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Roles of Silver–Chloride Complexations in Sunlight-Driven Formation of Silver Nanoparticles
Citation:
Singh, A., W. Hou, T. Lin, AND R. Zepp. Roles of Silver–Chloride Complexations in Sunlight-Driven Formation of Silver Nanoparticles. ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 53(19):11162-11169, (2019). https://doi.org/10.1021/acs.est.9b02115
Impact/Purpose:
The unique physical and chemical properties of silver nanoparticles (AgNPs) drive their increasing commercial uses including antibacterial products. According to the nanotechnology inventory from the 2018 Woodrow Wilson Database, almost 24% of current consumer products contain AgNPs. Several studies indicate that heavy use of AgNPs could result in their dispersion into aquatic environments where they pose a potential threat to aquatic biota and humans. A majority of AgNPs in consumer products are eventually released into sewer systems then into wastewater treatment systems where they are released into aquatic environments. The silver nanoparticles undergo transformations in the environment through changes in aggregation state, oxidation state, precipitation of secondary phases, or sorption of organic species. These transformations can result in the formation of new species that potentially have toxic effects which have yet to be fully examined. In aerobic natural surface water, silver ion (Ag+) exists in various Ag+-Cl- complexes due to a strong affinity for chloride ion (Cl-); however, little information is available about the role of the Ag+-Cl- complex in the formation of silver nanoparticles (AgNPs). This study demonstrates that soluble AgClx(x−1)− species act as a precursor of AgNPs under simulated sunlight irradiation. Silver nanoparticles are regulated by EPA's Office of Pesticide Programs (OPP). OPP is currently conducting a review of AgNPs so the results of this study may provide useful inputs to this review.
Description:
In aerobic natural surface water, silver ion (Ag+) exists in various Ag+-Cl- complexes due to a strong affinity for chloride ion (Cl-); however, little information is available about the role of the Ag+-Cl- complex in the formation of silver nanoparticles (AgNPs). This study demonstrates that soluble AgClx(x−1)− species act as a precursor of AgNPs under simulated sunlight irradiation. The AgNP photoproduction increases with Cl- levels up to 0.0025 M ([Ag+] = 5 × 10-7 M), and decreases with continued Cl- level increase (0.09 M to 0.5 M). At [Cl-] ≤ 0.0025 M (freshwater systems), photoproduction of AgNP correlates with the formation of AgCl(aq), suggesting that it is the most photoactive species in those systems. Matching the ionic strength of experiments containing various Cl- levels indicate that the trend in AgNP photoproduction correlates with Cl- concentrations rather than ionic strength induced effects. The photoproduction of AgNPs is highly pH-dependent, especially at pH > 8.3. The UV and visible light portions of the solar light spectrum are equally important in photoreduction of Ag+. Overall, we show evidence that AgClx(x−1)− species irradiated under sunlight conditions contributes to formation of nanosized silver (Ag) in the environment.
URLs/Downloads:
DOI: Roles of Silver–Chloride Complexations in Sunlight-Driven Formation of Silver Nanoparticles