Catalyst-Free Thermal Evaporation Synthesis of TiO2 Nanostructures in Atmospheric Air

TiO2 nanostructures were synthesized using a thermal evaporation method without a catalyst. TiO powders mixed with graphite powders were used as the source materials. The synthesis process was performed in air atmosphere at 1000 degrees C. When the mass ratio of TiO/graphite in the source material was 2:1, TiO2 nanowires and nanobelts started to form. As the mass ratio of graphite to TiO increased to 1:1, TiO2 nanowires and nanobelts were formed in large quantity. The nanowires had an average diameter of 80 nm and lengths in the range of 3 similar to 11 mu m. The average width and length of the nanobelts were 500 nm and 3.4 mu m, respectively. However, with further increase in the mass ratio of TiO/graphite to 1:2, no nanostructures were observed. The mass ratio of graphite to TiO in the source material had an important effect on the formation of the TiO2 nanowires and nanobelts. The X-ray diffraction data confirmed that the TiO2 nanostructures had a rutile crystal structure. Two emission bands centered at 410 nm and 510 nm were observed in the room temperature cathodoluminescence spectrum of the TiO2 nanostructures. The emission at 410 nm is attributed to the electron transition from the conduction band to the valence band in rutile TiO2 crystal, which is indicative of the high crystallinity of the TiO2 nanostructures.