Abstract
Silica nanotubes have been found to be highly valuable as nanoscale host materials in bioanalysis, biocatalysis, and bio-separation. Harada and Adachi first developed a surfactant-mediated technique for the synthesis of silica nanotubes. Wang et al. observed the formation of tubular silica on silicon particle seeds during a high-temperature process. Until now, several template-originating techniques have also been developed for the preparation of silica nanotubes. Zhang et al.used a template-assisted sol-gel method to form pure SiO2 nanotubes in a porous alumina membrane. Kovtyukhova et al. employed a two-step process for the preparation of SiO2-Au nanocables, forming SiO2 nanotubes by a sol-gel method first and then depositing Au in the hollow cavities, and demonstrated that the SiO2 sheath has a perfect insulating effect. Yin et al. and Yang and coworkers used Ag and Si nanowires, respectively, as templates to prepare filled SiO2 nanotubes, and then removed the cores from the nanocables to obtain pure, hollow SiO2 nanotubes. In addition, Hu et al. reported the thermal evaporation of SiO powders that led to the formation of silica nanotubes/nanowires, even though the formation mechanism of the tubular nanostruc-tures was not fully determined.