3 , and SiO 2 have also been prepared.

The template method for preparing nanostructures entails synthesis of the desired material within the pores of a nanoporous membrane or other solid. A nanofibril or tubule of the desired material is obtained within each pore. Methods used previously to deposit materials within the pores of such membranes include electrochemical and electroless deposition and in situ polymerization. This paper describes the first use of sol-gel chemistry to prepare semiconductor nanofibrils and tubules within the pores of an alumina template membrane. TiO 2 , WO 3 , and ZnO nanostructures have been prepared. TiO 2 nanofibrils with diameters of 22 nm were found to be single crystals of anatase with the c-axis oriented along the fibril axis. Bundles of these fibrils were also found to be single crystalline, suggesting that the indiviual fibrils are arranged in a highly organized fashion within the bundle. Finally, 200 nm diameter TiO 2 fibrils were used as photocatalysts for the decomposition of salicylic acid.

We have developed a new approach for preparing graphitic carbon nanofiber and nanotube ensembles. This approach entails chemical vapor deposition (CVD) based synthesis of carbon within the pores of an alumina template membrane with or without a Ni catalyst. Ethylene or pyrene was used in the CVD process with reactor temperatures of 545 °C for Ni-catalyzed CVD and 900 °C for the uncatalyzed process. The resultant carbon nanostructures were uniform hollow tubes with open ends. Increasing the deposition time converted the carbon nanotubes into carbon nanofibers. Transmission electron microscopy and electron diffraction data show the as deposited graphitic carbon nanofibers synthesized with the Ni catalyst were not highly ordered. Heating the carbon-containing membrane at 500 °C for 36 h, however, converts the carbon nanofibers into highly ordered graphite. The electron diffraction data show a spotted diffraction pattern characteristic of single-crystal graphite with the graphitic planes parallel to the long axis of the nanofibers.

Ensembles of highly aligned and monodisperse graphitic carbon nanotubules have been prepared via the template method using chemical vapor deposition of carbon within the pores of alumina membranes. Tubules with diameters of 200 nm have been prepared, and smaller diameters are possible. Free-standing aligned carbon-tubule membranes are formed by this template method. These novel carbon tubule membranes can be filled with nanoparticles of electrocatalytic materials (i.e., Pt, Ru, Pt/Ru), which can then be used to electrocatalyze O2 reduction and methanol oxidation as well as the gas-phase catalysis of hydrocarbons. Hence, these membranes have potential applications in fuel cell development. Smaller, highly ordered graphitic-carbon tubules can also be prepared within the template-synthesized carbon tubules, using Fe nanoparticles as catalysts. In these novel tube-in-tube structures, both the outer and the inner tubules are electrochemically active for Li+ intercalation, suggesting possible applications such as Li ion battery anodes.