Fabrication of size-tunable TiO2 tubes using rod-shaped calcite templates.

Titania tubes with tunable wall thickness were produced by the sol-gel reaction of titanium(IV) n-butoxide in the presence of rod-shaped calcite particles that act as templates. A shell of amorphous titania was deposited around the calcite particles by sol-gel synthesis. The titania was crystallized to the anatase or rutile phase by sintering at different temperatures, and then acid etching was used to remove the calcite core, leaving hollow titania tubes. The influences of several parameters on the final particle formation were investigated, including calcite templates, surfactant, the method of adding reagents, and catalyst. The average width of the prepared titania tubes ranges from nearly 100 nm to 1 microm, with wall thickness ranging from approximately 70 to 300 nm. A possible growth mechanism of the titania tubes is presented. The ability to control titania tube size and crystal structure is important for photocatalysis, photovoltaics, and other applications. The fabrication approach presented is applicable to form tubes of other oxide materials by sol-gel synthesis.