Tunable growth of TiO2 nanostructures on Ti substrates

Abstract

A simple and facile method is described to directly synthesizeTiO2 nanostructures on titanium substrates by oxidizing Ti foil using small organic molecules as theoxygen source. The effect of reaction temperature and oxygen source on the formation of theTiO2 nanostructures has been studied using scanning electron microscopy, x-raydiffraction, transmission electron microscopy, Raman spectroscopy and watercontact angle measurement. Polycrystalline grains are formed when pure oxygenand formic acid are used as the oxygen source; elongated micro-crystals areproduced when water vapour is used as the oxygen source; oriented and alignedTiO2 nanorod arrays are synthesized when ethanol, acetaldehyde oracetone are used as the oxygen source. The growth mechanism of theTiO2 nanostructures is discussed. The diffusion of Ti atoms to the oxide/gas interface via the network ofthe grain boundaries of the thin oxide layer is the determining factor for the formation of well-alignedTiO2 nanorod arrays. The wetting properties of theTiO2 nanostructured surfaces formed are dictated by their structure, varying from a hydrophilicsurface to a strongly hydrophobic surface as the surface structure changes frompolycrystalline grains to well-aligned nanorod arrays. This tunable growth ofTiO2 nanostructures is desirable for promising applications ofTiO2 nanostructures in the development of optical devices, sensors, photo-catalysts andself-cleaning coatings.