Study On Preparation,Characterization And Antibacterial Activity Of Heterogeneous Composite Photocatalyst Based On TiO₂ And WO₃

Food safety tragediescaused by pathogens have recently come into the public focus and thus aroused worldwide attention.To solve the food safety problems of this kind,lots of researchers have tried,experimented and tested in various ways.Semiconductor photocatalysis,a novel method of antibacterium,has attracted much attention of researchers and admittedly regarded as one of the most promising solutions.Beinga “green” antibacterial technology with the characteristicsof high efficiency,broad-spectrum,andlonger durability,it is not easy to cause resistance and not liable to bringing about secondary pollution.However,the pure semiconductor material has limited antibacterial effect.Some of them can be made excitedby ultraviolet or near-ultraviolet radiationonly,limiting its antibacterial properties.Modification to the materials can significantly improve their antibacterial properties.Under such circumstances,this thesis is mainly to discuss the improvement of nano-materials in the visible light absorption which are modified by the method of noble metal deposition and recombination with semiconductor.The composite photocatalysts with different characteristics are synthesized by solvent thermal method and Escherichia coli K12 is chosen for antibacterial capability experiment.First of all,TiO₂ was modified with Au and Ag nanoparticles respectively which was chosen as modifing material.Au and Ag particles on the surface of TiO₂ can effectively enrich electrons and increase the surfaceplasmon resonance effect of TiO₂,which is contributes to the formation of electron-hole pairs and improve the visible light absorption.In this study,Au/TiO₂ composites were synthesized with different contents of Au of 0%,0.5%,1%,3% and5%.The results showed that the Au/TiO₂ composite materials not only had strong optical absorption in the UV region but also had a strong absorption peak at a wavelength of about550 nm of the visible region??> 400nm?.On the other hand,the Au nanoparticles reunited together with the increase of Au content which caused reducing of SPR effect,reduced the absorption of visible light.The survival rate of 0%,0.5%,1%,3%,and 5% Au/TiO₂ composites after 5h visible light irradiation were 85.7%,44.2%,32.4%,52.7% and 54.8%,respectively.Among them,1% Au/TiO₂ had excellent visible light absorption and bactericidal properties on E.coli.This ability with visible light absorption of Au/TiO₂ nanoparticles resulted from SPR effect caused by noble metal doped Au,and AgCl can make TiO₂ sensitive.Then,a series of Ag/AgCl/TiO₂ composite materials owning SPR effect and two dimensional Na₂W₄O₁₃ flake mixed with 0 dimensional WO₃ and PdO were developed by one-step method based on Au/TiO₂ nanoparticles synthesis method,and results showed that the two kinds of materials had highly absorption in the visible region and photocatalyticdisinfection performanceon Escherichia coli.The as-prepared nanocomposites of 10% Ag/AgCl/TiO₂ displayed highly photocatalytic activity,which could disinfect almost all of the Escherichia coli after 40 min treatment.The PdO nanoparticle of 2-D PdO/WO₃/Na₂W₄O₁₃ composites was used as electron-hole pair separation centers to trap the photo-generated electron and reduce the recombination of photo electron-hole pairs to improve the photocatalytic efficiency.The as-prepared nanocomposites of 0.5% 2-D PdO/WO₃/Na₂W₄O₁₃ displayed highly photocatalytic activity,which could disinfect 98.7% of Escherichia coli after 5h treatment.The results above proved that modification to nanocompositescan significantly enhance the photocatalytic properties,and also are capable to kill food pathogenic bacteria?Escherichia coli?.The enhanced photocatalytic activity was due to themodification to nanocomposites which changed its optical characteristic.The mechanism of itsantibacterial activity was attributed to ·OH originated from photocatalysis by the heterostructurecomposites.