Photocatalytic Degradation Of Pathogenic Bacteria By Highly Efficient Photocatalysts

The objective of this thesis is discussing efficient heterogeneous photocatalysts for removal mechanism of pathogenic bacteria in aqueous environment. The main research contents and results are shown as following.Hydroxyapatite was co-substituted with Ti(IV) and antibacterial ions (Ag⁺, Cu²⁺ ,Zn²⁺) by coprecipitation and ion-exchange methods. Both HAPTiAg and HAPTiCu coated on porous spumous nickel film showed high efficiency for killing Escherichia coli and Staphylococcus aureus in the dark and under weak UVA irradiatiom, respectively. Moreover, their bactericidal activities were much higher than that of TiO₂ fillm. The studies of ESR revealed that not only O₂^·- was formed on HAPTiM, HAPTi, HAP and P25-TiO₂ films under weak UVA irradiation, but also at ambient temperature without light O₂^·- was generated on HAPTiCu, HAPTiAg, and HAPTi. The redox couples of Cu⁰/Cu²⁺ and Ag⁰/Ag⁺ in the structure of HAPTiCu(Ag) caused the transfer of eletron leading to the O₂^·- generation under the above conditions. The higher bactericidal activities of HAPTiM were due to the synergy of the oxidation role of the O₂^·- and the bacteriostatic action of antibacterial ions.The photocatalytic inactivation of pathogenic bacteria in water was investigated systematically with NiO/SrBi₂O₄. 7.5 log E.coli. was almost completely killed within 50min in NiO/SrBi₂O₄ suspension under visible light irradiation. ESR studies confirmed that the photocatalytic oxidation mechanism of materials under visible light irradiation. The decomposition process of the cell wall and the cell membrane was directly observed by TEM and further confirmed by K⁺ leakage from the killed bacteria. The possible cell damage mechanisms by visible-light-driven NiO/SrBi₂O₄ are proposed. In addition, the effects of pH, methanol and inorganic ions on bacterial photocatalytic inactivation were experimented.The photocatalytic disinfection of pathogenic bacteria in water was investigated systematically with AgI/TiO₂ under visible light (λ>420 nm) irradiation. The ^·OH_ad and h_VB⁺ on the surface of the catalyst were possibly main active oxygen species by the studies of electron spin resonance and the effect of radical scavengers. The process of destruction of the cell wall and the cell membrane was verified by TEM, potassium ion leakage, lipid peroxidation and FTIR measurements. Some products from photocatalytic degradation of bacteria such as aldehydes, ketones, and carboxylic acids were identified by FTIR spectroscopy. These results suggested that the photocatalytic degradation of the cell structure caused the cell death. The electrostatic force interaction of the bacteria-catalyst significantly affected the efficiency of disinfection on the basis of the E. coli inactivation under different conditions.