| Dye wastewater has the characteristics of high chroma and high COD,and contains heavy metals and other substances,which are extremely harmful to humans,other organisms and the natural environment.Common processes for treating dye wastewater have the disadvantages such as high energy consumption and serious secondary pollution.Photocatalytic wastewater treatment technology has the advantages of no secondary pollution,simple installation operation,etc.,but at the same time,there are disadvantages such as low utilization efficiency of light by traditional photocatalysts and difficulty in recycling powdery photocatalysts.Therefore,the preparation of the photocatalyst which is efficient and easy to recycle has become a focus in the field of photocatalytic wastewater treatment.In this study,BiOI was prepared by chemical precipitation method with Bi(NO3)3·5H2O and KI as raw materials,and GO was prepared by modified HUMMERS method with flake graphite,potassium permanganate and NaNO3 as raw materials,Fe3O4 was prepared by coprecipitation method with FeCl3·6H2O and FeSO4·7H2O as raw materials.BiOI/rGO and BiOI/rGO/Fe3O4 composite photocatalysts were prepared by using GO and Fe3O4 as precursors,and the optimum preparation conditions were explored.They were characterized by XRD,FESEM,UV-VIS.Using RhB as the target degradant,the photocatalytic properties of these photocatalysts were investigated by the conditions of illumination time,light intensity,RhB simulated wastewater initial concentration and RhB simulated wastewater initial pH,etc.The main results are as follows:(1)A uniform size,sheet-like flower-like BiOI photocatalyst was prepared by chemical precipitation method,the particle size is between 8.9 and 10.4 μm,the photocatalyst absorption wavelength threshold is 660 nm,and the band gap is 1.73 eV.50 mL,10 mg/L,pH=3 RhB simulated wastewater was treated with 50mg BiOI photocatalyst,and the degradation rate of RhB simulated wastewater could reach 95%after 5h treatment with xenon lamp.(2)GO was successfully prepared by modified HUMMERS,and BiOI/rGO composite photocatalyst was prepared by hydrothermal method with GO,Bi(NO3)3·5H2O and KI as raw materials.When the hydrothermal temperature is 120℃,hydrothermal time is 6 h and the wt of GO is 5%,BiOI/rGO composite photocatalyst has the best degradation effect on RhB simulated wastewater.BiOI sheets and rGO sheets are stacked layer by layer,rGO layer thickness is 12.4 nm-16.1 nm,BiOI sheet thickness is 24.9 nm-29.7 nm,BiOI/rGO composite photocatalyst absorption wavelength threshold is 725 nm,and the band gap is 1.35 eV.50 mL,10 mg/L,pH=3 RhB simulated wastewater was treated with 50 mg BiOI/rGO composite photocatalyst,and the degradation rate of RhB simulated wastewater could reach 98%after 2.5 h Xenon lamp treatment.(3)Fe3O4 was successfully prepared by coprecipitation method.The BiOI/rGO/Fe3O4 composite photocatalyst was prepared by hydrothermal method with GO,Fe3O4,Bi(NO3)3·5H2O and KI as raw materials.When the hydrothermal temperature is 120℃,the hydrothermal time is 6 h,the wt of GO is 5%,and n(Bi):n(Fe)=2,BiOI/rGO/Fe3O4 composite photocatalyst has the best degradation effect on RhB simulated wastewater.BiOI sheet and rGO sheet are stacked layer by layer,Fe3O4 covers both surfaces,rGO layer thickness is 14.4 nm-19.0 nm,average thickness is 15.7 nm,BiOI layer thickness is 25.1 nm-32.0 nm,average thickness is 26.3 nm,the particle size of Fe3O4 is between 27.8 nm and 35.7 nm,and the average particle size is 29.2 nm.BiOI/rGO/Fe3O4 composite photocatalyst absorption wavelength threshold is 710 nm,and the band gap is 1.40 eV.50 mL,10 mg/L,pH=3 RhB simulated wastewater was treated with 50mg BiOI/rGO/Fe3O4 composite photocatalyst,after 7.5 h iodine tungsten lamp treatment,the degradation rate can reach 96%.BiOI/rGO/Fe3O4 composite photocatalyst can be effectively recovered under magnetic field conditions.After five cycles of use,the degradation rate of RhB simulated wastewater can still reach 80%or more. |
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