Impact of light and Suwanee River Fulvic Acid on O_2 and H_2O_2 Mediated Oxidation of Silver Nanoparticles in Simulated Natural Waters

摘要

In this work, we investigate the impact of natural organic matter (NOM) and light on silver nano particle (AgNP) dissolution kinetics with particular emphasis on determining the (i) mechanism via which NOM affects the oxidative dissolution of AgNPs, (ii) the role of photo generated organic radicals and reactive oxygen species (ROS) in oxidative dissolution of AgNPs, and (iii) the mechanism of formation of AgNPs in NOM solution under dark and irradiated conditions. We measured the oxidation of citrate stabilized AgNPs by O-2 and hydrogen peroxide (H2O2) in the dark and in irradiated Suwannee River fulvic acid (SRFA) solutions at pH 8.0. Results show that the reactivity of AgNPs toward O-2 and H2O2 in the dark decreased in the presence of SRFA as a result of blocking of AgNP surface sites through either steric or electrostatic effects. Irradiation promoted dissolution of AgNPs by O-2 and H2O2 in the presence of low concentrations (= 20 mg.L-1) of SRFA as a result of contribution from photogenerated H2O2 formed on irradiation of SRFA as well as photofragmentation of AgNPs. Furthermore, our results show that photogenerated superoxide can induce formation of AgNPs by reducing Ag(I) ions. Based on our experimental results, we have developed a kinetic model to explain AgNP transformation by O-2 and H2O2 in the dark and in irradiated SRFA solutions with this model of use in predicting the transformation and fate of AgNPs in natural waters.