Sulfidation of silver nanoparticles (AgNPs) is likely to occur during transport through wastewater infrastructure, which will alter AgNP reactivity. In this study, arrays of immobilized AgNPs fabricated by nanosphere lithography (NSL) were used to study the mechanism of AgNP sulfidation and the stability of the resultant particles. The characteristic NSL pattern was discernible by atomic force microscopy and transmission electron microscopy following exposures to Na2S solutions and raw sewage sludge, and the mean AgNP height increased in both cases. Measured Ag:S atomic ratios were consistent with near complete conversion to Ag2S in Na2S solutions, yet only partial conversion in sludge. The crystal structure of the mineral form of Ag2S was detected in the nanoparticles following the exposures. Dissolution rates in NaCl solutions following 0-30 min exposures to 1 mM Na2S progressively decreased with increasing sulfidation time until they were not statistically significant. Similarly, AgNP dissolution rates were not significant in specimens that were exposed to sludge for 6 d. These results imply that sulfidation can mitigate AgNP toxicity by preventing Ag+ release; however, sulfidation does not proceed uniformly, so the potential for silver dissolution and toxicity is not completely eliminated unless sulfidation is complete. The ability of our methodology to provide a detailed characterization of AgNP transformations in complex mixtures is promising for understanding nanomaterial behavior in natural systems.

Controlled evaluation of silver nanoparticle sulfidation: Reaction mechanism and particle stability

248th National Meeting (2014)

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