Rethinking Stability of Silver Sulfide Nanoparticles (Ag₂S-NPs) in the Aquatic Environment: Photoinduced Transformation of Ag₂S-NPs in the Presence of Fe(III)

Abstract

ABSTRACT:The stability of engineered nanomaterials in a natural aquatic environment has drawn much attention over the past few years. Silver sulfide nanoparticles (Ag 2 S-NPs) are generally assumed to be stable in a natural environment as a result of their physicochemical property; however, it may vary depending upon environmental conditions. Here, we investigated whether and how the environmentally relevant factors including light irradiation, solution pH, inorganic salts, dissolved organic matter (DOM), and dissolved oxygen (DO) individually and in combination influenced the stability of Ag 2 S-NPs in an aquatic environment. We presented for the first time that transformation of Ag 2 S-NPs can indeed occur in the aqueous system with an environmentally relevant concentration of Fe 3+ under simulated solar irradiation and natural sunlight within a short time (96 h), along with significant changes in morphology and dissolution. The photoinduced transformation of Ag 2 S-NPs in the presence of Fe 3+ can be dramatically influenced by solution pH, Ca 2+ /Na + , Cl − /SO 4 2− , DOM, and DO. Moreover, Ag 2 S-NP dissolution increased within 28 h, followed rapid decline in the next 68 h, which may be a result of the reconstitution of small Ag 2 S-NPs. Taken together, this work is of importance to comprehensively evaluate the stability of Ag 2 S-NPs in an aquatic environment, improving our understanding of their potential risks to human and environmental health.

Formation of Nanosilver from Silver Sulfide Nanoparticles in Natural Waters by Photoinduced Fe(II, III) Redox Cycling

“…Its pathway is not currently understood, but may be related to the formation of Fe 2 S 3 that tends to be unstable and decomposes to FeS, 42,44 followed by the second CER between FeS and the released silver ions to reform Ag 2 SNPs. 21 When the CERs maintain an equilibrium within a short time, the concentration of silver ions remains constant.…”

Quantifying the Sensitivity of Soil Microbial Communities to Silver Sulfide Nanoparticles Using Metagenome Sequencing

“…As a potential positive, in these experiments, Ag 2 S-NPs were shown to be less toxic than pristine AgNPs and Ag + . However, it has been shown that in aquatic environments, the potential exists for Ag 2 S-NPs to act as a slow-release form of toxic Ag + [8]. Overall, this lack of information prevents the development of threshold values to quantify the risks of Ag-based NPs to soil microorganisms and hence, the ability to develop regulatory Soil Quality Guidelines (SQGs) to protect soil ecosystems.…”

An investigation into the effects of silver nanoparticles on natural microbial communities in two freshwater sediments

“…Herein, partial transformation of the AgNPs to Ag 2 S can be expected with the relatively low molar ratio of AVS/Ag, and the existence form of Ag 2 S was likely to be Ag(0)/Ag 2 S coreÀshell particles. Ag 2 S-NPs was recently reported to have a chance to dissolve into ionic silver in the aquatic system with low concentration of Fe 3þ under simulated solar irradiation (Li et al, 2016), thereby indicating the potential toxicity of Ag 2 S to microorganisms. Nevertheless, in most cases, Ag 2 S-NPs were demonstrated to be stable and remained constant for a long time and sulfidation was deemed as natural antidote for AgNPs Sekine et al, 2015).…”