Fabrication And Photocatalytic Properties Of BiOBr_xI_1-x Solid Solution Composite Nanofibers

Photocatalysis has been considered one of the potential ways to solve environmental pollution problems.The development of new semiconductor photocatalytic materials has become a trend in photocatalysis.Bismuth oxyhalide(Bi OX,X=Cl,Br,I)has become a promising material in recent ten years because of its unique layered structure and indirect bandgap,which reduces the probability of photogenerated carrier recombination and shows excellent photocatalytic activity.Due to its narrower band gap,Bi OI has a higher light energy utilization rate than Bi OCl and BiOBr.Still,the corresponding potential of Bi OI has limited redox ability and lower photocatalytic activity.BiOBr_xI_1-x or Bi OCl_xI_1-x solid solution can achieve a broad spectrum response and obtain higher redox ability because its energy band structure can be adjusted by halogen substitution.However,like other photocatalysts,the photogenerated electrons and holes in single-component BiOBr_xI_1-x or Bi OCl_xI_1-x solid solution are easily recombined due to its limited space carrier migration,so its photocatalytic activity needs to be improved.Therefore,it is an effective way to enhance the photocatalytic activity by constructing a heterostructure system of BiOBr_xI_1-x or Bi OCl_xI_1-x solid solution and semiconductor or carbon materials using the built-in electric field to promote the effective separation of photogenerated carriers and reduce the recombination probability.On the other hand,if BiOBr_xI_1-x or Bi OCl_xI_1-x solid solution and the constructed heterostructure are prepared into nanomaterials,their specific surface area is large,conducive to improving their photocatalytic activity.However,nanopowder is easy to agglomerate and reduce the specific surface area in liquid phase photocatalysis due to its high surface energy,thus reducing its photocatalytic activity.At the same time,small-sized nanopowder is challenging to settle after reaction,which is not conducive to separation and reuse.To solve the above problems,taking BiOBr_xI_1-x solid solution as the primary research object,a series of heterojunction nanofibrous materials,including BiOBr_xI_1-x@TiO₂,BiOBr_xI_1-x@Fe₂TiO₅ and BiOBr_xI_1-x@CNFs,were designed and prepared by electrospinning,solvothermal,and charge induced in-situ precipitation methods.The built-in electric field at the heterojunction interface improved the charge separation and transfer efficiency.Nanofiber materials'high specific surface area can increase the reaction active sites and enhance photocatalytic activity.Its super long one-dimensional structure and unique three-dimensional nanomesh felt structure are conducive to solving the agglomeration of small-sized nanomaterials and improving the separability and reusability of materials.The specific research contents are as follows:(1)Using Titanium dioxide(TiO₂)nanofibers as templates,BiOBr_xI_1-x@TiO₂heterojunction nanofibers were prepared by a solvothermal method.The results show that the continuous adjustment of the band structure of the solid solution is realized,the solid solution with the balance of light absorption and redox capacity is recognized,and higher photocatalytic activity is obtained by changing the ratio of Br and I elements in the solid solution.Meanwhile,the BiOBr_xI_1-x@TiO₂ heterojunction nanofibers are a p-n heterostructures with type II contact,which could effectively reduce the recombination of photogenerated charge and enhance the photogenerated charge separation.The experimental study on photocatalytic Methyl orange(MO)degradation shows that the photocatalytic activities of BiOBr_xI_1-x@TiO₂ heterojunction nanofibers were significantly higher than those of pure TiO₂ nanofibers and BiOBr_xI_1-x nanoflowers.The most increased photocatalytic degradation of BiOBr_xI_1-x@TiO₂ heterojunction nanofibers was 51.6 times higher than TiO₂nanofibers and 2.1 times higher than those of BiOBr_xI_1-x solid solution nanoflowers,respectively.In addition,its super long one-dimensional mesh structure makes it have good separation,recovery,and recycling performance after liquid phase reaction.(2)Using narrow bandgap Iron titanate(Fe₂TiO₅)electrospun nanofibers as templates,BiOBr_xI_1-x@Fe₂TiO₅ heterojunction nanofibers were prepared by solvothermal method.The results show that BiOBr_xI_1-x@Fe₂TiO₅ heterojunction nanofibers with Fe₂TiO₅ as the carrier have better properties than BiOBr_xI_1-x@TiO₂ heterojunction nanofibers have wider solar spectral utilization.The energy band structure with broad spectral absorption and balance of redox ability improves the photocatalytic performance of heterojunction nanofibers.The BiOBr_xI_1-x@Fe₂TiO₅ heterojunction interface is a Z-type heterojunction band structure conducive to separating photogenerated carriers.At the same time,by adjusting the energy band structure of solid solution in heterojunction,composites with broad spectral absorption and excellent redox ability were obtained,which showed excellent photocatalytic properties.The photocatalytic degradation experiments of MO showed that the reaction rate of BiOBr_xI_1-x@Fe₂TiO₅ heterojunction is 12.0 times higher than those of Fe₂TiO₅ nanofibers and2.8 times than those of BiOBr_xI_1-x solid solution nanoflowers.In addition,the BiOBr_xI_1-x@Fe₂TiO₅ heterojunction nanofibers have magnetic separation characteristics,which can be easily separated and recovered under the action of the external magnetic field.(3)Using electrospun Carbon nanofibers(CNFs)as templates,BiOBr_xI_1-x@CNFs heterojunction nanofibers were prepared using a solvothermal method.The results show that heterojunctions can be formed between semiconductors and carbon materials.Due to carbon materials'low resistivity and high charge transferability,the BiOBr_xI_1-x@CNFs heterojunction realizes the effective separation of photogenerated carriers.The experimental study of photocatalytic degradation of MO showed that BiOBr_xI_1-x@CNFs heterojunction nanofibers also exhibit solid solution component dependent photocatalytic activity,which is significantly higher than that of single-component BiOBr_xI_1-x solid solution nanoflowers.The highest reaction rate for MO degradation is 1.6 times higher than those of BiOBr_xI_1-x solid solution nanoflowers,which indicates that the one-dimensional structure of CNFs is conducive to the carrier transfer and transport to improve the photocatalytic activity.In addition,the three-dimensional mesh structure of BiOBr_xI_1-x@CNFs heterojunction nanofibers makes them have good separation,recovery,and recycling performance after liquid phase reaction.(4)Using electrospun PAN/PVP/Bi³⁺nanofibers as precursors,BiOBr_xI_1-x@PAN flexible composite nanofibers were prepared by charge induced in-situ precipitation.The results show that organic nanofibers avoid the fragility of inorganic nanofibers,making the composite nanofibers have an excellent flexible,self-supporting,and porous structure.The uniform dispersion and loading of BiOBr_xI_1-x solid solution on the surface of PAN porous nanofibers provides rich reaction active sites for surface reaction and provides an excellent mass transfer channel for the adsorption and diffusion of reactants,which is conducive to improving the photocatalytic activity.The highest reaction rate of photocatalytic degradation of MO is 5.6times that of BiOBr_xI_1-x nanopowders.In addition,the unique macro felt,and flexible self-supporting structure of BiOBr_xI_1-x@PAN composite nanofibers can realize self-suspension liquid phase photocatalysis,showing excellent separation,recovery,and reuse performance.