Preparation Of BiFeO₃ Nanofiber Composite By Electrospinning And Its Photocatalytic Activity

As the rapid development of modernization in recent years,excessive industrial wastewater is discharged,which leads to serious pollution to the water environment.Some harmful microorganisms and organic antibiotics existing in the rivers and lakes can be recalcitrant pollutant.It poses a serious threat to the ecological environment as well as the ecosystem.The photocatalytic redox method is widely studied for degrading pollutant as its low cost and environment-friendly degradation efficiency.Generally,researchers prefer photocatalysts which are excellent chemically stable and can obtain easily with high activity as well as high sunlight utilization rate.As a result,the new bismuth-based photocatalytic material bismuth ferrite（BiFeO₃）attracts their attention.BiFeO₃ has narrow forbidden band width（～ 2.2e V）,which enables it to respond to visible light effectively and can keep its chemical stability.It is also a multifunctional material with ferromagnetic and ferroelectricity at room temperature,which has good applications prospects.However,single-phase BiFeO₃ has shortcomings such as low quantum efficiency and poor light absorption capacity,so it is necessary to find a modification method to improve its photocatalytic performance.This paper bases on electrospinning technology to prepare the one-dimensional BiFeO₃ nanofibers,while the BiFeO₃ nanofibers is modified to promote their photocatalytic performance.Combined with different preparation methods,the fibrous BiFeO₃-based composite nanofibers are designed,and all of them can be responded to visible light.In this paper,we successfully prepared purephase BiFeO₃ nanofibers by electrospinning technology,and the effect of polymer concentration,spinning voltage and different annealing temperatures on fiber phase and morphology are expored.Then the MOFs nanoparticles and the cadmium sulfide（CdS）nanosheets are loaded on BiFeO₃ nanofibers by ultrasonic crystallization method and hydrothermal growth method.Moreover,the photocatalysis mechanism and photocatalytic degradation performance of composite nanofibers are further discussed.The main research contents are as follows :（1）The effect of electrospinning process parameters on the BiFeO₃ nanofibers phase morphology is studied.the Polyvinylpyrrolidone（PVP）is introduced into the inorganic iron bismuth solution to form spinning precursor solution.BiFeO₃-PVP composite nanofibers are obtained by electrostatic spinning.The muffle furnace is used to anneal to remove organic matter in primary nanofibers,which can form a pure inorganic phase BiFeO₃ nanofibers.The effects of different annealing temperatures,different PVP concentrations and different spinning voltages on the phase morphology of BiFeO₃ nanfibers are further investigated.It is found that when the annealing temperature is higher than 500 ℃,the PVP concentration is about 8wt%-10wt%,and the spinning voltage is about 13 k V,the phase and morphology of the obtained BiFeO₃ nanofibers are the most excellent.The samples are characterized by scanning electron microscope and X-ray diffractometer.The test results have shown that under these process parameters the BiFeO₃ nanofibers are successfully synthesized,and BiFeO₃ nanofibers showed good thermal stability and photocatalytic performance.（2）Preparation of BiFeO₃/ZIF-8 composite nanofiber material by ultrasonic crystallization,and its photocatalytic performance is investigated.A new BiFeO₃/ZIF-8 composite nanofiber is successfully prepared by loading ZIF-8 nanoparticles onto the BiFeO₃ nanofibers surface,which is combined electrospinning technology with ultrasonic crystallization method.The influence of different ZIF-8 loading ratios on the photocatalytic performance is investigated.The test showed that the adsorption capacity and photocatalytic activity of the composite photocatalyst are significantly improved.The designed hybrid composite nanostructure promotes the separation of photogenerated carrier charge,which reduces the recombination rate of photogenerated electron holes and improves its adsorption performance under the action of the cocatalyst ZIF-8.In addition,the resulting BiFeO₃/ZIF-8 photocatalyst also exhibits high surface area,which helps to expose more active sites during photocatalysis and increases the adsorption capacity to the target reactants.The test of degrading methylene blue（MB）under visible light show that the degradation efficiency of BiFeO₃/ZIF-8 composite photocatalyst is improved by about 52%,it reached to 83.7%.（3）Solvothermal preparation of BiFeO₃/CdS composite material and its photocatalytic performance is investigated.A series of BiFeO₃/CdS composite nanofiber with different CdS loading capacity is synthesized by electrospinning technology and hydrothermal method.The SEM representation reveals that the prepared composite nanofiber has a uniform morphology with clear fibrous structure.It can be found that the CdS nanosheets are closely attached to the surface of BiFeO₃ nanofibers.The influence of different CdS nanosheets loading capacity on BiFeO₃ is systematically investigated,which may have influence on the morphology structure and photocatalytic degradation performance.After a series of characterization analyze,it can be seen that the absorption band of samples are shifted to infrared light,and its visible light absorption is enhanced.In addition,the width of the forbidden band and the PL fluorescence intensity are significantly weakened,which promotes the separation of photogenerated carriers.The CdS nanosheets used the nanofibers surface as growth fulcrums during hydrothermal process.The flake-shaped CdS is successfully grew on BiFeO₃ nanofibers.Moreover,the introduction of CdS does not change the phase of BiFeO₃,it proves that these two materials successfully compounded.Among them,the BCdS-2 composite nanofiber exhibits excellent visible light response,and its band gap is about 1.78 e V.Compared with the original BiFeO₃,the photocatalytic performance of the BCdS-2 sample is improved to 98%,and the photocatalytic cycle stability is better.After four cycles of degradation,the degradation rate is only reduced by about 2.8%.The reactive free radicals generated in the photocatalytic process are studied by trapping experiments.The results displays that the main active species involved in the photocatalytic process is hydroxyl radical（·OH）,followed by holes（h⁺）.