The Study On The Preparation Of Zinc Stannate And Its Inactivation Performance Against Marine Microorganisms

Ballast water is an essential guarantee for the safe navigation of ocean-going vessels,but its discharge may lead to the invasion of marine organisms in foreign places and pose a great threat to the marine ecological environment.How to treat ballast water effectively,safely,environmentally friendly and economically is a key issue to be solved in this field.Photocatalytic technology provides an effective strategy to solve this challenge.In this thesis,we focus on the performance of zinc stannate photocatalysts to inactivate marine microorganisms.To address the problems of its high photogenerated carrier complexation rate and low light energy utilization efficiency,firstly,Zn₂Sn O₄ is annealed to reduce its surface defects and lower the photogenerated carrier complexation rate;secondly,Zn₂Sn O₄ is doped with metal cations(Ba²⁺)to regulate its energy band position and reduce the forbidden band width;further,Zn₂Sn O₄/Bi₂WO₆ heterojunction is constructed to further,the Zn₂Sn O₄/Bi₂WO₆heterojunction was constructed to enhance the charge separation efficiency.Finally,the performance of Zn₂Sn O₄ inactivation of marine microorganisms was significantly improved,and the main results achieved are as follows:（1）Annealing treatment of Zn₂Sn O₄ can effectively enhance the performance of inactivating its live marine microorganisms.The Zn₂Sn O₄ powder was prepared by hydrothermal method,and the p H value of the hydrothermal reaction was adjusted using Na OH,followed by annealing treatment at different temperatures to improve its photocatalytic performance.The experimental results showed that the prepared Zn₂Sn O₄,which was hydrothermally synthesized,had the optimal photocatalytic performance after annealing treatment at 500°C under the reaction condition of p H 10,with a sterilization rate of 86.46%,which was about four times higher than that of the unmodified Zn₂Sn O₄.This is attributed to the calcination to reduce its surface defects,which leads to an increase in photocatalytic performance and thus carrier separation efficiency.（2）Cation(Ba²⁺)doping of Zn₂Sn O₄ modulates its energy band position to further enhance its photocatalytic performance.the chemical valence of Ba²⁺is the same as that of Zn²⁺and the radius of Ba²⁺is larger than that of Zn²⁺.When Ba²⁺is doped with Zn₂Sn O₄,it leads to lattice distortion.The Ba²⁺-doped Zn₂Sn O₄ nanomaterials with different concentrations were prepared by a common hydrothermal method to study the effect of Ba²⁺doping on the photocatalytic performance of Zn₂Sn O₄ under UV light irradiation.The results illustrate that the photocatalytic activity of Zn₂Sn O₄ is the highest when the doping amount of Ba²⁺is 1 mmol.The sterilization rate could reach 89.2%after 1 h of UV irradiation.The performance enhancement mechanism was attributed to the reduction of the band gap of Zn₂Sn O₄ caused by the doping of Ba²⁺,which in turn enhanced its spectral absorption range and thus improved the photocatalytic performance of Zn₂Sn O₄.（3）Ba²⁺-doped Zn₂Sn O₄/Bi₂WO₆ composites were prepared by constructing heterojunctions,which can significantly enhance the charge separation efficiency of Zn₂Sn O₄and thus improve its photocatalytic performance.The sterilization properties were investigated under UV light irradiation and the effect of Bi₂WO₆ content on the photocatalytic performance of Zn₂Sn O₄ was explored.The experimental results show that the Ba²⁺-Zn₂Sn O₄/Bi₂WO₆composite photocatalytic material has good photocatalytic performance under UV irradiation,and its photocatalytic effect is best when Bi₂WO₆ accounts for 5%of the total mass fraction of the catalyst.The sterilization rate of the composite coating was close to 97%after 1 h of UV light exposure.The improved photocatalytic performance was attributed to the matching energy level structure between Bi₂WO₆ and Zn₂Sn O₄ and the construction of Zn₂Sn O₄/Bi₂WO₆heterojunction,which has a higher valence band potential than Bi₂WO₆,making it easy for holes in the valence band of Zn₂Sn O₄ to jump to the valence band of Bi₂WO₆,while electrons in the conduction band of Bi₂WO₆ to migrate to the conduction band of Zn₂Sn O₄.The electrons in the conduction band of Bi₂WO₆ can easily migrate to the conduction band of Zn₂Sn O₄,thus achieving the efficient separation of electrons and holes in Zn₂Sn O₄.