| Summary: | 碩士 === 國立東華大學 === 光電工程研究所 === 97 === Titanium dioxide (TiO2) has been proved to be an effective photocatalyst because of its beneficial physical and chemical properties. According to our previous experiments, titanium dioxide containing carbon could have mixed phase, when it is annealed at low temperature. The mixed phase has better photocatalytic activity compaved to pure Anatase phase in the visible light range. In this study, Anatase phase transforms to the mixed phase assisted by carbon. To realize how carbon assists the TiO2 phase transformation. We analyized samples using Raman spectruscopy at different laser powers to understand the phase transformation assisted by carbons.
In this work, different kinds of carbon (CNT, graphite)were added to pure Anatase phase UV100 (TiO2 containing amorphous carbon) powder, and annealed the samples at different temperatures in air or in low vacuume (10-3 torr). Ranman spectroscopy was used to observe the carbon effect for TiO2 phase transformation. In another part, we annealed the pure UV100 in high vacuum (10-7 torr) and low vacuum (10-3 torr), then cooled down to the room temperature to perform the Raman measurements with different laser powers (0.09~5.96 mW). Last we analyized all the samples with X-ray photoelectron spectroscopy (XPS) to compare with Raman spertra. In this experiment, the role of carbon were analyzed, and the role of laser power in the phase transformaiton was also discussed.
From the XPS spectra of TiO2, pure UV100 was annealed at different temperatures in the same vacuum, the structure of the carbon became different. When UV100 was annealed in low vacuum, peak C=O intensity increased when annealing temperature increased, and the structure of TiO2 existed. When UV100 was annealed in high vacuum at 880℃, peak C-C and C=C intensity increased, and structure of TiO2 existed. In the Raman spectra,under low laser power (0.09 mW), Anatase phase transforms to Rultile phase when UV100 was annealed at 800℃ in low vacuum (10-3 torr). There is no phase transformaiton when the annealing temperature was below 800℃. Under Raman measurement at low laser power, there was no phase transformation when UV100 was annealed at 400~880℃ in high vacuum (10-7 torr). From the resutlt of Raman measurement with high laser power (5.96 mW) and pure UV100 was annealed in low vacuum at 400℃, Anatase phase transforms to mixed phase. When annealing temperature is over the 700℃, we only observe Rutile phase in samples using Raman spectroscopy at high laser power. When pure UV100 was annealed in high vacuum at 400℃, there is no phase transformation using Raman spectroscopy at high laser power. When the annealing temperature is higher than 700℃, we observe Anatase phase transforms to mixed phase. This study assisted us to understand completely visible-light excited mixed phase of TiO2 carbon containing.
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