Synthesis And Mechanism Of Bismuth-Composite Photocatalyst

The environmental security problem caused by social development is increasingly becoming one of the biggest challenges in the world. In China, the environmental security problem has aroused great concern from the government and academia. For this, the State Environmental Protection Administration began to carry out the ?strategy of national environmental security? in 2003. Among them, water pollution is the greatest impact on human's life.Semiconductor photocatalysis, which can utilize the abundant solar energy for organic contaminants photodegradation, is of great significance to solve the environmental emergency. TiO2 has been one of the main most extensive research topics in semiconductor photocatalysis. However, semiconductors such as TiO2 cannot be widely applied because of their intrinsic large band gap and rapid recombination of the photon-generated carriers. For the practical application, it is the inevitable trend that exploiting efficient photocatalysts with visible light irradiation. In recent years, bismuth-containing semiconductors exhibit great potential applications in water splitting and degradation of organic pollutions under visible-light-response because of their low valence bands and high chemical stability, thus become more and more attractive.Based on these,in this work, we have improved the light absorption region and the separation of photon-generated carriers of bismuth-containing semiconductors?BiOX and Bi₂O₃? by crystal facet exposure, metal ions doping and compouding to promote visible-light-driven photocatalytic performance. The chemical co precipitation method, co precipitation and heat treatment, solution impregnation method are synthesis approach in our work. After detailed structure characterization, the samples were measured by degradation of RhB under visible-light irradiation. We have obtained the following conclusions.We have synthesized exposure of?110? crystal facet microspheres BiOX/PVP?x = Cl, Br, I? photocatalyst by co precipitation method under normal temperature and pressure with PVP. The formation mechanism?110? crystal facet was analyzed. Photocatalytic degradation of RhB experiments show that the BiOX/PVP shown high catalytic activity in the visible light and sunlight. Besides,they has good stability. The reason of photocatalytic activity increased are mainly?1? BiOX/PVP samples can adsorb more dye, at same time,the PVP molecules on the surface of sample accelerated electronic transfer,which is excited by indirect dye sensitization process so as to improve the photocatalytic activity;?2? exposure of the?110? crystal facet accelerated transfer of the hole,so reducing the photogenerated electron hole pairs of composite.Porous Bi₅O₇ I nanosheets were prepared by a facile thermal decomposition of BiOI nanosheets in air at 500? for 2 h. The porous Bi₅O₇ I nanosheets were mainly composed of irregular nanosheets with the layerthickness of 30-50 nm and the pore diameter distribution between 18-30 nm, it belonged to mesoporous mate-rial. The reason of porous formed is because the BiOI took of I2 during heat treatment.Compared with BiOI, the photocatalytic activity of porous Bi₅O₇ I nanosheets under visible light was appropriately 2 times than that of BiOI, and 2.3 times under simulated sunlight. The major reasons for the improvement in catalytic performance were the existence of multiple pores and the special band structure.With using BiOCl as main catalyst, the effect of compounding NiO was studied by using RhB as the target degradation.We found that 4% loading of composite photocatalyst has the best catalytic activity, improved 1.8 times compared with pure BiOCl. This is due to the p-type semiconductor NiO and p-type BiOCl formed P-P heterojunction, and improve the photocatalytic activity. Besides, through one step co precipitation method, we synthesized rare earth metal element dysprosium?Dy? doping BiOCl. The results showed that Dy3 + replace part of Bi3 + doping into BiOCl lattice, caused the changes of the band gap. The reason of its causes are mainly due to the special electronic shell structure of rare earth metal elements provide the 4f electron layer can reduce the width of band gap, so as to improve the photocatalytic activity.?-Bi₂O₃ was selected to composite different content of reduced graphene oxide?rGO?, the results showed that 1% of the rGO loading has the highest photocatalytic activity under visible light, which was 3 times than that of the pure ?-Bi₂O₃.Addition,the magnetic substrate SrFe₁₂O₁₉ were used to composite ?-Bi₂O₃ with different proportion by impregnation method. The influence of proportion of SrFe₁₂O₁₉ on photocatalytic activity was investigated. The ?-Bi₂O₃/SrFe₁₂O₁₉?15%? showed the highest photocatalytic activity. and then ?-Bi₂O₃/SrFe₁₂O₁₉?15%? was selected to composite rGO with different proportion using impregnation method too. In the end, 2% rGO/?-Bi₂O₃/ SrFe₁₂O₁₉ showed the highest photocatalytic activity. At same time,the repeated tests indicated that 2% rGO/?-Bi₂O₃/SrFe₁₂O₁₉ could be reused and the degradation rate of the same RhB solution could still reach to 90.2% after repeating 4 times. Graphene composite to improve the photocatalytic activity is mainly the result of three factors: the first is graphene introducing increased the sorption of dyes; the second is because graphene introduced for reducing the width of band gap, so that the sample can absorb more visible light; the third is because of the p-n junction formation of effective and graphene constitute a synergistic effect, accelerate the photogenerated electron hole separation.