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Abstract
Silver nanoparticles (AgNPs) are widely used as antibacterial due to enhanced diffusivity, high reactivity against a wide range of microbes and parasites, low dose and low propensity to induce microbial resistance. As a result of the widespread use, AgNPs will inevitably be released into environment which may have an impact on natural ecosystems.
The redox transformations of AgNPs were studied with the thesis divided into 4 parts. The first part focuses on the kinetics and mechanism of AgNPs oxidative dissolution by chlorine, which may be used as disinfectant in wastewater treatment plant. In the second part, we investigate the regeneration of semiconducting AgCl(s) by chlorine mediated oxidation of photo-reduced Ag(0). Oxidation rate of formic acid caused by photocatalytic AgCl(s) was used to quantify the ability of AgCl(s) in degrading organic contaminants and regeneration rate of AgCl(s) by the presence of chlorine. Effect of pH on the regeneration rate of AgCl(s) has been also investigated. The third part focuses on the impact of light and natural organic matters (NOM) on dioxygen and H2O2 mediated oxidation of AgNPs in natural waters with the aim to determine the mechanisms via which NOM affects the oxidative dissolution of AgNPs, the role of photo-generated reactive oxygen species (ROS) in AgNPs oxidation and the mechanism of AgNPs formation in irradiated solution containing NOM and Ag(I). In the fourth part, a commercially available AgNPs dietary supplement, MesosilverTM, was used to investigate Ag(I) release and ROS generation at pH 2.0-7.0 typical of human digestive system. The effect of chloride was also investigated as high concentration of chloride is expected in human gut.