Modification And Photocatalytic Properties Of Bismuth Iodide-base Photocatalytic Degradation Materials

The problem of water resource pollution is becoming more and more serious.Photocatalysis technology is highly expected in environmental management in recent years.Among all kinds of photocatalytic materials,BiOX（X=Cl,Br,I）semiconductor photocatalyst has narrow band gap width and laminar morphology,which makes it one of the hotspots in photocatalytic materials research.However,BiOX catalyst also has some shortcomings that need to be improved.First,BiOX catalyst has a high electron-hole pair composite rate,and second,it has a poor adsorption performance of pollutants,so it needs to be modified on the basis of BiOX catalyst in order to meet the practical application.Energy gap of BiOI is the narrowest of BiOX,the easier and the narrower the forbidden band width form electronic-hole pair inspired by the light,so this paper mainly study BiOI semiconductor photocatalyst were modified,using solvent hot method（ethanol）was prepared by Br doped in solid solution of BiOI light catalyst,doping on the material of the optical response range and the oxidation reduction potential regulation,make effective light absorption and carrier redox ability to balance,so as to improve the photocatalytic performance of the material.Then,BiOI_0.5Br_0.5,which has the best photocatalytic degradation efficiency,was selected to combine with BiOI to form heterogeneous junction photocatalyst.The formation of heterogeneous junction can reduce the composite efficiency of electron-hole pairs of photocatalytic materials,so as to improve the photocatalytic degradation performance of materials.Firstly,three different solvents（ethanol,water and ethylene glycol）were selected in this paper to successfully prepare BiOI with different morphology at180℃.The composition and morphology of the samples were characterized by X-ray diffraction（XRD）and scanning electron microscopy（SEM）.The optical properties of BiOI were characterized by fluorescence spectroscopy（PL）and u V-visible diffusion spectroscopy（DRS）.The results showed that the BiOI prepared by ethanol had the lowest electron-hole pair compound efficiency and had a better absorption range and response intensity to visible light.The photocatalytic performance of rhodamine B was measured by BiOI degradation rate of 100mg/L.The results showed that the BiOI prepared with ethanol had the highest degradation efficiency,up to 13.9%.Therefore,the BiOI photocatalytic material was prepared by solvent thermal method using ethanol as solvent.Then solid solution photocatalyst BiOI_xBr_1-x（X=0,0.25,0.5,0.75 and 1）with Br doped to BiOI was prepared by solvent thermal method.The composition and morphology of the samples were characterized by XRD,SEM,transmission electron microscopy（TEM）and elemental energy spectrum（EDS）.PL and DRS were used to characterize its optical performance.Bioixbr1-x has a wide visible light absorption range,and the visible light absorption wavelength range is 380nm-600nm.The bioixbr1-x degradation rate of rhodamine B at 100mg/L was investigated to characterize the photocatalytic performance of the material.The results showed that BiOI_0.5Br_0.5 had the best photocatalytic performance,and its degradation rate of Rh B of 100mg/L reached 70.4%.Finally,BiOI_0.5Br_0.5,which has the best performance in the solid solution,was selected for the next heterojunction preparation.Finally BiOI/BiOI_0.5Br_0.5 heterojunction photocatalyst was synthesized.It was found that BiOI/BiOI_0.5Br_0.5 had a lower fluorescence intensity than the solid solution,because the formation of heterojunctions reduced the electron-hole pair recombination rate of the photocatalyst.The positions of the conductive bands for BiOI/BiOI_0.5Br_0.5,BiOI and BiOI_0.5Br_0.5 were calculated by using the electrochemical Motschottky test,and the heterojunction photocatalyst for BiOI/BiOI_0.5Br_0.5 was found to have higher carrier concentration by using the formula.From the dye degradation experiments of BiOI,BiOI_0.5Br_0.5 and BiOI/BiOI_0.5Br_0.5 photocatalysts,it was found that BiOI/BiOI_0.5Br_0.5heterojunction photocatalyst had the best degradation performance.The main reason is that the heterojunction structure increases the carrier concentration and reduces the electron-hole pair recombination efficiency.The trapping experiments of functional groups for BiOI/BiOI_0.5Br_0.5 heterojunction photocatalyst showed that h⁺and·O₂^-were the main photocatalysts.From BiOI/BiOI_0.5Br_0.5 cycle test,it was found that the efficiency of BiOI/BiOI_0.5Br_0.5 was still about 90%after three cycles of use.