Study On Photocatalytic Degradation Of Tetracycline By Ag₂CO₃/Bi₄O₅I₂/g-C₃N₄ Composites

In recent years,various organic pollutants in wastewater have seriously threatened aquatic ecosystems and human health,especially water pollution caused by antibiotics.At the same time,the application of semiconductor photocatalysis technology in water purification has been paid more and more attention.Currently,the construction of step-scheme（S-scheme）heterojunction has proved to be a promising method to improve the degradation performance of photocatalysts.Importantly,S-scheme heterojunction system shows great potential in accelerating the separation and transformation of photogenerated carriers and obtaining strong light oxidation ability.In this paper,g-C₃N₄was modified by constructing a complex.The morphology,structure and composition of photocatalysts were analyzed by a series of characterizations.The reaction mechanism of tetracycline（TC）degradation under visible light was investigated.The main research results are:The selection of suitable cocatalysts is the key to the construction of ternary g-C₃N₄-based photocatalysts.Among various cocatalysts,Bi₄O₅I₂and Ag₂CO₃may be good candidates due to their good physical,chemical and optical properties.Ag₂CO₃and Bi₄O₅I₂photocatalyst materials show high photocatalytic performance due to their suitable band gap positions and strong responses in the visible region.First,Bi₄O₅I₂is listed as a promising photocatalyst due to its special internal layered structure,broad photoresponse range,and excellent chemical stability.Second,Ag₂CO₃is often used as a cocatalyst in photocatalysts because of its excellent optical properties and small bandgap energy.In particular,due to the high VB site of Ag₂CO₃,Ag₂CO₃is always used to construct heterojunctions to maintain its strong oxidation potential and facilitate photoinduced charge transfer.However,the applications of Ag₂CO₃and Bi₄O₅I₂photocatalyst materials are limited due to their narrow visible light response and high photogenerated carrier recombination rate.As a"sustainable"functional material,g-C₃N₄has strong stability and high photocatalytic activity,which greatly promotes the degradation of organic matter.However,the low electrical conductivity and limited specific surface area of?g-C₃N₄limit its application in the field of photocatalytic degradation of antibiotics.To overcome these shortcomings,g-C₃N₄can be combined with other compounds to improve its performance by adjusting the mass fraction ratio.And considering the advantages of Bi₄O₅I₂and Ag₂CO₃and their well-matched band positions with g-C₃N₄,it may be a good strategy to use them together to modify g-C₃N₄.In this paper,Ag₂CO₃/Bi₄O₅I₂/g-C₃N₄dual S-scheme heterojunction material was designed and constructed by heat treatment and subsequent in-situ wet chemistry.Compared with the original Bi₄O₅I₂and g-C₃N₄,Ag₂CO₃/Bi₄O₅I₂/g-C₃N₄hybrid catalyst showed remarkably enhanced photocatalytic performance in tetracycline degradation.The tetracycline degradation rate constant of Ag₂CO₃/Bi₄O₅I₂/g-C₃N₄is 0.03892 min^-1,which is about 2.09,5.80 and 13.33 times higher than that of pure Ag₂CO₃(0.01865 min^-1),Bi₄O₅I₂(0.00671 min^-1)and g-C₃N₄(0.00292 min^-1),respectively.The apparent enhancement of photocatalytic activity is not only due to the formation of ternary complex,which can enlarge the visible light response of g-C₃N₄,but also due to the S-scheme heterojunction.When the interface is illuminated by visible light,the establishment of the built-in electric field and the resulting bending of the band edge promote the recombination of photogenerated carriers with weaker redox ability in the composite while retaining electrons and holes with stronger redox ability.Therefore,the residual electrons and holes with high reducing and oxidizing properties endow the composite with extremely high redox ability.The mechanism of dual S-scheme heterojunction photocatalyst was studied and discussed.This study expands the application range of g-C₃N₄material,and also discusses the reaction mechanism of Ag₂CO₃/Bi₄O₅I₂/g-C₃N₄composite material in dual S-scheme reaction system in detail.In conclusion,Ag₂CO₃/Bi₄O₅I₂/g-C₃N₄dual S-scheme heterojunction materials were constructed by heat treatment and co-precipitation.The ESR analysis provides the basis for elucidating the charge transfer of the double S-scheme heterojunction in the Ag₂CO₃/Bi₄O₅I₂/g-C₃N₄composite sample during the photocatalytic process.The TC degradation efficiency of Ag₂CO₃/Bi₄O₅I₂/g-C₃N₄heterojunction material is greatly improved,which is about 13.33 times higher than that of pure g-C₃N₄.The existence of the stepped heterojunction accelerates the recombination of the relatively useless e^-and h⁺,and reduces the recombination of the relatively useful e^-and h⁺,thus providing a strong driving force for the photocatalytic degradation of TC.Importantly,this work demonstrates an efficient synthetic strategy for the construction of dual S-scheme heterojunction materials,providing insight into the optimization of semiconductor photocatalysts.