Impacts of Morphology, Natural Organic Matter, Cations, and Ionic Strength on Sulfidation of Silver Nanowires

Silver nanowires (AgNWs) are being widely utilized in an increasing number of consumer products, which could release silver to aquatic environments during the use or washing process, and have received growing concerns on their potential risks to bio-organisms and humans. The present study demonstrated that AgNWs mainly experienced direct oxysulfidation by reacting with dissolved sulfide species (initial S^2- concentration at 1.6 mg/L) to produce silver sulfide nanostructures under environmentally relevant conditions. Granular Ag₂S nanoparticles were formed on the surface of the nanowires. The sulfidation rate constant (k_Ag) of AgNWs was compared with those of silver nanoparticles (AgNPs) at different particle sizes. It was found that the k_Ag positively correlated with the specific surface areas of the silver nanomaterials. Natural organic matter (NOM) suppressed the sulfidation of AgNWs to different extents depending on its concentration. Divalent cations (Mg²⁺ and Ca²⁺ ions) substantially accelerated the sulfidation rates of AgNWs compared to monovalent cations (Na⁺ and K⁺ ions). At the same ionic strengths, Ca²⁺ ions displayed the highest promoting effect among the four metallic ions.