Impact of light and Suwanee River Fulvic Acid on O₂ and H₂O₂ Mediated Oxidation of Silver Nanoparticles in Simulated Natural Waters

Abstract

In this work, we investigate the impact of natural organic matter (NOM) and light on silver nanoparticle (AgNP) dissolution kinetics with particular emphasis on determining the (i) mechanism via which NOM affects the oxidative dissolution of AgNPs, (ii) the role of photogenerated 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 O2 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 O2 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 O2 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 O2 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.

Copper, silver, and titania nanoparticles do not release ions under anoxic conditions and release only minute ion levels under oxic conditions in water: Evidence for the low toxicity of nanoparticles

“…This indicates that dissolved oxygen in solution plays a pivotal role in releasing dissolved metal ions from nanomaterials. Previous investigations in the case of silver nanoparticles also showed similar observations, e.g., Ag 0 + O 2 → Ag + + O 2 − (He et al 2011(He et al , 2012Rong et al 2019). Figure 2 shows the generation of reactive oxygen species from the surfaces of each nanomaterial used in the study after 15 min irradiation with ultraviolet light.…”

“…The literature has shown that silver nanoparticles have the ability to generate reactive oxygen species with and without ultraviolet irradiation. The presence of oxygen in aerated solution upon irradiation tends to produce reactive oxygen species, e.g., O 2 −• (Adegboyega et al 2016;Ranjan and Ramalingam 2016;Rong et al 2019). However, the produced reactive oxygen species may interact with released metal ions to reproduce silver nanoparticles in a feedback mechanism (He et al 2011).…”

Food and Beverage Ingredients Induce the Formation of Silver Nanoparticles in Products Stored within Nanotechnology-Enabled Packaging

“…Also, light exposure, temperature, reducing agent concentration, and the broader food system formulation were highlighted as important mediators of the final AgNP quantity and form (see Figure S7 and associated discussion in the Supporting Information). Light has been implicated in both AgNP formation 67 and dissolution, 68 which may be why light exposure enhanced AgNP-derived color changes in some beverages but diminished them in others (Figure S7). It is reasonable to expect that these factors will also influence reformation of AgNPs in foods stored within AgNP/LDPE packaging.…”

Photochemical Behavior of Microbial Extracellular Polymeric Substances in the Aquatic Environment

“…Owing to the absorption of photons, DOM could be photoactivated to form its triplet-excited-state DOM ( 3 DOM*), which is one of the important sources for the further generation of reactive radical species, such as hydroxyl radicals ( • OH) and singlet oxygen ( 1 O 2 ). − The potential photoactivity of DOM provides new insights into the process of natural carbon circulation, yet the photochemical behaviors of EPS and their environmental implications are largely uncharacterized in spite of the fact that EPS is a main DOM discharged into the waterbody from wastewater utilities. As one of the most active moieties in EPS, humic substances have been shown to be susceptible to natural sunlight. − Attempts have been made to investigate the effects of EPS on the valence alternation of metal ions. For instance, the positive effects of EPS on silver nanoparticle formation from Ag + have been shown to occur under both visible-light and ultraviolet irradiation .…”