title: Effects of humic substances on precipitation and aggregation of zinc sulfide nanoparticles.
abstract: Nanoparticulate metal sulfides such as ZnS can influence the transport and bioavailability of pollutant metals in anaerobic environments. The aim of this work was to investigate how the composition of dissolved natural organic matter (NOM) influences the stability of zinc sulfide nanoparticles as they nucleate and aggregate in water with dissolved NOM. We compared NOM fractions that were isolated from several surface waters and represented a range of characteristics including molecular weight, type of carbon, and ligand density. Dynamic light scattering was employed to monitor the growth and aggregation of Zn-S-NOM nanoparticles in supersaturated solutions containing dissolved aquatic humic substances. The NOM was observed to reduce particle growth rates, depending on solution variables such as type and concentration of NOM, monovalent electrolyte concentration, and pH. The rates of growth increased with increasing ionic strength, indicating that observed growth rates primarily represented aggregation of charged Zn-S-NOM particles. Furthermore, the observed rates decreased with increasing molecular weight and aromatic content of the NOM fractions, while carboxylate and reduced sulfur content had little effect. Differences between NOM were likely due to properties that increased electrosteric hindrances for aggregation. Overall, results of this study suggest that the composition and source of NOM are key factors that contribute to the stabilization and persistence of zinc sulfide nanoparticles in the aquatic environment.
authors.affiliation: Department of Civil and Environmental Engineering, Duke University , Box 90287, Durham, North Carolina 27708, United States.
authors.forename: Amrika
authors.initials: A
authors.lastname: Deonarine
authors.forename: Boris L T
authors.initials: BL
authors.lastname: Lau
authors.forename: George R
authors.initials: GR
authors.lastname: Aiken
authors.forename: Joseph N
authors.initials: JN
authors.lastname: Ryan
authors.forename: Heileen
authors.initials: H
authors.lastname: Hsu-Kim
mesh_terms: D011232:Chemical Precipitation; D004785:Environmental Pollutants / Q000737:chemistry*; D006812:Humic Substances; D053768:Metal Nanoparticles / Q000737:chemistry*; D008970:Molecular Weight; D009994:Osmolar Concentration; D013440:Sulfides / Q000737:chemistry*; D014867:Water / Q000737:chemistry; D017967:Zinc Compounds / Q000737:chemistry*
chemical_list: D004785:Environmental Pollutants; D006812:Humic Substances; D013440:Sulfides; D017967:Zinc Compounds; D014867:Water; C031238:zinc sulfide