Dynamic exchange between Ag+ and Ag0: Implications for the environmental fate of Ag nanoparticles

The environmental transformation and fate of nanomaterials are critical for their consequences. Although Ag nanoparticles (Ag NPs) are frequently detected in the environment, their transformation and fate, particularly in relation to sediment or mineral surfaces, remain poorly understood. In this study, we investigated the behaviors of Ag NPs on γ-Al 2 O 3 , a model mineral, under environmentally relevant aqueous conditions. We discovered that Ag NPs gradually diminished during light irradiation, ultimately transforming into ultrasmall NPs, clusters, and single atoms. The newly formed secondary Ag 0 on the surface of γ-Al 2 O 3 exhibited low sunlight absorption but high dissolution activity. A chemical equilibration was established quickly between Ag + in the solution bulk and Ag 0 on the γ-Al 2 O 3 surfaces, but dynamic exchange between Ag + and Ag 0 continued to evolve Ag 0 speciation afterwards. Light drove these processes, with O 2 involved. The dynamic exchange persisted continuously, although its rate could be influenced by environmental parameters. Synopsis In a simulated environmental photochemical process, Ag 0 and Ag + undergo rapid dynamic exchange, leading to the downsizing of Ag nanoparticles on γ-Al 2 O 3 surfaces into ultrasmall nanoparticles, clusters, and single atoms.