Designing,Preparation,and Photocatalytic Performance Of Novel Oxide Semiconductor Nanocomposite

With the rapid development of industrial civilization, a lot of industrial wastewater is discharged into the environment, which poses a serious threat to the health and survival of human beings. Organic wastewater is the main part of industrial wastewater. The complex component, strong toxicity and chemical stability of organic wastewater make it a difficulty in the environmental purification.The photocatalytic technology has many advantages, such as mild reaction condition, use of solar energy, degradation of most organic compounds, no secondary pollution, and simple reaction apparatus. These features make it a promising candidate in the field of wastewater purification.TiO2is the most widely studied photocatalyst because it has excellent photocatalytic activity. However, it needs multiple reaction steps and complex process control to prepare TiO2with favorite structures. Moreover, TiO2has a good dispersion in an aqueous system, which makes it difficult to be separated from the photocatalytic system. In addition, because TiO2can only absorb ultraviolet light, it cannot make full use of the solar energy. Therefore, it is very important to develop a novel photocatalyst with simple preparation, easy recovery, visible light activity, and high photocatalytic efficiency.In this thesis, we designed and synthesized a series of TiO2@C, TiO2/y-Fe2O3, and α-Fe2O3/y-Fe2O3nanostructured composites. Aiming at resolving the current problems in the field of photocatalysis, we did research on the design of nanostructures, optimization of process, and photocatalytic performance of the prepared materials to explore photocatalysts with a simple preparation method, magnetic recovery and reuse, high photocatalytic activity, and visible light activity. The main contents and results are listed below:1. We developed a novel strategy to prepare anatase/rutile TiO2@C using a one-step self-combustion method without special equipment and complex process control. It was found that TiO2nanoparticles with various proportions of anatase to rutile were encapsulated in well-graphitized thin carbon shells. The photocatalytic activity of the prepared anatase/rutile TiO2@C samples was investigated as a function of the proportion of anatase to rutile. When the weight ratio of the anatase to rutile phase is83.8:16.2, the best photocatalytic activity can be obtained. After the solution was irradiated for30min, the degradation ratio of RhB was94%, which is comparable to that of commercial P25. Especially when the concentration of RhB was low, TiO2@C exhibited better photocatalytic activity than commercial P25TiO2.2. TiO2/γ-Fe2O3nanocomposites were successfully prepared by a facile solvothermal and thermal oxidation method. The proportion of TiO2to γ-Fe2O3can be tuned by simply changing the amount of reagents. The photocatalytic activity of the prepared TiO2/γ-Fe2O3samples was investigated as a function of the proportion of TiO2to γ-Fe2O3. It was found that a decrease in photocatalytic activity of TiO2can be caused by the combination of TiO2and γ-Fe2O3. However, when the weight ratio of γ-Fe2O3was lower than8%, TiO2/γ-Fe2O3exhibited a higher photocatalytic activity, which was comparable to that of commercial P25. Additionally, the magnetic property of TiO2/γ-Fe2O3enables the composite to be easily magnetically separated from the photocatalytic system by an external magnetic field, which facilitates the practical application of photocatalysts.3. Heterophase junction material of a-Fe2O3/γ-Fe2O3nanorods was successfully prepared by a facile thermal decomposition and redox method. Visible-light induced photodegradation of model dye RhB was investigated by using the as-prepared material as a photocatalyst. The formation of the heterophase junctions between α-Fe2O3and y-Fe2O3was found to remarkably enhance the visible-light photocatalytic activity of the nanocrystalline Fe2O3. a-Fe2O3/y-Fe2O3heterophase nanorods exhibit a higher visible-light photocatalytic activity,90%of RhB can be degraded after irradiation for12h, the rate is4.5times higher than that of α-Fe2O3and10times higher than that of γ-Fe2O3. The existence of y-Fe2O3enables the composite to be easily magnetically separated from the photocatalytic system. The recycling experiments show that80%of RhB can still be degraded at the fifth cycle, indicating that the a-Fe203/y-Fe2O3heterophase nanorods are quite stable during photocatalysis.