Study On Preparation Of Novel Bismuth-based Heterojunction Photocatalyst And Degradation Of Organic Pollutants In Water By One-step Hydrothermal Method

The rapid development of industry not only brings abundant materials to human life,but also brings the problems of environmental pollution,ecological destruction and energy shortage,so people were urgently looking for an efficient and energy-saving way to solve the problem of environmental pollution.Compared with the traditional pollution purification technology,photocatalytic oxidation a green technology which can make use of abundant solar energy to realize the degradation of organic matter.As the core content of photocatalytic oxidation technology,the search for green and efficient visible light catalyst has become the focus of the current research.In recent years,bismuth photocatalysis has gradually attracted the attention of researchers because of its high efficiency,good stability and non-toxicity.In this study,based on bismuth photocatalyst,a new type of bismuth-based heterojunction composite photocatalyst was prepared by one-step method.On the basis of material characterization and analysis,the degradation performance of organic compounds under different conditions was investigated.The photocatalytic mechanism of composite photocatalysts for the degradation of organic compounds was discussed.The specific research contents and results were as follows:（1）A novel heterojunction photocatalyst Bi₂WO₆/Sb₂WO₆was prepared by a one-step hydrothermal method.The morphology,crystal structure,and chemistry of the prepared photocatalyst were analyzed by SEM,TEM,HRTEM,XRD,XPS,UV-Vis DRS,and PL techniques.The state and optical performance were analyzed.Compared with the single Bi₂WO₆ and Sb₂WO₆,the specific surface area of the marigold-like Bi₂WO₆/Sb₂WO₆ were significantly increased,and the adsorption capacity of organic pollutants was significantly improved,and it could provide more photocatalytic active sites;In addition,Bi₂WO₆/Sb₂WO₆ was more effective for visible light.The absorption capacity has been significantly improved,and the photocatalytic degradation ability of organic matter was significantly stronger than that of a single catalyst.The photocurrent and fluorescence experiment results showed that under light conditions,the heterojunction photocatalyst Bi₂WO₆/Sb₂WO₆ presented higher photogenerated carrier current and lower electron-hole recombination rate than a single catalyst.（2）Among the prepared Bi₂WO₆/Sb₂WO₆ photocatalysts,6%Bi₂WO₆/Sb₂WO₆showed the best photocatalytic performance,and the photocatalyst showed high photocatalytic activity for RhB and MO:the photocatalytic degradation rates for RhB（catalyst dosage 0.5 g/L）and MO（catalyst dosage 1.5 g/L）were 100%and 70%,respectively by the treatment of 90 min,and the optimum p H values for the degradation of RhB and MO solution were 7.0 and 3.0,respectively.Under the optimized conditions,the TOC removal rates of RhB and MO by the photocatalyst were 55.3%and 31.5%,respectively by the treatment of 240 min.The results of RhB degradation conducted for five cycles and the XRD patterns of reused photocatalyst,it can be seen that the catalyst has good catalytic and structural stability.（3）On the basis of Bi₂WO₆/BiOI,Bi₂WO₆/BiOI@Ag₃PO₄ heterojunction photocatalyst was prepared by one-step hydrothermal deposition of Ag₃PO₄.Through the analysis of SEM,TEM,HRTEM,XRD,XPS,UV-Vis DRS and PL,it was found that the introduction of Ag₃PO₄ significantly improved the visible light absorption performance of the photocatalyst.The catalyst has flower-like morphology and symmetrical double heterojunction structure.The separation efficiency of e^-/h⁺pairs and the carrier transfer ability were obviously improved.（4）Among the prepared Bi₂WO₆/BiOI@Ag₃PO₄ photocatalysts,Bi₂WO₆/BiOI@Ag₃PO₄-5 showed the best photocatalytic properties for the degradation of organic compounds.The degradations of 20 mg/L BPA（p H=9）,MO（p H=5）,cefepime（p H=6）and TC（p H=9）solutions with 1 g/L photocatalyst presented the degradation rates of 98.1%,98.8%and 96.8%,respectively.The XRD,SEM and FTIR spectra of the reused catalyst showed that Bi₂WO₆/BiOI@Ag₃PO₄ had good photocatalytic stability and photocorrosion resistance.In addition,the biodegradability experiment showed that the biodegradability of cefepime solution was obviously enhanced after photocatalytic degradation.（5）6%Bi₂WO₆/Sb₂WO₆ and Bi₂WO₆/BiOI@Ag₃PO₄-5 heterojunction photocatalysts could degrade organic pollutants under real sunlight,and the organic degradation rate at noon was slightly higher than that under simulated sunlight（300 W）.The results of cyclic degradation experiments and catalyst characterization showed that6%Bi₂WO₆/Sb₂WO₆ and Bi₂WO₆/BiOI@Ag₃PO₄-5 heterojunction photocatalysts have strong photocatalytic stability.The results of free radical capture experiments showed that the active substances h⁺,·O₂^-and·OH were responsible for the degradation of organic compounds in the developed photocatalytic system,and the photocatalytic degradation intermediates of RhB,BPA and Cefepime were analyzed by HPLC,GC-MS and LC-MS,by which the related degradation pathways were proposed.