Synthesis Of Ag/TiO₂ Composite And Its Antibacterial Activity

Human health have been threatened by various bacteria from thousand years ago. People now pay more and more attention to the healthy lifestyle because of the social development, so the research work about antibacterial materials is significant nowadays. Silver-based antibacterial materials have been developed due to its broad antibacterial efficient. However, the antimicrobial activity of Ag NPs was often impeded by the existence of oxidation and aggregation. It is still an attractive challenge to develop new composites which not only can disperse the Ag NPs well but also has an excellent biocidal activity.In this dissertation, a range of spherical and hierarchical Ag/TiO2 composites were produced with the method of morphology-controlled assembly. Based on the results, we proposed the antibacterial mechanism to explain the antibacterial efficacy of the Ag/TiO2 composites. The main results can be briefly described as follows:1. Synthesis of hierarchical flower-like Ag/TiO2 composites and its antibacterial activity. The prepared composites possess hierarchical flower-like structure and high Brunauer-Emmett-Teller (BET) surface area of 131.9 m2?g-1. The amount of silver nanoparticles (Ag NPs) with diameter of 20-40 nm in the composite can be adjusted by the concentration of AgNO3 solution. The antibacterial potency of Ag/TiO2 composites was investigated against Gram-negative bacteria, Escherichia coli (E. coli) and Gram-positive bacteria, Staphylococcus aureus (S. aureus) by determining the minimal inhibitory concentration (MIC), the growth curve of bacteria and zone of inhibition technique. The synergistic effect of Ag NPs and TiO2 lead to superior and long-term antimicrobial activities of the composites with a bacteriostatic rate as high as 99.99%. The mechanism of antibacterial activity of composites was also taken into account by TEM, inductively coupled plasma atomic emission spectrometer (ICP-AES), ultraviolet visible diffuse reflectance spectroscope and fluorescent microscopy.2. Synthesis of spherical and hierarchical Ag/TiO2 composites and their antibacterial properties. The spherical and hierarchical flower-like Ag/TiO2 composites were successfuLly synthesized via the template-induced and solvothermal method based on the Ag/carbon spheres as precursor, respectively. The synergistic effects of release of silver ions and generation of reactive oxygen species (ROS) lead to superior antibacterial efficacy of the composites with a bacteriostatic rate as high as 99% under the xenon lamp. The scanning electron microscopy (SEM) and the fluorescence microscopy showed the integrity of membrane of bacteria was destroyed by adding a given amount of composites in the dark as well. The mechanism of antibacterial activity of composites was also taken into account by carrying out the TEM images of bacteria treated with spherical and hierarchical composites. Based on the results, antibacterial mechanism has been proposed to evaluate the antibacterial efficacy of Ag/TiO2 composite comprehensively.