Preparation And Photocatalytic Sterilization Of Bi₂O₂CO₃ Composite Coatings

Water is an indispensable part of human life,because it is essential for drinking,food processing and industrial manufacturing.Water is equally important in the course of a ship’s voyage.There are a lot of harmful impurities and different kinds of pathogenic bacteria in ballast water produced during ship sailing.Moreover,the living microorganisms enter the new ecosystem with the ship sailing,which destroys the stability of the environment and even endangers human health.Ship ballast water must therefore be properly treated to kill all pathogenic microorganisms.Semiconductor photocatalytic technology has been proved to be an effective means to inactivate Marine microorganisms.In this thesis,Bi₂O₂CO₃photocatalyst as the main material,using two different noble metals（Ag,Bi）deposition and narrow band gap semiconductor g-C₃N₄coupling method to improve the photocatalytic activity of Bi₂O₂CO₃photocatalyst,so as to achieve efficient inactivation of bacteria in ship ballast water.The research work is summarized as follows:（1）Petal-like microspheres loaded with precious metal Ag were prepared by one-step hydrothermal method combined with optical deposition.Under the irradiation of visible light,0.7%Ag/Bi₂O₂CO₃composite photocatalyst embodies the perfect photocatalytic sterilization efficiency,and 0.7%Ag/Bi₂O₂CO₃composite photocatalyst has the highest photocarrier separation efficiency,and the sterilization rate is twice that of pure Bi₂O₂CO₃.The results showed that the surface plasmon resonance effect of Ag nanoparticles extended the spectral response of the Ag/Bi₂O₂CO₃composite photocatalyst to visible light,enhanced the environmental stability of the photocatalyst,and improved the photocatalytic sterilization rate significantly.（2）Bi/Bi₂O₂CO₃composite photocatalyst was prepared by solvothermal method,and its purification of ship ballast water was investigated.This synthesis method enables Bi nanoparticles to be generated in situ on the surface of petal-like Bi₂O₂CO₃microspheres.The combined characterization shows that the 3BBOC composite sample has the highest photocatalytic sterilization efficiency in seawater samples.The SPR effect of Bi/Bi₂O₂CO₃heteropair enhanced the absorption of Bi/Bi₂O₂CO₃heteropair spectrum,and also improved the adaptability and The SPR effect of Bi/Bi₂O₂CO₃heteropair in situ improves the absorption degree of Bi/Bi₂O₂CO₃heteropair spectrum,and also improves the adaptability and durability of environment.Free radical capture experiment showed that hydroxyl radical（·OH）was the most efficient free radical to kill bacterial pathogens in ship ballast water.（3）The surface modification of Bi₂O₂CO₃by g-C₃N₄was introduced to solve the problem of limited spectrum utilization caused by wide band gap of Bi₂O₂CO₃photocatalyst,so as to improve its photocatalytic activity.The g-C₃N₄/Bi₂O₂CO₃heterojunction was fabricated and investigated by traditional hydrothermal method and simple ultrasonic-assisted method.The photocatalytic bactericidal activity was verified and the photoinduced electron-hole pairs were separated efficiently.The sterilization degree of 10CNB composite photocatalyst to ship ballast water was the highest,reaching 95%.Through the detection of active substances,hydroxyl radical（·OH）plays an important role in photocatalytic sterilization process.