Study On Photocatalytic Degradation Of 17β-estradiol(E2) By Titanium Dioxide/phosphorene Composites And The Evaluation Of Bioactivity Of E2 After Degradation

Environmental estrogens can enter organisms through air,food,water,and other means,which adversely affect their growth,development,reproduction,and behavior.In order to treat estrogen in sewage,many advanced oxidation methods have been developed,such as composite photocatalysts that support other substances as modifiers on TiO2.However,mostly heavy metals,such as gold and silver,were adopted as modifiers,it not only causes new pollution but also increase operation costs.In this study,selecting 17β-estrogen as target pollutant because of its representativeness and high estrogen activity.Phosphorene(PN),a new twodimensional material with good biocompatibility,was used as modifier to load on TiO2,and PN-TiO2 composites were prepared and used as photocatalysts for E2 degradation.Atomic force microscope(AFM),transmission electron microscope(TEM),field emission scanning electron microscope(FE-SEM),X-ray diffraction(XRD),Raman spectrometer(Raman spectra)and X-ray energy spectrometer(EDS)were used to characterize the morphology and properties of photocatalytic composites.The effects of different PN content in the composite material,the dosage of material in the reaction solution,the pH and temperature of the reaction solution on the performance of the composites were explored,and the kinetic mechanism of the photocatalytic reaction process was developed.To investigate the role of every free radical during E2 degradation,four scavengers were added into reaction solution,and the mechanism and pathway of E2 degradation were inferred according to the result of literatures.Moreover,the development of zebrafish embryos was observed and the gene expression of vitellogenin(VTG)of Bostrychus sinensis was detected,to evaluate the biotoxicity and estrogen activity of E2 after degradation.The main conclusions are listed as follows:(1)PN was prepared by exfoliating the bulk black phosphorous in liquid,and then was loaded onto TiO2 to prepare PN-TiO2 composites.(2)The sharpened edges were observed according to the results of AFM,which implied the low oxidation of PN,and the profile image of PN showed that its thickness was about 3-5 nm.In addition,the lamellar structure was observed through the result of TEM.The result of FE-SEM displayed that TiO2 powders were dispersed well with no agglomeration,and the skeleton structure were intact.The result of XRD showed that the phase structure of the prepared PN and composites was not changed,and no impurities existed.Three characteristic peaks were observed in the Raman spectra of prepared PN,which was similar to that of black phosphorous.Besides,the distance between A1g and A2g of PN was longer,which suggested that the prepared PN was thinner than black phosphorous.However,both characteristic peaks of TiO2 and PN in the Raman spectra of the composites implied that the PN successfully was loaded onto TiO2.The result of EDS also showed that the Ti,O and P elements in the composites existed and mixed well.(3)According to the results of the single factor photocatalytic experiment,it can be known that PN,as modifier,can significantly improve the photocatalysis of TiO2,and PN has greater potential in photocatalysis area.In addition,the composite material had better catalytic performance and economic cost savings when the PN content in the composite was 1.0%.Optimal conditions for the best degradation efficiency of E2 under the irradiation of an 8W ultraviolet lamp were as follows:the solution pH of 5,the temperature of 20℃ and the material dosage of 0.1 g/L.The first 40 minutes of this reaction process accorded with the first-order reaction kinetics and Langmuir-Hinshelwood model,and the fitting correlation coefficients R2 were all above 0.95.(4)According to the results of scavenger experiments,the contribution ration of h+,O2-,1O2 and·OH was 28.50,31.81,11.85 and 27.84%,respectively.According to the result of literatures,the main intermediates of E2 degradation were estrone and 2-hydroxyestradiol.(5)E2 in water environment was able to inhibit the metabolism of water organisms,delay the incubation,and lead to the embryos malformation and even mortality.In addition,E2 could induce the higher expression of VTG gene of water organisms.However,the results of E2 solution after degradation were similar between the aquatic organisms that fed in normal water,which suggested that the degradation of E2 solution had low biotoxicity and estrogen activity.