Preparation Oriented Titanium Oxide Thin Film By Electrophoretic Deposition And Hydrothermal Treatment

Semiconductor materials including titanium oxide that can be applied in photocatalysis technology are getting increasing attention since they become suitable and green solutions for environmental issues. The recent research is focusing on the TiO₂ film because the powder material has various weaknesses such as low activity, agglomeration, difficulty in separation and recycling. However, the common techniques of film fabrication cannot meet requirements of the product's quality and industrial manufacture. In this paper, we used layered titanate HxTi2-x/4â–¡x/4O4·H2O (HTO) as the precursor material, adopted hydrothermal treatment combined with electrophoretic deposition, successfully obtained (101) oriented anatase TiO₂ thin film on the FTO conductive glass and platinum substrate respectively. Additionally, the film's morphology of surface and cross section, phase structure, endothermic character and characteristic of spectrum absorption was investigated by using X-ray diffraction (XRD), scanning electron microscope (SEM), thermogravimetry-differential thermal analysis (TG-DTA) and ultraviolet-visible (UV-VIS) spectrum. The relevant mechanism of EPD process, hydrothermal reaction and photocatalysis was also discussed through corresponding experiments.In the process of EPD, the critical voltage value of commencement for deposition increases with the amount of ethanol in the suspension increasing. And the thickness of film increases with the voltage in the same suspension. The deposition kinetics changes from a linear time (t)-thickness (h) function to a parabolic t1/2-h function. The optimum process parameters are selected as follows: The volume ratio of distilled water to ethanol in the suspension is 1:1, the applied voltage and time is 50 V, 30 min respectively. In this condition, a dense and smooth precursor HTO film with layered structure is obtained.After hydrothermal treatment, the HTO film is transferred to (101) oriented anatase TiO₂ thin film. The phase structure and morphology of TiO₂ film are influenced significantly by solvent, pH value, temperature and duration. Strong acid, alkali and other organic solvents have negative impacts on the formation of desirable phase and structure in the product. The HTO→TiO₂ process occurs between the temperature range of 180℃—200℃. The reaction time is less or more than 24 hours, the crystallinity and purity of the film are decreasing. TiO2 thin film with ideal surface morphology and hybrid phase (the volume ratio of anatase and rutile is 3:1) is obtained when HTO film is hydrothermal treated at 200℃for 24 h in pure water with pH value 7.1.The photocatalytic property of the obtained thin film has been studied. The solvent of Rhodamine B is used as the indicator. In order to compare photocatalytic property of TiO2 film derived from different methods, the film has also been prepared by treateing HTO fim in air at 500℃for 1h. The results show that the activity of hydrothermally- treated film is 30% higher than the calcined sample. It because the former product has a smaller grain size, larger specific surface area and hybrid phase structure contained both anatase and rutile which leads to a better performance in the photocatalytic reaction.