Preparation Of TBA/g-C₃N₄-based Photocatalysts And Its Inactivation Of Antibiotic Resistant E.coli

Antibiotic residues in natural water lead to antibiotic resistance of bacteria,and the spread of antibiotic resistant bacteria in the environment causes public health and safety incidents.Photocatalytic technology has the advantages of fast reaction speed,high oxidation efficiency and environmental protection.It is one of the ideal ways to solve the problem of antibiotic resistant bacteria pollution by using solar light as the driving force to inactivate.The key of this method is to select an effective photocatalyst.g-C₃N₄-based materials have a wide prospect in the application of photocatalytic inactivation of antibiotic resistant bacteria due to its advantages of low cost,non-toxic,good stability and suitable band gap.However,g-C₃N₄-based photocatalysts have some disadvantages,such as narrow visible light response range and easy recombination of photogenerated carriers,which limit its practical application.Therefore,it is necessary to improve the photocatalytic inactivation performance by doping and modifying the materials.In this paper,the photocatalyst was modified by thiobarbituric acid,Ag and Ag₃VO₄,aiming at improving the performance of photocatalytic inactivation of antibiotic resistant bacteria by improving the photoresponse ability and the carrier separation effect of the catalyst.On the basis of the above,magnetic recyclable photocatalyst was formed by compounding the material with Fe₃O₄to improve the reusability of the photocatalyst.Therefore,three kinds of g-C₃N₄-based composite catalysts were designed and synthesized in this paper.The tests and analysis were carried out by various characterization methods.In addition,antibiotic resistant E.coli,a common pathogenic microorganism,was used as a model bacterium to study the performance and mechanism of the catalyst inactivation of this bacteria under visible light.The main research contents are as follows:1.In order to improve the visible light absorption capacity of g-C₃N₄,thiobarbituric acid（TBA）as dopant was used to prepare thiobarbituric acid doped g-C₃N₄（TBA/CN）through thermal condensation reaction.A series of Ag/TBA/CN catalysts with different Ag contents were obtained by light reduction method.SEM,TEM,XRD,XPS,UV-vis DRS,PL and EIS were used to characterize the morphology,surface chemical element composition and state,photochemical properties of the catalysts,and the activity of inactivating antibiotic resistance E.coli under visible light was investigated.The results show that Ag/TBA/CN photocatalysts exhibit better inactivation performance than g-C₃N₄ under visible light irradiation.The sterilization efficiency of 6.2 log CFU·m L^-1 E.coli inactivation is achieved within 60 min.Moreover,the photocatalyst has no obvious inactivation in three cycles,the inactivation effect of bacteria is 5.7 log CFU·m L^-1 and has good stability.This is due to the surface plasmon resonance effect of Ag nanoparticles and the role of electron trap,which expand the spectral absorption range and promote the generation of photogenerated charge carriers.2.In order to further improve the inactivation performance of the photocatalyst,Ag₃VO₄/TBA/CN heterojunction photocatalysts with different mass ratios were constructed by in-situ ion exchange method,and characterized to study the composition,structure and photoelectrochemical properties.XRD and XPS results show that Ag₃VO₄ and TBA/CN are effectively combined,and the compound of Ag₃VO₄ does not change the structure of g-C₃N₄ significantly.The results of UV-vis DRS show that the band edge position of the catalyst is red-shifted after Ag₃VO₄ composites and the absorption range of visible light is increased.The experimental results show that Ag₃VO₄/TBA/CN can completely inactivate 7.0 log CFU·m L^-1 of antibiotic resistance E.coli within45 min,and the effect of inactivating 6.1 log CFU·m L^-1 of antibiotic resistance E.coli could still be achieved after three cycles.Since Ag₃VO₄ and TCN compound into the Z-scheme heterojunction,electrons in the conduction band of Ag₃VO₄ directly combine with holes in the valence band of TCN to retain those holes and electrons with strong redox ability,reduce the carrier recombination rate,and thus the photocatalytic activity of Ag₃VO₄/TBA/CN is significantly improved.3.In order to improve the recyclability and reusability of photocatalyst,Ag₃VO₄/TBA/CN/Fe₃O₄ magnetic nanomaterials were prepared by co-precipitation method.The results show that the photocatalyst exhibits excellent photocatalytic activity:the bactericidal effect reached 3.0 log CFU·m L^-1 in 5 min,and 7.0 log CFU·m L^-1 of antibiotic resistant E.coli is completely inactivated in45 min.In the third recycling,all antibiotic resistant E.coli can be inactivated within 45 minutes.Free radical scavenging experiments and ESR results show that·O₂^-and·OH are the main reactive oxygen species in the reaction system.XPS characterization results show that Fe²⁺and Fe³⁺exist in the catalyst.The cycle of Fe²⁺/Fe³⁺driven by visible light can promote the system to produce more reactive oxygen species,which can play an important role in efficient recovery and photocatalytic inactivation.