Preparation And Property Research Of Bismuth Ferrite Micro-nanofibers Fabricated By Electrospinning

In recent years,multiferroic materials have been widely applied in information storage devices,sensors and optics due to their multiferroic properties?such as ferroelectrics and ferromagnetics?and magnetoelectric coupling effects.Bismuth ferrate?BiFeO₃,BFO?with a rhombohedrally perovskite structure exhibits the characteristic of ferroelectric order?ferroelectric Curie temperature T_C¹100 K?and anti-ferromagnetic order?antiferromagnetism Neel temperature T_N⁶40K?at room temperature.Meanwhile,it shows a strong visible light response due to the narrow band gap?E_g=2.0².7 eV?,thus can be used as an excellent photocatalyst.However,some issues including the slower mobility of photogenerated charge carriers,the easy combination of photogenerated electron-hole pairs and lower quantum efficiency of the bulk BFO materials restrict their applications.Several approaches including the construction of one-dimension nanostructure,noble metal loading and semiconductor coupling are proposed to resolve the above issues.In this study,we firstly synthesized BFO nanofibers?BFO NFs?,and then fabricated Au loaded BFO NFs and BiOBr/BiFeO₃ heterojunction.Finally,the ferroelectricity,ferromagnetism and photocatalysis properties as well as the mechanisms were studied.The main research content is as follows.?1?BFO NFs were synthesized by a sol-gel electrospinning method,and the influence of calcining temperature on the morphology,structure,photoabsorbing,multiferroic and photocatalytic properties were investigated.The results show that continuous perovskite BFO nanofibers with smooth surfaces can be obtained at the calcination temperature of 550°C.The average diameter is about 220 nm,but there are some undesirable Bi₂₅FeO₄₀0 impurities.At higher calcination temperature?600°C?,no impurity phase is detected,and the fibers show a more continuous structure with bead string morphologies and smaller diameters.However,the further increasing calcination temperature?approaching 700°C?lead to an irregularly short sticks morphology,caused by the breakup and collapse of BFO NFs.The sample calcined at600°C shows outstanding ferroelectricity,high photocatalytic activity and stability,which can be attributed to better crystallinity,narrower band gap and unique one-dimensional morphology.?2?Novel Au-loaded BFO NFs?Au_x-BFO NFs,x=0,0.6,1.2,1.8,2.4 wt%?were synthesized via a simple reduction method with assist of sodium citrate,and the effect of Au loading amount on the physicochemical properties and photocatalytic activity was investigated in detail.The results show that the reducing condition during Au loading process may promote the formation of BFO nanosheets?BFO NSs?on the surface of BFO NFs,thus obtaining BFO NFs/NSs homojunctions.The number of BFO NSs increases with the increase of the Au loading amount.The Au_1.2-BFO NFs show the best ferromagnetic property and photocatalytic activity.Their catalytic efficiency of methylene blue?MB,15 mg/L?under simulated solar illumination reaches up to 85.76%,much higher than that for pure BFO NFs samples?49.49%,MB,15 mg/L?.The enhanced photocatalytic activity may be mainly attributed to the surface plasmon resonance effect?SPR?of Au nanoparticles,nanofibers/nanoflakes structured homojunction,as well as the generated defects(Fe²⁺/Fe³⁺pairs and oxygen vacancy).Meanwhile,it is proven that holes?h⁺?play the decisive role in the photocatalytic process.?3?BiOBr/BiFeO₃ heterojunction?x%BiOBr-BiFeO₃ NFs,x=5.0,7.5,10.0,molar values?photocatalysts were synthesized by the coating method,and the physicochemical,ferroelectric and photocatalytic properties were discussed.All the BiOBr-BiFeO₃ NFs show excellent ferroelectric and ferromagnetic performance.With the increase of the coating amount of BiOBr,the band gap energies of BiOBr-BiFeO₃NFs increase slightly.7.5%BiOBr-BiFeO₃ NFs show the lowest photoluminescence?PL?intensity,which is beneficial to lower the compound probability of photogenic cavitation-electron pair.This sample shows excellent stability and the best photocatalytic performance.Its catalytic efficiency of MB?20 mg/L?under simulated solar illumination reaches up to 74.84%,much higher than that for pure BFO NFs?30.48%,MB,20 mg/L?,illustrating that the BiOBr/BiFeO₃ heterojunction may dramatically improve the photoactivities.In summary,the issues inhibiting BFO materials including the slower mobility of photogenerated charge carriers,the easy combination of photogenerated electron-hole pairs and lower quantum efficiency can be effectively resolved by construction of one-dimension nanostructure,noble metal loading and semiconductor coupling.This study is of great significance for improving the degradation efficiency of organic dyes such as MB.