Synthesis and characterization of anatase TiO{sub 2} nanotubes with controllable crystal size by a simple MWCNT template method

Highly crystalline phase-pure anatase TiO{sub 2} nanotubes were produced by performing a simple calcinations process in air of the TiO{sub 2} coated MWCNTs composite material prepared by an in situ sol-gel method. A homogeneous thin coating layer of TiO{sub 2} on the surface of MWCNTs is firstly obtained. Calcination in ambient air at appropriate temperatures is performed to transform phase of TiO{sub 2} into anatase and remove MWCNTs simultaneously, resulting in pure anatase TiO{sub 2} nanotubes. Both end tips of the nanotubes are observed to be closed, probably due to covering up MWCNTs with TiO{sub 2} particles. The crystallization of anatase phase was formed upon 350 Degree-Sign C, and MWCNTs are completely oxidized between 500 and 650 Degree-Sign C, leaving anatase TiO{sub 2} 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 Degree-Sign C. - Graphical abstract: TGA analysis and TEM images of the samples after calcinations in air at different temperatures: (a) before calcinations, (b) 350 Degree-Sign C, (c) 500 Degree-Sign C, and (d) 650 Degree-Sign C. Highlights: Black-Right-Pointing-Pointer Highly crystalline and stable phase-pure anatase TiO{sub 2} nanotubes were produced by a simply MWCNT template method. Black-Right-Pointing-Pointer A homogeneous thin coating layer of TiO{sub 2} on the surface of MWCNTs could be obtained. Black-Right-Pointing-Pointer Small crystal size of anatase is formed at lower temperatures and higher temperatures cause significant increase of crystal size from 8 to 24 nm. Black-Right-Pointing-Pointer Convex closed tip structure of TiO{sub 2} nanotubes is formed owing to the good coating of TiO{sub 2}.