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 colloidal stability of AgNPs in contact with 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 colloid suspensions with well-characterized particle size distributions (5-50 nm). The AgNP suspensions were then reacted with MnO2 and natural organic matter in batch reactions followed by analysis with several techniques including X-ray absorption spectroscopy (EXAFS and XANES), X-ray photoelectron spectroscopy (XPS), scanning and transmission electron microscopy, and micro-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. Micro-Raman imaging analysis of AgNP colloid 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.

Investigation of silver nanoparticle interactions with manganese dioxide using x-ray spectroscopic and microscopic techniques

251st National Meeting (2016)

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