Synthesis and characterization of anatase TiO2 nanotubes with controllable crystal size by a simple MWCNT template method

Highly crystalline phase-pure anatase TiO2 nanotubes were produced by performing a simple calcinations process in air of the TiO2 coated MWCNTs composite material prepared by an in situ sol–gel method. A homogeneous thin coating layer of TiO2 on the surface of MWCNTs is firstly obtained. Calcination in ambient air at appropriate temperatures is performed to transform phase of TiO2 into anatase and remove MWCNTs simultaneously, resulting in pure anatase TiO2 nanotubes. Both end tips of the nanotubes are observed to be closed, probably due to covering up MWCNTs with TiO2 particles. The crystallization of anatase phase was formed upon 350 °C, and MWCNTs are completely oxidized between 500 and 650 °C, leaving anatase TiO2 nanotubes with an average crystal size increasing from about 8 to 24 nm as the temperature rises. Moreover, the tubular structure was found to collapse after calcinations at 700 °C.