Synthesis And Photoelectrochemistry Properties Of Visible Light Photocatalyst Of Bismuth Ferrite Compound

Compared with convetional TiO2 based photocatalyst,bismuth ferrite has the smaller band gap(about 2.0 eV),which is conducive to the bismuth ferrite in the visible range with good photocatalytic properties.But low quantum efficiency hindered the bismuth ferrite based catalyst in the visible light photocatalytic and application in the field of organic pollutants.Therefore,many efforts have been devoted to enhancing the photocatalytic efficiency and visible light utilization of bismuth ferrite by controlling its size and shape,doping it with metal ions,and designing relevant nanocomposites.The prepared composite structure,morphology,composition,energy band structure and optical performance were characterized by means of X-ray diffraction(XRD),Raman spectroscopy(Raman),scanning electron microscopy(SEM),X-ray energy spectrum(EDS),X-ray photoelectron energy spectrum(XPS),photoinduced photoluminescence(PL)and ultraviolet visible spectroscopy(UV-VIS).Congo red was used as simulated pollutant of bismuth ferrite composites were study on photocatalytic performance.In this study,bismuth ferrite/graphene doped graphene photocatalysts are successfully prepared by a facile and effective two-step hydrothermal method.Using urea as a nitrogen doped graphene was prepared BiFeO3/N-doped graphene composite materials;at the same time,with sodium sulfide(Na2S)as a sulfur source and reducing agent doped graphene is prepared BiFeO3/S-doped graphene composite materials.XRD,Raman,SEM and EDS indicate that Bi25FeO40 crystalline phase is obtained with the addition of graphene,while BiFeO3 is formed under the same hydrothermal conditions in the presence of N-doped graphene.After the compound sulfur doped graphene,the mixed phase iron oxide(Fe2O3)was introduced into the perovskite phase bismuth ferrite BiFeO3.Core-level and valence-band X-ray photoelectron spectroscopy analyses reveal a downward band bending of bismuth ferrite at the interface of the bismuth ferrite/(N/S-doped)graphene composites,which facilitates the electron transfer from bismuth ferrite to(N/S-doped)graphene and suppresses the recombination of photo-generated electron-hole pairs.This downward bending band alignment at the interface supposes to be the main mechanism underlying the enhanced photocatalytic activity of the bismuth ferrite/graphene composites.PL and UV tests showed that the addition of(nitrogen/sulfur doped)graphene and graphene was beneficial to the absorption of visible light for bismuth ferrite composites.In addition,the effect of the doping amount of nitrogen and sulfur on the photocatalytic energy absorption of bismuth ferrite composite was studied.The photocatalytic activity of graphene composites increased with the increase of nitrogen doping concentration,when the nitrogen doping amount is too high,the photocatalytic activity of BiFeO3/N-doped graphene composites declined.A certain range,doped nitrogen was conducive to reducing the defects on the surface of graphene;when the nitrogen doped amount exceeds a certain amount,nitrogen doped membership increased the defects on the surface of graphene that could influence the electron transfer,which was not conducive to the photogenerated electron hole migration,thereby weakening the bismuth ferrite/nitrogen doped graphene composite photocatalytic activity.And the photocatalytic activity of BiFeO3/S-doped graphene composites were increased with the increase of sulfur doped amount,when the dosage of sulfur content is too low,the photocatalytic activity of BiFeO3/S-doped graphene composites decreased slightly.When the sulfur doped amount was too low and graphene defects could not be reduced,so it failed to improve photoinduced electron transfer.Then increased the amount of doped sulfur could modify graphene surface defects.Compared to the photocatalytic performance reported single-phase bismuth ferrite materials,graphene and nitrogen(sulfur)doped graphene could introduce in a large extent improve the photocatalytic properties of bismuth ferrite composite.In a word,the superior visible light response of bismuth ferrite/graphene microcrystallites make them promising candidates as advanced photocatalysts for water splitting and degradation of organic pollutants.