Template-directed synthesis of oxide nanotubes: Fabrication, characterization, and applications

A template-directed synthesis strategy is an ideal tool to fabricate oxide nanotubes in that their physical dimensions can be precisely controlled and monodisperse samples can be harvested in large quantity. The wall thickness of the oxide nanotubes is controllable by varying the deposition conditions, and the length and diameter can be tailored in accordance with the templates used. A wealth of functional oxide materials with the controlled polymorphs can be deposited to be nanotubular structures by various synthesis methods. This short review article describes the recent progress made in the field of the template synthesis of oxide nanotubes. We begin this review with the comprehensive survey on the research activities of the template-directed oxide nanotubes. We then focus on the template synthesis that combines porous membrane templates with various deposition techniques and discuss the processing issues associated with coating inside nanoscale pores, selective etching of oxide nanotubes from the templates, and dispersion against the formation of nanotubes' bundle-up. Structures and physical properties of the oxide nanotubes prepared by template synthesis are also summarized. Their potential for application in drug-delivery systems, sensors, and solar energy conversion devices, which could be facilitated by the template synthesis, is discussed. Finally, we conclude this review as providing our perspectives to the future directions in the template-directed oxide nanotubes.