Controllable Preparation And Photocatalytic Properties Of Bismuth-based Oxide Heterojunction Nanofibers

With the progress of science and technology,the rapid development of modern industry significantly improved people's living standards,but also brought increasingly serious energy shortage and environmental pollution problems.Semiconductor photocatalysis technology,as an environmentally friendly green technology,can directly convert abundant solar energy into chemical energy,which is an effective way to solve the problem of energy shortage and environmental pollution.Bismuth-based oxide semiconductors,which have wide visible light response range and good physical and chemical stability,have become the forefront and hotspot in the field of photocatalytic materials.However,they still face the following problems in the application of photocatalysis:First,the photogenerated electrons and holes in single-component materials are easy to be recombined,resulting in low yield of light quantum and weak photocatalytic activity.Second,nano-sized photocatalysts are conducive to surface photocatalytic reaction,but it is easy to agglomerate in use due to their high surface energy,which could reduce the exposure of reaction sites and decrease the photocatalytic activity.In order to solve the above problems,a series of Bi Fe O₃ based bismuth-based oxide semiconductor heterojunction nanofibers materials were designed and prepared by the combination of electrospinning and solvothermal methods.The built-in electric field at the interface of the heterojunction was used to improve the charge separation efficiency,and the one-dimensional characteristics of nanofibers were used to enhance the charge transport and transfer.The nano-sized diameter and three-dimensional network mat structure not only maintains a high specific surface area,but also overcomes the problem of agglomeration.At the same time,the ferromagnetism of Bi Fe O₃ also improves the separation and recycling ability of the materials.The specific research contents are as follows:?1?The electrospinning preparation and photocatalytic properties of Bi Fe O3 and Bi Fe O₃/Bi₂₅Fe O₄₀ heterojunction nanofibers.One-dimensional Bi Fe O₃ nanofibers were prepared by the combination of electrospinning technique and calcination method.In addition,Bi Fe O₃/Bi₂₅Fe O₄₀ heterojunction nanofibers with different component ratios were obtained by adjusting the ratio of Bi?NO3?3·5H2O and Fe?NO₃?₃·9H₂O in precursor solution.The results show that Bi Fe O₃ nanofibers have higher photocatalytic activity than Bi Fe O₃ nanoparticles.The reaction rate of Bi Fe O₃ nanofibers for oxygen evolution is 1.35 times higher than that of Bi Fe O₃nanoparticles,which indicates that the one-dimensional structure of nanofibers is beneficial to charge transport.On the other hand,the photocatalytic activities of Bi Fe O₃/Bi₂₅Fe O₄₀ nanofibers were significantly higher than those of pure Bi Fe O₃and Bi25Fe O40 nanofibers.The highest photocatalytic Rh B degradation and oxygen evolution rate of Bi Fe O3/Bi25Fe O40 heterojunction were 48.4 times and 2.4 times higher than those of Bi Fe O₃ nanofibers,and 11.9 times and 6.5 times higher than those of Bi₂₅Fe O₄₀ nanofibers,respectively.In addition,the Bi Fe O₃ and Bi Fe O3/Bi25Fe O40 heterojunction nanofibers have magnetic separation characteristics,which can be easily separated and recovered under the external magnetic field.?2?The controllable preparation and photocatalytic property of Bi Fe O3/Bi2Mo O6 and Bi Fe O3/Bi2WO6 heterojunction nanofibers.Using Bi Fe O3nanofibers as templates,Bi Fe O3/Bi2Mo O6 and Bi Fe O3/Bi2WO6 heterojunction nanofibers were prepared by solvothermal method.By adjusting the concentration of solvothermal precursor solution,the loading contents of Bi₂Mo O₆ and Bi₂WO₆nanosheets can be adjusted,and the discrete Bi2WO6 nanosheets/Bi Fe O3 nanofibers heterojunction can be obtained by optimizing the reaction conditions.The results show that the Bi Fe O3/Bi2Mo O6 heterojunction interface is a Z-type heterojunction band structure,while the Bi Fe O₃/Bi₂WO₆ heterojunction interface is a II-type heterojunction contact.Both could effectively reduce the recombination of photogenerated charge.The experimental study on photocatalytic Rh B degradation shows that the highest reaction rate of Bi Fe O₃/Bi₂Mo O₆ heterojunction is 55.2 times higher than that of Bi Fe O₃ nanofibers,and 7.0 times higher than that of Bi₂Mo O₆nanosheets;the highest reaction rate of Bi Fe O3/Bi2WO6 heterojunction is 36.7 times higher than that of Bi Fe O3 nanofibers,and 8.7 times higher than that of Bi2Mo O6nanosheets.Compared with II-type heterojunction,the photogenerated electrons and holes in Z-type heterojunction have stronger redox ability,so Bi Fe O₃/Bi₂Mo O₆heterojunction has higher photocatalytic activity than Bi Fe O3/Bi2WO6heterojunction.In addition,the study of Bi Fe O3/Bi2WO6 heterojunction nanofibers shows that the construction of Bi Fe O₃/Bi₂WO₆ heterojunction nanofibers with discrete structure can not only achieve effective charge separation but also realize the spatial separation of redox reaction sites.And,the photocatalytic activity of discrete Bi Fe O₃/Bi₂WO₆ heterojunction nanofibers is higher than that of core-shell heterojunction nanofibers.?3?The controllable preparation and photocatalytic properties of Bi Fe O₃/Bi OCl and Bi Fe O3/Bi OBr heterojunction nanofibers.Using Bi Fe O3 nanofibers as templates,Bi Fe O₃/Bi OCl and Bi Fe O₃/Bi OBr heterojunction nanofibers with different loading amount of bismuth oxyhalide were prepared through solvothermal method by adjusting the solvothermal reaction conditions.The bismuth oxyhalide nanosheets grown vertically on the surface of Bi Fe O3 nanofibers,forming an one-dimensional multi-stage composite structure,which is conducive to surface photocatalytic reaction.The results show that Bi Fe O₃/Bi OCl and Bi Fe O₃/Bi OBr heterojunction nanofibers can effectively separate photogenerated charge.The highest reaction rates for nitrogen fixation and Rh B degradation of Bi Fe O3/Bi OCl heterojunction nanofibers are 22.0 times and 69.3 times higher than those of Bi Fe O₃ nanofibers,and5.2 times and 5.6 times higher than those of Bi OCl nanosheets;the highest reaction rates for nitrogen fixation and Rh B degradation of Bi Fe O3/Bi OBr heterojunction nanofibers are 29.0 times and 72.8 times higher than those of Bi Fe O3 nanofibers,and5.0 times and 12.5 times higher than those of Bi OBr nanosheets,respectively.The difference of Fermi level between the two components in Bi Fe O₃/Bi OBr heterojunction is larger than that in Bi Fe O3/Bi OCl,resulting in a stronger built-in electric field and more efficient charge separation.Therefore,the photocatalytic activities of Bi Fe O3/Bi OBr heterojunction are higher than those of Bi Fe O3/Bi OCl.Bi Fe O₃/Bi OCl and Bi Fe O₃/Bi OBr nanofibers possessing ferromagnetism have good separation and recycling ability after liquid reaction.