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Fate of Silver Nanoparticles in Surface Water Environments

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2011, Doctor of Philosophy, Ohio State University, Civil Engineering.

The widespread use of nanomaterials has the potential to adversely affect human and ecosystem health. Silver nanoparticles, as the most mass produced and utilized nanomaterials, may be released from the washing of silver-containing fabrics and food through sewage systems to natural waters. However, the fate of silver nanoparticles after entering the water environment is not clearly known. The objectives of the research were to: 1) evaluate how water chemistry, particularly concentration and valence of electrolyte, and dissolved natural organic matter affect the aggregation of silver nanoparticles, 2) elucidate how the physical and chemical properties of the silver nanoparticles, altered through the addition of different capping layers, affects their aggregation, and 3) investigate how aggregation, capping layer and environmentally-related factors, mainly sunlight irradiation affect silver release from silver nanoparticles in natural water.

To meet these objectives, a systematic investigation of the aggregation behavior and silver release of a suite of silver nanoparticles in a controlled laboratory setting was conducted. The early stage aggregation kinetics of bare silver nanoparticles (ca. 82 nm in diameter), as well as particles coated with a suite of stabilizing agents (Citrate, SDS and Tween) were investigated over a range of electrolyte types (NaCl, NaNO3 and CaCl2) and concentrations by monitoring time-rate of change of the particle hydrodynamic radius using dynamic light scattering (DLS). The electrophoretic mobility and morphologies of particles and aggregates were evaluated. Experiments were also carried out in the presence of Nordic aquatic fulvic acid to investigate the effect of NOM on the stability of silver nanoparticles. To investigate silver release from silver nanoparticles under environmentally relevant conditions, batch experiments were conducted with bare and coated silver nanoparticles in a natural water in the presence and absence of synthetic sunlight irradiation.

The aggregation kinetic results of uncoated silver nanoparticles were consistent with classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, although immediate dissolutions of particles were observed in all three electrolyte solutions. The dissolution of the silver nanoparticles was highly dependent on the electrolyte type and concentration. Secondary AgCl precipitates formed within the chloride-containing systems as the particles dissolved during aggregation. Aggregation of the silver nanoparticles was also examined in the presence of 10 mg l-1 Nordic aquatic fulvic acid and was little changed compared to that evaluated under identical fulvic acid-free conditions.

The aggregation of citrate-coated particles and SDS-coated particles were very similar to that for the uncoated particles. The non-ionic steric stabilizer, Tween, significantly enhanced stability. The dissolution of the silver nanoparticles was inhibited by the SDS and Tween coatings, but not by the citrate coating. The behavior of the Tween-coated silver nanoparticles also exhibited a dependence on electrolyte type, as its stability was greater and dissolution was lower in NaNO3 than in NaCl.

In the natural water system investigated, Tween-coated particles released silver quicker than did bare- and citrate-coated particles, which rapidly aggregated. A silver concentration of 40 µg/L was reached after just 6 hours by Tween-coated particles, accounting for ca. 3 % of the total silver. The similar levels of silver concentrations were reached in uncoated and Citrate-coated systems at the end of the 15 days. The presence of synthetic sun light and citrate impart significant morphological changes to the particles, however, aggregation seems the controlling process in this study.

John Lenhart, PhD (Advisor)
Harold Walker, PhD (Committee Member)
Linda Weavers, PhD (Committee Member)
Nicholas Basta, PhD (Committee Member)
179 p.

Recommended Citations

Citations

  • Li, X. (2011). Fate of Silver Nanoparticles in Surface Water Environments [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1320888780

    APA Style (7th edition)

  • Li, Xuan. Fate of Silver Nanoparticles in Surface Water Environments. 2011. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1320888780.

    MLA Style (8th edition)

  • Li, Xuan. "Fate of Silver Nanoparticles in Surface Water Environments." Doctoral dissertation, Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1320888780

    Chicago Manual of Style (17th edition)