Simultaneous Control of Phase Transformation and Crystal of Amorphous TiO2 Coating on MWCNT Surface

Abstract

We developed a mass production method that simultaneously controls the phase transformation and crystal size of TiO2 coatings on multiwalled carbon nanotubes (MWCNTs). Initially, MWCNTs were successfully coated with amorphous 15-20-nm-thick TiO2 by an in-situ sol-gel method. As the calcination temperature increased in both air and argon atmospheres, the amorphous TiO2 was gradually transformed into the fully anatase phase at approximately 600 degrees C, a mixture of the anatase and rutile phases at approximately 700 degrees C, and the fully rutile phase above approximately 800 degrees C. The crystal size increased with increasing calcination temperature. Moreover, above 600 degrees C, the size of crystals formed in air was approximately twice that of crystals formed in argon. The reason is thought to be that MWCNTs, which continuously supported the stresses associated with the reconstructive phase transformation, disappeared owing to complete oxidation in air at these high temperatures.