Study On Preparation And Photocatalytic Properties Of Bismuth Photocatalyst Heterojunction

This paper introduces several kinds of bismuth based photocatalyst and adopts one of the most effective means of modification of photocatalyst-build heterojunction,effectively improve the bismuth based photocatalyst photocatalytic performance.In this paper,we construct three kinds of bismuth based photocatalytic heterojunction respectively:alpha Bi₂O₃/BiOBr,BiVO₄/BiOI and BiOI?010?/BiOCl?001?.1.Prepare different ratio of alpha Bi₂O₃/BiOBr?3.5:1 and 2:1?through the chemical transformation;determine the photocatalytic performance compared to the pure phase structure is effectively improved.The best component proportion of heterojunction is 3.5:1.Photocatalytic degradation of rhodamine efficiency reached90%after 210 min.The morphology was characterized by TEM.The heterojunction is core-shell structure which has ultra-thin BiOBr?about 3 layers?as shell and alpha Bi₂O₃ as core.This makes the alpha Bi₂O₃/BiOBr specific surface area of 38.70 m²/g which is far greater than pure phase component,effectively increasing the photocatalytic reactivity sites.PL analysis on the chromaticity diagram of CM1 has slight blue shift than BiOBr,which proves its forbidden band width decreased and the larger light absorbtion,which is same as ultraviolet diffuse result.Using valence band compensation method to calculate the band structure arrangement,the top of valence band electric potential difference??E_V?is 0.88 eV and the bottom of the conduction band difference value is 0.92 eV,which determine direction of electron transfer of the alpha Bi₂O₃/BiOBr heterojunction is from the conduction band of BiOBr to alpha Bi₂O₃ conduction band,hole is from valence band of alpha Bi₂O₃ to BiOBr valence band.2.The sample of BiVO₄ is successful prepared by the hydrothermal method;further transform to different ratios of?1:0.25,1:0.25,1:0.75,1:1?BiVO₄/BiOI heterojunction through the chemical transformation method.To determine the grain size and morphology by half high width of XRD peaks,SEM and TEM,combined with the preparation process,to explore the formation mechanism of BiVO₄/BiOI.By analyzing the UV-DRS,BiVO4/BiOI?001?,ultraviolet-visible absorption range increases.The best ratio of heterojunction is 1:0.5 which determind by photocatalytic degradation of rhodamine B.The photocatalytic efficiency reached 95%at 100 min.Under the same conditions,a single set of spectral catalyst BiVO₄ and BiOI photodegradation efficiency is less than 50%.At the same time,CM2 photodegradation rate was 0.0317 min^-1,far higher than the pure BiVO₄(0.0032 min^-1)and BiOI(0.0047 min^-1).Photocatalytic performance of the two group was obviously higher than that of pure phase material.The heterojunction band alignment was explored by the valence band compensation method,the VBM of BiVO₄ and VBM of Bi OI energy difference??E_V?is 2.22 eV,the bottom of the conduction band?CBM?difference of them is 1.67 eV.Photoproduction electron transfer to conduction band of BiVO₄ and holes to valence band of BiOI.3.The sample of pure BiOI is successful prepared by the hydrothermal method,further transform to different ratios of BiOI/BiOCl?1:1,2:1 and 4:1,10:1?heterojunction through the chemical transformation method.Photocatalytic degradation of methyl orange?MO?under simulated sunlight,ultraviolet and visible light is used to explore the performance of the photocatalysis.It is found that when I^-:Cl^-=4:1 is the best ratio.Under the simulated sunlight irradiation after 5 h,the degradation efficiency of pure BiOI,BiOCl and ICl41 reached 10.0%,19.8%and72.2%,respectively.Under visible light?>420 nm?,ICl41 samples also showed the highest rate of methyl orange degradation?5 h,38.9%?.ICl41 specific surface area is 33.0749 m²/g,which is far higher than other samples.The photocatalytic performance of heterojunction is significantly higher than the pure material under all kinds of lights.The top of valence band of samples was determined by the means of XPS.The result is that BiOI is 0.30 eV,BiOCl is 1.09 eV and ICl41 is 0.3 eV.Under simulated sunlight,electrons transfer from CB of BiOI?010?to CB of BiOCl?001?.Effective separation photoproducted electrons and holes in heterojunction,which is found by analyzing the band alignment and the larger specific surface area,are favorable to photocatalysis.