Influence of calcining temperature on photoresponse of TiO2 film under nitrogen and oxygen in room temperature

The photoresponse of TiO2 in nitrogen and oxygen under visible light was studied. The TiO2 was synthesized by a new sol–gel process using Ti(OBu)4 and ethanolamine, while the research was focused on the effect of calcining temperature on the photoresponse of the TiO2 film. It was observed a strong photoresponse of the TiO2 at a light wavelength of approximately 480 nm in room temperature when calcined at temperature from 450 to 500 °C. On the contrary, the photoreponse was very weak for TiO2 calcined at temperature less than 400 °C or more than 550 °C. Thermal gravimetry–differential scanning calorimeter–mass spectrometer (TG–DSC–MS) measurement showed that there was a significant weight loss (about 18 wt.%) of the TiO2 precursor calcined in the temperature range from 400 to 470 °C, which was due to the oxidation of the residual impurities in the TiO2. The evolved gases were primarily composed of H2O and CO2. In conclusion, it is suggested that the strong photoresponse of the TiO2 under visible light is due to the impurities, such as carbon or hydrocarbon compound which mixed with or adhered on the TiO2, as well as the microporous structure in the TiO2 film.