Application Research Of Visible-light-driven BiOBr Photocatalyst For Simulant Dye Wastewater Treatment

The treatment of dye wastewater has been a big challenge in the field of industrial wastewater treatment for chemical complexity, high chromaticity and poor biodegradability. Therefore, it is necessary to develope economic and efficient technologies to treat dye wastewater. In the recent years, visible-light photocatalysis attracted a wide attention for its outstanding performance including low energy, high reaction rate, nontoxicity, non-selectivity and complete degradation.BiOBr is a novel semiconductor visible-light-driven photocatalyst with open crystal structure and indirect transition mode which contribute to the separation of electrons and holes. Among the preparation methods of BiOBr, hydrothermal is widely studied because of its simple controllable synthesis process. However, the catalyst synthesis by hydrothermal is mostly made up of organic materials with low catalytic efficiency. Therefore, developing the highly active BiOBr catalyst prepared by simple raw material is an important subject. Furthermore, single BiOBr has the defect of high electron-hole recombination efficiency, so it is important to modify BiOBr with different methods to promote photocarrier separation efficiency and improve its photocatalytic performance.In this paper, high catalytic activity BiOBr was prepared by hydrothermal utilizing inorganic materials:Bi(NO3)3·5H2O, NaBr, HNO3. The optimized BiOBr catalyst was selected when in contrast to the reported organic materials made catalyst. Taking Rhodamine B as the target pollutant, visible light catalytic activity of catalyst was investigated, and the stability of catalyst was studied. Furthermore, the active species and mechanism in the process of photocatalytic reaction was discussed. In addition, different mass ratio of C3N4/BiOBr and BiOI/BiOBr composite catalysts were prepared utilizing Semiconductor compound modification technology. The photocatalytic performance of composite catalysts were studied and photocatalytic mechanism was explored. Main results were as follows:1?Preparation and performance study of BiOBr photocatalyst. BiOBr photocatalyst was prepared utilizing inorganic materials:Bi(NO3)3·5H2O, NaBr, HNO3. The experimental results of Rhodamine B's degradation showed that, the catalytic activity of the prepared BiOBr was much higher than the control group and the reaction rate increased by 170%. It was mainly attributed to the unique flower piece layer structure, the smaller particle size and large specific surface area of BiOBr photocatalyst. The experimental results also showed that BiOBr photocatalyst still remained high catalytic activity after reused many times. The free radicals capture experiment and ESR measurement showed that, h+ and ·O2- were the main active species in the process of Rhodamine B's degradation by BiOBr photocatalyst.2. Preparation and performance study of C3N4/BiOBr composite photocatalyst. PL and transient photocurrent testing results showed that, fluorescence emission peak intensity of C3N4/BiOBr was weaker than BiOBr, while photocurrent value was bigger than BiOBr, which indicated the lower electron-hole recombination efficiency. The experimental results of Rhodamine B's degradation showed that,15wt% C3N4/BiOBr composite photocatalyst had the optimized photocatalytic activity. Its reaction rate increased by 180% and the degradation time reduced by 60% compared with BiOBr photocatalyst. Therefore, compositing C3N4 on BiOBr photocatalyst could effectively lower the electron-hole recombination efficiency and significantly improve the photocatalytic activity of BiOBr photocatalyst. This was due to the heterojunction formed between C3N4 and BiOBr, in where electrons migrated from the conduction band of C3N4(-1.12eV) to the conduction band of BiOBr(0.31eV) while the holes migrated from the valence band of BiOBr(3.06eV) to the valence band of C3N4(1.59eV), which effectively inhibited the recombination of electrons and holes.3?Preparation and performance study of BiOI/BiOBr composite photocatalyst. PL and transient photocurrent testing results showed that, fluorescence emission peak intensity of BiOI/BiOBr was weaker than BiOBr, while photocurrent value was bigger than BiOBr, which indicated the lower electron-hole recombination efficiency. The experimental results of Rhodamine B's degradation showed that,8wt% BiOI/BiOBr composite photocatalyst had the optimized photocatalytic activity. Its reaction rate increased by 91% and the degradation time reduced by 53% compared with BiOBr photocatalyst. Therefore, compositing BiOI on BiOBr photocatalyst could effectively lower the electron-hole recombination efficiency and significantly improve the photocatalytic activity of BiOBr photocatalyst. This was due to the heterojunction formed between BiOI and BiOBr. Under visible light irradiation (X>420nm), the electrons could be migrated from the valence band top to higher conduction band positions. Subsequently, electrons migrated from the conduction band of BiOI(-0.64eV) to the conduction band of BiOBr(0.11eV) while the holes migrated from the valence band of BiOBr(3.06eV) to the valence band of BiOI(2.31eV), which effectively inhibited the recombination of electrons and holes.