Nanocrystalline titanium dioxide with enhanced thermal stability was prepared by subjecting the alkoxide-derived TiO2 gel to a hydrothermal treatment at 150°C for 3h in dilute HNO3 solution (pH 3 or 2). Structural modifications of TiO2 were analyzed by XRD and the morphology of the powders observed by FE-SEM. The hydrothermal treatment stabilized TiO2 in two ways, i.e., suppressing thermal growth of TiO2 crystallites and shifting up the temperature of anatase-to-rutile phase transformation, although the degree of stabilization differed considerably depending on the pH of the HNO3 solution used. The TiO2 hydrothermally treated at pH 3 consisted of small anatase nanospheres of 13 and 34nm in average diameter after calcination at 600 and 800°C, respectively, whereas the untreated TiO2 was predominated by rutile phase at 700°C. Suppression of crystallite growth was even more conspicuous with the treatment at pH 2; the average crystallite size of anatase was 11 and 26nm after calcined at 600 and 800°C, respectively. In this case, however, the transformation was less hindered, with rutile phase occupying 9, 22 and 67% of TiO2 after calcinations at 600, 700 and 800°C, respectively. This indicates that the phase transformation is not always related uniquely with crystallite size of anatase phase. The thick films fabricated with these TiO2 powders did not show much differences in sensor response (ratio of resistance in air to that in gas) to dilute CO in air at 400-550°C, though the powder hydrothermally treated at pH 3 tended to give the highest response. However, the hydrothermal treatment was found to improve much the sensor response transients, suggesting that it was effective in developing mesopores inside the films.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Surfaces, Coatings and Films
- Metals and Alloys
- Electrical and Electronic Engineering
- Materials Chemistry