The Design Of Three Heterojunction Photocatalysts And Their Performance Evaluation In Treating Normal Pollutant And Fracturing Flowback Fluid

Aming at the serious water pollution problem,photocatalysis is an environmental method with the properties of high efficiency and no secondary pollution.In this paper,based on Ag Br,three visible light responsive photocatalysts was designed by constructing heterojunction.The separation rate of photogenerated carriers was promoted.Ag Br/Ce O₂,Ag Br/Bi₂S₃,Ag₂S/Zn In₂S₄ exhibited an good photocatalytic performances for degrading rhodamine B（Rh B）,methyl orange（MO）,tetracycline（TC）,inhibiting the growth of Escherichia coli（E.coli）,and decomposing water to produce hydrogen.It also played a role in that photocatalysis was involved in the treatment of fracturing flowback fluid.（1）Flower-like CeO₂ was prepared via the ice-bath coprecipitation method,which could provide the big contact interface.Then Z-scheme Ag Br/Ce O₂ heterojunction photocatalysts were synthesized via a facile deposition–precipitation method.The Ag Br mass fraction in the composites were altered,40 wt%-Ag Br/Ce O₂ exhibited optimal photocatalytic activity.Following visible light irradiation for 180 min,the degradation rates of Rh B and MO by 40 wt%-Ag Br/Ce O₂reached 96%and 93.4%,respectively.And99.7%E.coli disinfection was achieved in the presence of this photocatalyst.Under the visible light irradiation for 120 min,the degradation rate of TC was 77.8%.Due to the formation of Z-scheme heterojunction,40 wt%-Ag Br/Ce O₂ possessed abundant Ce³⁺and oxygen vacancies,higher redox capacity and separation efficiency of photogenerated charge carriers..O₂^-,.OH,and h⁺played important roles in the photocatalytic process.（2）Flower-like Bi₂S₃ was prepared by a hydrothermal method,then the Z-scheme AgBr/Bi₂S₃ heterojunction photocatalyst was prepared by a facile deposition-precipitation method,and the Ag Br mass fraction in the composites was altered,90 wt%-Ag Br/Bi₂S₃ presented optimal photocatalytic property.Under the visible light illumination for 80 min,the removal rate of Rh B by 90 wt%-Ag Br/Bi₂S₃ was 98.93%;Under the illumination for 120 min,the removal rate of TC was 60.52%;Under the illumination for 180 min,the bacteriostatic rate of E.coli was 99.9%.On account of the formation of Z-scheme heterojunction,90 wt%-Ag Br/Bi₂S₃ performed higher redox capacity and separation efficiency of photogenerated charge carriers,.O₂^-,.OH,and h⁺played major roles in photocatalytic process.（3）Flower-like ZnIn₂S₄ was prepared by a hydrothermal method,type I-scheme Ag₂S/ZnIn₂S₄was prepared by a ultrasonic method with Ag Br and Zn In₂S₄,Ag₂S/Zn In₂S₄-1 was prepared by adding 1 wt%Ag Br,which performed the best photocatalytic property of hydrogen evolution.Under the irradiation of visible light for 4h,the hydrogen production of Ag₂S/Zn In₂S₄-1 was 468.7μmol by loading 1 wt%H₂Pt Cl₆cocatalyst,and the hydrogen evolution rate was 2343.5μmol/h/g.Under the visible light irradiation for 120 min,the degradation rate of TC was 89.8%.After the formation of type I heterojunction,the bigger specific surface area and higher separation rate of photogenerated charge carriers enhanced the photocatalytic performance for Ag₂S/Zn In₂S₄-1.（4）40 wt%-Ag Br/CeO₂,90 wt%-Ag Br/Bi₂S₃,Ag₂S/ZnIn₂S₄-1 were used for the treatment of fracturing flowback fluid.Combining fenton oxidation,catalytic ozonation and photocatalysis to treat the laboratory self-made fracturing fluid,the COD removal rate could reached up to 87.6%.Flocculation-fenton oxidation+adsorption-catalytic ozonation-photocatalysis were used together to treat the fracturing flowback fluid from Qinghai oilfield,The COD removal rate was 94.4%,the TOC was reduced by 87%,respectively.The contents of harmful components decreased obviously.After the treatments,the water quality all reached the standard of reusing,Ag₂S/Zn In₂S₄-1 showed the best photocatalytic activity,.O₂^-、h⁺、e^-played major roles in the photocatalysis treatment of fracturing flowback fluid.