Study On Modification And Photocatalytic Activity Of Complex Oxides Photocatalyst

As ecological environment problems and energy crisis arise, more and more governments and commercial establishments invest in green technology and clear energy. The industrial applications of Ti O2 promote the expansion of photocatalytic technology, which is so encouraging. The low quantum yield and the high recycling cost of photocatalysts are main reasons to slow down the industrialization of photocatalysts. Recently a large number of visible- light-driven photocatalysts with efficient catalytic ability have been exploited: Bi-based photocatalyst, Ag-based photocatalyst, polymer semiconductor photocatalyst, carbon-based photocatalyst and other metal oxide photocatalyst et al. To enhance the photodegradation performance, researchers have found several effective methods like semiconductor coupling, element doping, morphology controlling and dye sensitization et al.Here we focus on the modification of complex oxides（N i Fe2O4, BiFeO₃） photocatalyst by combining complex oxide with other semiconductor. Through a two-step route g-C₃N₄/NiFe₂O₄, Bi OBr-N i Fe2O4 and Bi O Br-BiFeO₃ composites（with different mass fraction） were fabricated and the photocatalytic capability was investigated by dye photodegradation（MB and Rh B）. The major research and significant conclusions are summarized as follows:1. g-C₃N₄ and NiFe₂O₄ were synthesized by calcination and solvothermal method respectively, which followed by a simple impregnation process. The crystalline, microstructure, magnetism and optical property of g-C₃N₄/NiFe₂O₄ composites were analyzed by XRD, TEM, VSM and DRS tests. The TEM pictures of catalysts indicated that N i Fe2O4 nanoparticles and nanosheets were decorated on g-C₃N₄ sheet, which could get better photocatalysts distribution; in XPS analysis the chemical shift of N element implied the existence of heterojunction structure between g-C₃N₄ and N i Fe2O4. The photodegradation rate of MB over g-C₃N₄/NiFe₂O₄ composites photocatalysts followed zero-order reaction model and 7.5% g-C₃N₄/NiFe₂O₄ exhibited the best photocatalytic activity, which indicated that the heterostructure could decrease the recombination of charges for higher photo-Fenton activity. During five runs of photodegradation exper iments g-C₃N₄/NiFe₂O₄ composite photocatalyst could keep high photocatalytic activity, indicating that the prepared composite photocatalyst had excellent photocatalytic stability and magnetic recovery property.2. Bi OBr-NiFe₂O₄ composite photocatalyst was prepared by a reliable impregnation strategy and the catalysts were researched by FT-IR, XRD, TEM, VSM, DRS and XPS tests. The XRD and XPS tests indicated that there were no other impurities in catalysts; the VSM showed that Bi O Br-N i Fe2O4 composite photocatalyst had high saturation magnetization. As the Bi O Br content increased, the adsorption ability and degradation efficiency rose; more importantly when the mass fraction of Bi OBr exceeded more than 25%, the reaction rate was disturbed and the R2 decreased. From the recycling tests, the phenomenon of C/C0 fluctuation implied that the excess adsorption of dye could affect the Rh B recycling photodegradation. In addition, a reasonable mechanism was proposed according to the experiment results.3. Bi OBr-BiFeO₃ composite photocatalyst was synthesized via a solvothermal method and the crystal system, optical absorption, morphology and profile were analyzed by XRD, DRS, TEM and SEM tests. The SEM pictures showed that the introduction of Bi OBr decreased the aggregation of BiFeO₃ nanoparticles and enlarged the specific surface area of catalysts. The photodecomposition of Rh B under visible light irradiation was utilized to evaluate the photocatalytic performance of the as-prepared photocatalysts, which confirmed that 20% Bi O Br-BiFeO₃ and 35% Bi OBr-BiFeO₃ composite had higher photocatalytic activity than pure Bi O Br and BiFeO₃. It could be induced that the heterojunction of composite accelerated the separation of photo-generated carriages. Photo- induced holes were demonstrated the main oxidants during the Rh B photodecomposition system. On the basis of experiment a reasonable reaction mechanism was referenced to explain the charge separation in the heterojunction interface.