Laboratory-synthesized silver nanoparticles (AgNP) were reacted with several soil minerals including aluminosilicate clays (montmorillonite, kaolinite), metal oxides (Al, Fe, Mn, and Ti), gypsum, and silica sand in the presence and absence of natural organic matter (NOM). The objective of this study was to determine the stability of AgNP in contact with common soil components to identify mineral phases and NOM conditions where oxidative transformation occurs. The synthetic AgNP were purified by a tangential flow filtration method that allowed control over particle size distribution and AgNP suspension density. The soil mineral- and NOM-treated AgNP samples were analyzed by several techniques such as X-ray absorption spectroscopy (EXAFS and XANES), X-ray photoelectron spectroscopy (XPS), scanning and transmission electron microscopy, and Raman scattering. The analysis of soil mineral-treated AgNP by XANES showed that Ag oxidation occurred in the presence of MnO<sub>2</sub> and TiO<sub>2</sub> metal oxides with formation of Ag oxide phase. It was found that NOM forms surface-complexed species with AgNPs mainly through the ionized carboxylic moieties located in the immediate vicinity of the metallic nanosurface, and the interaction becomes stronger with the increase in incubation time. The fluorescence emission spectra confirmed the Raman/SERS observations of significant fluorescence quenching upon the AgNP addition and the formation of AgNP-NOM-AgNP aggregates, which may decrease AgNP mobility during their groundwater transport. This study revealed that soil mineral composition and NOM content are important properties that partially govern the fate and transport of AgNP in soil and groundwater.

Spectroscopic and microscopic investigation of soil mineral and natural organic matter-treated silver nanoparticles

249th National Meeting (2015)

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