Preparation Of Hematite-based Composite Photocatalysts And Study Of Their Performance In Degradation Of Toluene

Currently with increasing environmental pollution, the management of volatile organic compounds (VOCs) in the air is a top priority. A most common and typical example of VOCs is toluene. Photocatalytic technology based on the utilization of solar energy has demonstrated a very important prospect in the application of controlling toluene and other VOCs. So the development of photocatalytic system with high quantum efficiency based on solar energy utilization has become an important research topic. On this basis, α-Fe2O3was used as a base material to construct α-Fe2O3/GO, Ag/α-Fe2O3and g-C3N4/α-Fe2O3complex systems. In situ infrared spectroscopy was applied to study the photocatalytic degradation process of toluene over these materials under visible light. Light-induced charge migration and photocatalytic degradation mechanisms were explored in the constructed photocatalytic systems. The main results obtained are as follows:(1) Successful synthesis of the hollow spindle-shaped α-Fe2O3catalyst of high purity as well as good crystallinity. Through the DRS, BET characterization on the samples and detailed analysis of SPV mechanisms, enhanced visible-light absorptive capacity and adsorption capacity as well as effective separation capability of photogenerated carriers were found due to the hollow structure of the sample.(2) Ag/α-Fe2O3composite systems were prepared by impregnation of loading precious metal silver. Photocatalytic activity and the effects of different Ag loadings on toluene degradation rates over Ag/α-Fe2O3under visible light were investigated using in situ infrared spectroscopy. The results showed that during the xenon lamp irradiation for6h, the photocatalytic activity of toluene over this complex was higher than that over commercial α-Fe2O3and hollow spindle-shaped α-Fe2O3. Furthermore, complete degradation of toluene into degradation products of CO2and water could be achieved and the degradation rate reached88%over this composite. The enhanced photocatalytic activity after loading Ag catalyst was mainly attributed to Ag and α-Fe203composite system improves the light-induced charge separation efficiency. We also found that Ag loadings had some influence on the degradation rate by Ag/α-Fe2O3to a certain extent. When Ag loading was about1.0wt%, Ag/α-Fe2O3had a highest degradation rate of88%.(3) Preparation of a composite system of α-Fe2O3and graphene based new carbon material α-Fe2O3/GO. The complex system has a stronger ability than a single α-Fe2O3in absorbing visible light, enhanced photo-induced carriers separation and stronger surface adsorption capabilities. The photocatalytic toluene degradation rate of80%could be achieved in6h using the composite catalyst compared with a single α-Fe2O3. By using in situ infrared spectroscopy for the detection of the reaction products, benzaldehyde, benzoic acid, CO2and water were identified. Increased degradation rate was mainly due to the superior adsorption characteristics of graphene, and the introduction of GO caused a shift of the conduction band of α-Fe2O3in the composite system towards the negative direction, thereby speeding up the effective separation of photo-generated carriers and improving the quantum efficiency.(4) Using a simple solvothermal method, we successfully loaded the α-Fe2O3nanoparticles onto g-C3N4to form a composite photocatalytic system g-C3N4/α-Fe2O3. The products over the composite system during the photocatalytic degradation of toluene were benzaldehyde, benzoic acid, CO2and water. The toluene degradation rate of91%in6h. Its high photocatalytic performance is mainly due to the synergistic effect between α-Fe2O3and g-C3N4and a large specific surface area of the complex structure. Meanwhile, the mass ratio of the components in the composite system also affect the photocatalytic activity. The results showed when the component g-C3N4content was70wt%, g-CjN4/a-Fe2O3composite system exhibited a highest photocatalytic activity and had a certain stability since the catalytic activity remained unchanged after repeated use for times.(5) By comoparison, the performance order of α-Fe2O3based composite materials for the photocatalytic degradation of toluene under visible light is g-C3N4/a-Fe2O3composite> Ag/a-Fe2O3composite> a-Fe2O3/GO composite>hollow spindle-shaped α-Fe2O3.