title: Sunlight-driven reduction of silver ions by natural organic matter: formation and transformation of silver nanoparticles.
abstract: Photobiogeochemical reactions involving metal species can be a source of naturally occurring nanoscale materials in the aquatic environment. This study demonstrates that, under simulated sunlight exposure, ionic Ag is photoreduced in river water or synthetic natural water samples that contain natural organic matter (NOM), forming Ag nanoparticles (AgNPs) that transform in size and shape and precipitate out upon extended irradiation. We show that the dissolved oxygen concentration does not appear to affect AgNP formation rates, indicating that reactive transients such as superoxide, hydrated electron, and triplet NOM do not play a large role. By varying pH and NOM concentrations and adding competing cations on the AgNP formation, we present three lines of evidence to show that Ag ion photoreduction likely involves ionic Ag binding to NOM. Our work suggests that photochemical reactions involving ionic Ag and NOM can be a source of nanosized Ag in the environment.
authors.affiliation: National Research Council Associate, National Exposure Research Laboratory, Ecosystems Research Division, United States Environmental Protection Agency, Athens, Georgia 30605, USA. whou0603@gmail.com
authors.forename: Wen-Che
authors.initials: WC
authors.lastname: Hou
authors.forename: Brittany
authors.initials: B
authors.lastname: Stuart
authors.forename: Roberta
authors.initials: R
authors.lastname: Howes
authors.forename: Richard G
authors.initials: RG
authors.lastname: Zepp
mesh_terms: D002412:Cations; D006863:Hydrogen-Ion Concentration; D053768:Metal Nanoparticles; D010084:Oxidation-Reduction; D012834:Silver / Q000737:chemistry*; D013472:Sunlight
chemical_list: D002412:Cations; D012834:Silver