The concentration of Ag NPs in environmental media limits the ionic release kinetics, hence the transformation and stability of Ag NPs is also influenced. The transformations of Ag NP at environmental realistic concentration (ERC) ≤ µg/L may differ from that reported at higher concentration (e.g. mg/L). Analytical techniques characterizing NPs at µg/L have advantages and limitations, including the inherent bias regarding theoretical and analytical considerations. In this work, we applied the nanoparticle tracking analysis (NTA), the single particle ICP-MS, the localized surface plasmon resonance (LSPR) analysis and the diagrams of predominant species to study the stability, dissolution and transformation of Ag NPs at ERC in presence of NOM, Cl-, S2-, PO43-, NH4+, and in a model wastewater. The influence of nominal sizes of Ag NPs (20, 40, 80 and 100 nm) on their aggregation and dissolution in wastewater were also studied. The results showed that NTA was a suitable technique for sizing Ag NPs, especially for those smaller than 60 nm that the sp-ICP-MS could not effectively size in wastewater. However, sp-ICP-MS was useful to determine the coexisting of Ag+ and Ag0 at nanoscale. The particles with larger nominal size were more stable as determined by LSPR. The formation of Ag2S(s) and AgCl(s), and soluble species as AgClx(x-1)-, AgNH3+and Ag(NH3)2+ were estimated when Ag+ is released and concentration of major ions is known. Stable size and dissolution of Ag NPs at ERCs were observed in presence of NOM (5-800 µg/L) and PO43- (9.5-47.5 mg/L) while higher dissolution and precipitation were the dominant process in the media containing either Cl-(0.07-10.64 g/L), S2-(0.32-32.1 mg/L) or NH4+ (36-90 mg/L), respectively. The aggregation and dissolution of Ag NPs in model wastewater were observed for all nominal sizes, aggregates ranged from 135 to 240 nm and dissolution ranged from 20.8 to 34.5 % for all sizes after 5 h of exposition. This study filled the data gap of the environmental behavior and fate of Ag NPs at environmental realistic concentration, and could provide fundamental knowledge for its environmental risk assessment.

Multi-technique approach to study the stability of silver nanoparticles at environmental realistic concentrations in aqueous media

2019 Fall National Meeting

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