Exploration On Preparation And Photoelectric Properties Of Bismuth Ferrate Polycrystalline Fibers

To solve water pollution problems,highly efficient visible light photocatalysts have received much attention in recent years,providing a non-toxic and effective way to treat wastewater by decomposing various organic compounds using clean solar energy.Among many photocatalysts,bismuth-based semiconductor oxides have a special Aurivillius layered structure,which reduces the symmetry of the structure and also gives them high oxidation activity and charge mobility when used as photocatalytic materials,showing excellent performance in visible light photocatalytic reactions.BiFeO3(BFO),as a member of bismuth-based semiconductor oxides,has good visible light absorption(Eg≈2.2 eV),excellent photoelectric properties and good chemical stability,while BFO is the only multiferroic material that maintains ferroelectricity and ferromagnetism at room temperature and has promising applications.However,the photocatalytic activity of BFO is still limited by the low quantum yield caused by the high complexation of photogenerated electron-hole pairs.Therefore,the visible photocatalytic performance of BFO is improved by modifying BFO thereby.In this thesis,BFO fibers were prepared by sol-gel method combined with electrostatic spinning process,and single-phase hollow BFO(SPH-BFO)fibers were prepared by preferentially selecting precursor sols,using Fe(NO3)3.9H2O and Bi2O3 as Fe source and Bi source,respectively,ethylene glycol methyl ether as solvent,and citric acid as ligand.On this basis,the goal was to optimally enhance the photocatalytic performance of BFO fibers through controlling the heat treatment temperature for morphology and crystalline phase modulation,doping modification and construction of heterojunctions to regulate the electronic structure of BFO and suppress the complexation of electron-hole pairs,thus improving the photocatalytic performance of BFO fibers.The main findings of this paper are as follows:(1)The optimal raw materials and ratios were firstly selected by optimizing the iron source,bismuth source and ligand,taking into account the spinning properties of the reaction solution and the mechanical and physical aspects of the fibers.The experiments showed that the citric acid system(BFO-3)fiber has the best quality.The BFO-3 fiber starts to crystallize at 450℃,and the crystallinity increases with the increase of heat treatment temperature,and the second phase Bi2Fe4O9 appears in the fiber when the heat treatment temperature increases to 600℃,and the second phase content increases when the temperature continues to increase.By comparing the specific surface area of BFO-3 fibers at different heat treatment temperatures,it was found that BFO-3-550℃(SPH-BFO)fibers have the best specific surface area,which is related to the hollow structure of SPH-BFO fibers.SPH-BFO fibers have the lowest fluorescence emission peaks,indicating that well-crystallized hollow nanofibers can greatly hinder the photoexcited carrier compounding,with efficient interfacial charge transfer and higher carrier separation efficiency,optimal photocatalytic performance,and superoxide radicals and holes as the main reactive groups involved in the degradation of RhB.(2)The introduction of Gd element caused the phase change of BFO structure,and the BFO structure changed from rhombic phase to orthorhombic phase,with the increase of Gd content,the orthorhombic phase content increased,neither impurity peaks nor secondary phase peaks were found,and the fiber still exhibited a hollow structure.The first principles shows that the contribution of Gd near the band gap is small,but increases the intensity of Fe at the bottom of the conduction band,which promotes the transfer of electrons to the Fe-O polyhedra,turning the original indirect band gap into a direct band gap,promoting the electron leap and reducing the energy loss caused by electroacoustic coupling effects.Among different doping contents,10BGFO photocatalyst has the fastest degradation rate,which is significantly higher compared with undoped BFO fibers,and 10BGFO fibers have the fastest charge transfer rate and the highest photogenerated carrier separation efficiency,which can effectively suppress the complexation of photogenerated electrons and holes.(3)BiOI/BFO heterojunction fibers with different BiOI coating amounts were prepared based on the electrostatic spinning process combined with the coating technology.The SPH-BFO fibers were coated with a layer of BiOI nanosheets,and the BiOI nanosheets were uniformly attached to the SPH-BFO fibers.The composite BiOI/BFO fibers have better photocatalytic performance than single BiOI and SPH-BFO fibers.The experiments showed that the 16%BiOI/BFO heterojunction fibers had the highest photodegradation efficiency,and the degradation rate of 10 mg/L rhodamine B reached 98.8%in 30 min.