The Study Of Preparation Of Bismuth Vanadate-based Composite Photocatalyst And Its Application In Wastewater Treatment

China has a large population and both agriculture and animal husbandry are relatively developed.Therefore,the huge environmental residue caused by the massive use of antibiotics in our country has seriously endangered people’s health.Compared with traditional treatment methods（such as physical and biological treatment technologies）,the photocatalytic oxidation method can degrade antibiotics completely in wastewater by using active substances generated by photocatalytic semiconductors under illumination.At the same time,it has such advantages as simple reaction process,low reaction cost and so on.Bismuth vanadate is a lanthanide photocatalytic semiconductor.It stands out among many photocatalysts with high stability and good visible light response.However,the photo-generated Electron hole pairs generated by pure BiVO₄ under the photocatalytic reaction are easy to combine,thus affecting its photocatalytic effect to a certain extent.In this paper,Fe₃O₄/MoS₂/BiVO₄,Ag₃PO₄/Cu-BiVO₄ and AgI/ZnIn₂S₄/BiVO₄ composite photocatalysts were prepared by composite modification of Bismuth vanadate and photocatalytic semiconductor.The performances of which were studied by analyzing characterizations of XRD,SEM,FT-IR,UV-vis,XPS,photocurrent response and EIS.Photocatalytic experiments were carried out with tetracycline hydrochloride（TC）as the target pollutant under xenon lamp irradiation to study the degradation ability of samples on TC.The stability and reusability of the samples were studied through cyclic experiments.The reasons why the photocatalytic performance of the samples was greatly improved were found and verified through capture experiments.The main contents of this paper are as follows:（1）The composite photocatalyst with Magnetic Fe₃O₄/MoS₂/BiVO₄ was prepared by hydrothermal method.It was found that the degradation rate of TC in photocatalytic reaction was much higher than that of pure BiVO₄.Its degradation rate of TC can reach 85%when the prepared sample was under the condition that the molar ratio of bismuth to molybdenum was30,and the photocatalytic performance was the best.Capture experiments and ESR results showed that OH,h⁺and·O₂^-three free radicals were produced by the sample in photocatalytic reaction,which degraded TC together.The sample with good magnetism can be quickly recovered under the action of an external magnetic field due to the addition of Fe₃O_4.It still had high degradation rate to TC though reused for 5 times.The improvement of photocatalytic performance of the sample was the result of the p-n heterostructure combined by MoS₂ and BiVO₄,which functions as accelerating the separation of photo-generated electron-hole pairs and prolonging the life of photo-generated carriers.（2）The composite photocatalyst Ag₃PO₄/Cu-BiVO₄ was prepared by hydrothermal method and in-situ precipitation method.The photocatalytic performance of the prepared sample was the best when the molar ratio of bismuth to silver was 2.The UV-vis results showed that the absorption sideband of the sample had red shift,which improved the response range and utilization efficiency to visible light.It was consistent with the transient photocurrent response and EIS results.In 120min photocatalytic reaction,the degradation rate of TC can reach 91.6%,and rhodamine B dye wastewater can be completely degraded within 30min.The results of cyclic experiments showed that the sample had good stability and reusability.Finally,the discussion on the mechanism of improving photocatalytic performance of the samples was conducted.The conclusion was that Ag₃PO₄/Cu-BiVO₄ composite photocatalyst doped Cu²⁺and formed a staggered gap type heterostructure,which can accelerate the transfer rate of photo-generated carriers,improve the separation rate of photo-generated electron-hole pairs and inhibit their recombination.（3）The composite photocatalyst AgI/ZnIn₂S₄/BiVO₄ was prepared by hydrothermal method and in-situ precipitation method.Photocatalytic reaction of pure AgI,pure BiVO₄ and samples under visible light showed that the degradation effect and degradation rate of samples on TC were much higher than those of the two pure substances.When the molar ratio of BiVO₄to AgI was 1,the degradation rate of TC can reach 83%.Cyclic experiments on the samples proved that the samples had good stability and can degrade TC wastewater efficiently for many times.Through the capture experiment,it was found that h⁺and·O₂^-radicals were generated in the sample under the photocatalytic reaction,which worked in the degradation of TC involved in wastewater.The reason why the photocatalytic performance of the sample was improved was that the formed ternary Z-scheme heterostructure can enable electrons to be transferred more efficiently within the sample and improve the separation efficiency of photo-generated electron-hole pairs.