Preparation Of Bi-based Pyrochiorite Z-type Heterojunction Photocatalyst And Its Degradation Performance Of Tetracycline

In recent years,antibiotic pollution has increasingly attracted the attention of researchers.Tetracycline,due to its stable properties,is difficult to be completely degraded in the environment and accumulates continuously,causing serious environmental pollution and adversely affecting human health and ecosystems.As a new technology for degrading pollutants,photocatalysis has the advantages of cheap,high efficiency and cleanliness,so it has been widely favored in the environmental field.In this study,based on the analysis of the photocatalytic performance of the bismuth-based pyrochlore(Bi2Zr2O7),semiconductor materials such as g-C3N4 and Ag3PO4 with suitable conduction band and valence band positions and good visible light response ability were selected to combine with them.The construction of composite Z-type heterogeneous materials was studied and a composite Z-type heterojunction photocatalyst was constructed.Tetracycline was used to remove pollutants,and the photocatalytic performance of the catalyst and its influencing factors were analyzed.First,photoreduction method was used to prepare the all-solid-state Z-type heterojunction g-C3N4/Ag/Bi2Zr2O7(Ag-CN)composite photocatalyst,and the photocatalyst was analyzed and characterized by various characterization methods.SEM and TEM image analysis showed that the composite g-C3N4 had a two-dimensional nanosheet structure,which was caused by the stripping effect of silver nanoparticles(Ag NPs).By reducing Ag+to Ag NPs,Ag NPs were deposited on the surface of g-C3N4 and Bi2Zr2O7,so as to enter between the sheets of g-C3N4 and achieve stripping.The results of BET analysis showed that the specific surface area(SBET)of the composite photocatalyst was significantly increased.Among them,the SBET of Ag-CN-3 was 17.1 m2/g,which increased by 23.9%and 15.6%compared with Bi2Zr2O7 and g-C3N4,respectively.The increased SBET provides more active reaction sites,which was favorable for the redox reaction on the photocatalyst surface.The photocatalytic degradation and cycling test of tetracycline showed that Ag-CN-3 exhibited the best photocatalytic effect and good stability.The removal rate of tetracycline could reach 81.5%after 75 min of light.Through UV-Vis,free radicals masking experiment and ESR analysis.the photocatalytic mechanism of the composite photocatalyst was explored.The results showed that OH and O2-and h+play an important role in the degradation of tetracycline,which were in line with the all-solid-state Z-type heterostructure photocatalytic mechanism.The all-solid-state Z-type heterojunction structure constructed in this study not only reduced the recombination rate of e-and h+,but also improved the redox capabilities of both.In order to further improve the photocatalytic performance,Bi2Zr2O7/g-C3N4/Ag3PO4(BCA)composite photocatalysts were synthesized by in-situ precipitation method.The physical and chemical properties of the prepared photocatalyst were characterized by various characterization methods.The photocatalytic performance of the prepared photocatalysts were evaluated by the photodegradation rate of tetracycline under visible light.In contrast,BCA-10%had the best photocatalytic degradation effect on tetracycline under visible light,and the degradation efficiency could reach 86.2%.The results of the cycle experiment showed that the BCA-10%composite photocatalyst still has high photocatalytic activity after 5 cycles of experiments,so it had good stability,which is of great significance to the application of the photocatalyst.The enery band gap(Eg)as well as the valence band and conduction band positions of g-C3N4,Bi2Zr2O7 and Ag3PO4 were analyzed according to the UV-Vis DRS spectrum.The Eg of g-C3N4,Ag3PO4 and BZO were 2.70,2.41 and 2.82 eV,respectively.The valence band positions were 1.58,2.67 and 2.96 eV,respectively.And the corresponding positions of the conduction bands were-1.12,0.26 and 0.15 eV.Studies had shown that the main active substances in the BCA-10%photocatalytic system were·O2-,h+ and·OH,which conformed to the double Z-type heterojunction photocatalytic mechanism.And according to mass spectrometry,the three possible degradation pathways of tetracycline were deduced.In this study,the double Z-type heterojunction was constructed successfully,which is beneficial to improve the quantum efficiency and e--h+separation efficiency,and effectively improves the photocatalytic performance of the photocatalysts.