title: Interactions of aqueous Ag+ with fulvic acids: mechanisms of silver nanoparticle formation and investigation of stability.
abstract: This study investigated the possible natural formation of silver nanoparticles (AgNPs) in Ag(+)-fulvic acid (FA) solutions under various environmentally relevant conditions (temperature, pH, and UV light). Increase in temperature (24-90 °C) and pH (6.1-9.0) of Ag(+)-Suwannee River fulvic acid (SRFA) solutions accelerated the appearance of the characteristic surface plasmon resonance (SPR) of AgNPs. The rate of AgNP formation via reduction of Ag(+) in the presence of different FAs (SRFA, Pahokee Peat fulvic acid, PPFA, Nordic lake fulvic acid, NLFA) and Suwannee River humic acid (SRHA) followed the order NLFA > SRHA > PPFA > SRFA. This order was found to be related to the free radical content of the acids, which was consistent with the proposed mechanism. The same order of AgNP growth was seen upon UV light illumination of Ag(+)-FA and Ag(+)-HA mixtures in moderately hard reconstituted water (MHRW). Stability studies of AgNPs, formed from the interactions of Ag(+)-SRFA, over a period of several months showed that these AgNPs were highly stable with SPR peak reductions of only ~15%. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) measurements revealed bimodal particle size distributions of aged AgNPs. The stable AgNPs formed through the reduction of Ag(+) by fulvic and humic acid fractions of natural organic matter in the environment may be transported over significant distances and might also influence the overall bioavailability and ecotoxicity of AgNPs.
authors.affiliation: Chemistry Department, Florida Institute of Technology, 150 West University Boulevard, Melbourne, Florida 32901, USA.
authors.forename: Nathaniel F
authors.initials: NF
authors.lastname: Adegboyega
authors.forename: Virender K
authors.initials: VK
authors.lastname: Sharma
authors.forename: Karolina
authors.initials: K
authors.lastname: Siskova
authors.forename: Radek
authors.initials: R
authors.lastname: Zbořil
authors.forename: Mary
authors.initials: M
authors.lastname: Sohn
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Schultz
authors.forename: Sarbajit
authors.initials: S
authors.lastname: Banerjee
mesh_terms: D001578:Benzopyrans / Q000737:chemistry*; D006812:Humic Substances / Q000032:analysis; D006863:Hydrogen-Ion Concentration; D053758:Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure; D010084:Oxidation-Reduction; D045483:Rivers / Q000737:chemistry; D012834:Silver / Q000737:chemistry*; D013696:Temperature; D014466:Ultraviolet Rays
chemical_list: D001578:Benzopyrans; D006812:Humic Substances; D012834:Silver; C005023:fulvic acid