Results and Discussion
Characterization of TiO2 Nanocrystals
The thermal decomposition process of the TiO2 Sol-gel after preheating (40 °C, 24 h) and during calcination in air was studied using DTA/TG. The results are shown in Fig. 2. As can be seen, the total weight loss of the sol-gel from 30 to
Fig. 2 DTA/TG curves of the TiO2 nanocrystal precursor of the sample
800 °C amounts to 70%. The decomposition process can be divided into four stages. The temperature range in the first, second and third stage is 30-110 °C, 100-250 °C and 250-450 °C, respectively. The weight loss in each stage is about 5.2, 13.77, and 35.05%, which can be correspondingly attributed to the removal of water, the evaporation of organic solvents and the combustion of the organic materials of the framework of the sol-gel. On the DTA curve, no strong significant thermal effect was observed in the second and third stage. The last stage is in the temperature range of 450-800 °C. The corresponding weight loss is 16.66%. On the DTA curve, an endothermic peak at 550 °C appears, which signifies the formation
Fig. 3 a XRD patterns of TiO2 Films at 300-700 °C for 2 h. b XRD patterns of TiO2 films at 700 °C from 3 to 600 min of TiO2 or phase transition. The weight loss in this stage is probably due to the removal of carbon materials.
XRD patterns of the TiO2 film obtained via sintered at different conditions are shown in Fig. 3a and b. With increasing calcination temperature from 300 to 700 °C (duration = 2 h), the XRD results of TiO2 film shows the peak ratio of XRD patterns between anatase and ITO increased.
Figure 3a indicates that the calcination temperature (300-500 °C with 2 h soaking time) is not high enough that the TiO2 grain be completely sintered.
By increasing soaking time from 3 min to 600 min (T = 700 °C), Fig. 3b indicates that upon calcination at 700 °C for more than 100 min’s, the peak intensity is sharper and narrower than that of the times less than 100 min. This implies that thermal aging (>100 min) at a temperature of as high as 700 °C is necessary for the completely crystallization of TiO2 and the complete removal of carbon from the product. (For comparison, the peak ratio of XRD patterns between anatase and ITO (indium tin oxide) are used).