Modification Of Titanate Oxidation Fibers And Their Photocatalytic Activity

Living standards increasing, people are more and more strict with the quality of drinking water. On the other hand, the civilian, commercial and defence sector of most nations are faced with a tremendous set of environmental problems related to the remediation of hazardous wastes, contaminated water and the control of toxic air contaminants. Removal and recovery of volatile organic compounds (VOCs), especially the chlorinated organics, from drinking water and industrial wastewater has become increasingly important due to stringent environmental regulations. Photocatalysis is an attractive low-temperature, non-energy-intensive approach for treating halogenated organics. Heterogeneous photocatalytic oxidation process involves the use of a photoactive n-type semiconductor illuminated with near-UV light. The application of illuminated semiconductors for the remediation of contaminants has been used successfully for a wide variety of compounds. TiO₂ photocatalysis has been the focus of numerous investigations in recent years due to its optical and electronic properties, low cost, chemical stability and non-toxicity. The activity of the photocatalyst plays an important role in the photocatalytic process. Surface modification can change surface properties of TiO₂ and is very effective in improving the photocatalytic activity of TiO₂, because the photocatalytic activity is mainly dependent on the surface properties of TiO₂. In this thesis TiO₂ fibers were prepared from K2Ti4O9 fiber precursors by ion-exchange reaction in the chlorhydric acid. The obtained TiO₂ fibers were modified by two means—hydrothermal and Pt doping. When undergoing hydrothermal modification, TiO₂ fibers' change of crystal forms under different methods were observed and their photocatalytic activity was investigated. It showed that it was more convenient for H2O hydrothermal than C3H8O3 hydrothermal to make the transformation of TiO₂'s crystal form. At 240℃,titanic acid hydrations from either H2O or C3H8O3 hydrothermal treatment are mainly in H2Ti8O17form. When titanic acid hydration was treated at 240℃,they would turn into TiO₂ fibers. Photocatalysis reaction showed that H2O hydrothermal treated TiO₂fibers were more active than those were treated by C3H8O3 hydrothermal.Pt doped TiO₂ fibers (Pt/TiO₂ fibers) with different Pt content were prepared using photoreductive deposition method. TiO₂ fibers (2.00 g) were suspended in a mixture of 200 mL of platinzing solution (different H2PtCl6 content in a aqueous isopropanol solutions). This suspension was thoroughly flushed with nitrogen to remove oxygen and CO₂. The reaction mixture was irradiated with a 300 W mercury vapor lamp for 3 h. Pt/TiO₂ fibers were obtained after filtrating and heating the filter cake at 120 ℃ for 24 h. The products were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and BET areas.The photocatalytic degradation of chloroform was investigated in aqueous suspension of Pt/TiO₂ fibers over the wavelength range of 310-380nm. The overall rate of CHCl3 degradation increased drastically when the Pt content increased from 0.1 to 0.5 wt% and then decreased by further doping. Compared with the native TiO₂ fibers, Pt/TiO₂ fibers enhanced the reaction notably and the effects of the Pt content, O₂ and pH on the reaction were investigated. The results showed that the maximum rate of CHCl3 degradation could be reached at 98.44% when Pt content was 0.5wt%, pH=5, O₂ was pre-saturated and the initial concentration of CHCl3 and Pt/TiO₂ was 1 mmol/L and 0.5 g/L respectively. Under the same conditions, the rate of CHCl3 degradation was 72.03% when Pt/TiO₂ granules were used.