Study On Preparation,Characterization And Photocatalytic Activity Of Pyrochlore(Sr_0.6Bi_0.305)₂Bi₂O₇ Composite System

Now the control and treatment of environmental pollution is an impending demand ofhuman society since the environmental pollution has become a vital threat to the health of people.Among many methods for governing environment,semiconducting photocatalysis which can drive the redox reaction via directly utilizing solar energy to achieve the purification of environmental pollution is a environment-friendly technology and has acttracted extensive attention.(Sr_0.6Bi_0.305)₂Bi₂O₇ with the pyrochlore-type structure is an especial compound containing mixed valent states of Bi(Bi³⁺and Bi⁵⁺).In our recent study,we have found that the energy band gap?E_g?of(Sr_0.6Bi_0.305)₂Bi₂O₇ is rather small and about in the range of 1.25?1.35 e V.The photocatalytic efficiency of pure(Sr_0.6Bi_0.305)₂Bi₂O₇ is a little low because the recombination of photogenerated electrons and pairs occurs easily,although it has a wide range of optical absorption.Considering the distinct defect of(Sr_0.6Bi_0.305)₂Bi₂O₇,the semiconductors with larger E_g like SrCO₃,Cd S,and Zn O are used to construct the heterostructured photocatalysts to improve the corresponding photocatalytic activity.The major research contents are listed as follows:?1?(Sr_0.6Bi_0.305)₂Bi₂O₇/SrCO₃ composite photocatalyst was prepared by the one-step hydrothermal method and further characterized by XRD,SEM,TEM and UV-Vis DRS.The photocatalytic reduction of Cr?VI?and degradation of rhodamine B?Rh B?were tested.The measured results showed that the photocatalytic activity of the(Sr_0.6Bi_0.305)₂Bi₂O₇/SrCO₃ composites was significantly improved in comparison with that of the pure(Sr_0.6Bi_0.305)₂Bi₂O₇and SrCO₃.After 35 minutes of light irradiation,about94%of Cr?VI?solution adding(Sr_0.6Bi_0.305)₂Bi₂O₇/SrCO₃?2:1?composite catalyst was reduced.The composite photocatalyst can improve the utilization rate of visible light and enhancethe separation efficiency of photogenerated carriers and the photocatalytic activity.?2?The one-step hydrothermal method was used to prepare(Sr_0.6Bi_0.305)₂Bi₂O₇/ZnO heterostructured photocatalyst.XRD,SEM,TEM,XPS and UV-Vis DRS were further carried out to characterize the crystal structure,micromorphology,chemical valence state,chemical valence,and optical properties of the samples.The photocatalytic activity was evaluated by the degradation of methylene blue?MB?solution.The results showed that20 wt%(Sr_0.6Bi_0.305)₂Bi₂O₇/Zn O had the best photocatalytic activity.After 150 minutes of irradiation,about 98%of MB solution was degraded and the composite catalyst exhibited very high stability.?3?(Sr_0.6Bi_0.305)₂Bi₂O₇/Cd S composite photocatalyst was synthesized by ultrasound-assisted chemical precipitation.The crystal structure,microstructure,chemical valence state and optical properties of the prepared samples were characterized by means of XRD,SEM,TEM,XPS and UV-Vis DRS.The photocatalytic activity of the sample was evaluated by photocatalytic hydrogen generation.The results showed that0.05 wt%(Sr_0.6Bi_0.305)₂Bi₂O₇/Cd S had the best photocatalytic activity.After 5 hours of visible light irradiation,H₂ yield of Cd S was 1200?mol/g and that of 0.05 wt%(Sr_0.6Bi_0.305)₂Bi₂O₇/Cd S was about 7800?mol/g.The H₂ output of 0.05 wt%(Sr_0.6Bi_0.305)₂Bi₂O₇/Cd S was 6.5 times as high as that of pure Cd S.(Sr_0.6Bi_0.305)₂Bi₂O₇/Cd S heterojunction with the matching energy band and tight coupling interface reduced the energy loss in the migration process,thus achieved the rapid separation of photogenerated electron-hole pairs and effective inhabitation of the recombination of photogenerated carriers,and improved the photocatalytic efficiency.