Anatase phase formation kinetics in Ti and TiOx nanoparticles produced by gas-phase condensation

Anatase TiO2 nanoparticles were successfully synthesized by post-heat treatments of partially crystalline Ti and amorphous TiOx nanoparticles, respectively produced by inert gas condensation and subsequent oxidation. The nanoparticles condensed on a liquid-nitrogen containing cooling finger (sample LN) were identified to be partially crystalline Ti phase with similar to 10-20 vol.% amorphous TiOx. On the other hand, those condensed on a room-temperature cooling finger (sample RT) were almost completely amorphous TiOx phase. Differential scanning calorimetry scan curves of as-oxidized samples were interpreted using Kissinger analysis, the non-isothermal kinetics, and activation energy for the anatase formation was determined as similar to 455 and 865 kJ/mot for samples LN and RT, respectively. As-oxidized samples LN and RT were heat treated at 400 degrees C for 2 h, respectively (samples LN-H and RT-H). Samples LN-H and RI-H showed the onset of UV-visible light absorption near 400 nm and the optical band gap of 3.12 and 321 eV, respectively, corresponding to anatase. The sample LN-H showed faster photocatalytic decomposition of methylene blue and rhodamine B dyes compared to the sample RI-H due to high crystallinity of anatase and rutile phases. (C) 2011 Elsevier B.V. All rights reserved.