The stability of silver nanoparticles (AgNPs) in contact with soil and reactive soil minerals is an area of considerable interest and may play a strong role in the fate and transport of AgNPs in the environment. The objective of this study was to determine the chemical and colloid stability of AgNPs in contact with metal oxides such as manganese dioxide (MnO2), a natural soil mineral oxidant. Laboratory-synthesized AgNPs were purified, size-selected, and concentrated by a tangential flow filtration method to remove Ag+ ions and produce AgNP suspensions with well-characterized particle size distributions (5-50 nm). The AgNP suspensions were then reacted with a variety of soil materials such as MnO2 and natural organic matter in batch reactions. The AgNP mineral suspensions were then analyzed by several techniques including X-ray absorption spectroscopy (EXAFS and XANES), scanning and transmission electron microscopy, and Raman scattering. The analysis of MnO2 mineral-treated AgNP by XANES showed that AgNP oxidation occurred in the presence of MnO2 and produced Ag+ ion. Raman analysis of reacted AgNP reacted with MnO2 exhibited trace occurrences of Ag-O vibrational stretches indicating possible Ag+ adsorption to Ag oxide surfaces. This study revealed that soil mineralogy and MnO2 concentration are important factors that partially govern the fate and transport of AgNP in soil and groundwater.

Silver nanoparticle stability and oxidative dissolution by metal oxide soil minerals

2019 Spring National Meeting

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