Study Of Photocatalytic Disinfection Of M/BiOCl(M=Ag,Ag/AgCl) Nanocomposites

In the thesis BiOCl was modified by a deposition method and light-reduction method to build the photocatalytic materials Ag/BiOCl and Ag/AgCl/BiOCl,which were based on the surface plasmonic resonance of Ag and the surface plasmonic resonance of Ag/AgCl,respectively.The photocatalytic inactivation activity and mechanism of these materials for S.aureus was studied for the first time.The main work can be summarized as follow:1.The Ag/BiOCl binary nanocomposites were synthesized by depositing silver nanoparticles to BiOCl directly.The composition,morphology and optical properties of the obtained sample were characterized by X-ray diffraction?XRD?,scanning electron microscopy?SEM?,energy dispersive spectrometry?EDS?,UV-vis diffuse reflectance spectra?DRS?.It was found that owning to the surface plasmonic resonance of supported Ag,Ag/BiOCl exhibited expandable light absorption,from ultraviolet to visible light area.The photocatalytic disinfection of Ag/BiOCl for S.aureus was studied.The results showed that 1×106 cfu mL-1 of S.aureus was completely inactivated within 6 h under visible light irradiation,exceeding those of pure BiOCl and Ag nanoparticles.The electronic excitation,migration and consumption process of BiOCl and Ag/Bi OCl were analyzed by photocurrent response,photoluminescence spectra?PL?and electrochemical impedance spectroscopy?EIS?experiments.It indicated that Ag/BiOCl binary composites exhibite more effective separation and lower recomnination of electron–hole pair compared to that of pure BiOCl,thus leading to improved photocatalytic performance.The scavengers experiment indicated that the e-,h+ and H₂O₂ were the major reactive species for bacterial inactivation.2.The Ag/AgCl/BiOCl nanosheets were synthesized by a facile situ ion exchange and light-reduction methods.The composition,morphology and optical properties of the obtained sample were characterized by XRD,SEM,transmission electron microscope?TEM?,high-resolution transmission electron microscope?HRTEM?,X-ray photoelectron spectroscopy?XPS?,DRS and nitrogen adsorption-desorption.The photocatalytic inactivation efficiency of Ag/AgCl/BiOCl was evaluated by disinfection of S.aureus under visible light irradiation.For comparison,the disinfection efficiencies over BiOCl,Ag/AgCl,AgCl/BiOCl and Ag/AgCl/TiO₂ were also tested.It was found that when employing Ag/AgCl/BiOCl ternary composites as photocatalyst,1×106 cfu mL-1 of S.aureus was completely inactivated within 3 h under visible light irradiation,which exhibits the best photocatalytic activity.The electronic excitation,migration and consumption process of BiOCl and Ag/AgCl/BiOCl were analyzed by photocurrent response,PL and EIS experiments.It indicated that Ag/AgCl/BiOCl ternary composites exhibited the lower recomnination and more effective separation of electron–hole pair compared to that of pure BiOCl,thus leading to improved photocatalytic performance.Using different scavengers,reactive oxygen species detection and a simple partition system which is able to separate the catalyst and bacteria,the mechanism of photocatalytic bacterial inactivation was further investigated.It was found that the direct contact between Ag/AgCl/BiOCl nanocomposites and bacterial cells was unnecessary for the photocatalytic disinfection,and the H₂O₂ generated from holes reduction via multi-electron pathway on the Ag/AgCl/BiOCl sueface plays an important role in the photocatalytic disinfection.Finally,the structure and morphology of S.aureus at the different stages of photocatalytic inactivation was examined by atomic force microscopy?AFM?.The result illustrates that H₂O₂ produced over Ag/AgCl/BiOCl nanocomposites under visible light irradiation could damage the structure of bacteria cells,and therefore inducing the death of bacterial cells.