This title appears in the Scientific Report : 2014 

Transport and Retention of Stabilized Silver Nanoparticles in Porous Media
Liang, Yan (Corresponding Author)
Agrosphäre; IBG-3
Jülich Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag 2014
IV, 109 S.
Dissertation, RWTH Aachen, 2014
Dissertation / PhD Thesis
Terrestrial Systems: From Observation to Prediction
Modelling and Monitoring Terrestrial Systems: Methods and Technologies
Schriften des Forschungszentrums Jülich Reihe Energie & Umwelt / Energy & Environment 212
Please use the identifier: in citations.
Due to the widespread application of silver nanoparticles (AgNPs) and the resulting potential exposure in the environment, information about their environmental transport and fate is essential for risk assessment. AgNPs are commonly modified with functional groups, surfactants, or polymers to increase their stability in liquids and the surface modification greatly influences the environmental behavior of AgNPs. The aim of this study is therefore to investigate the transport and retention of surfactant-stabilized AgNPs under environmentally relevant conditions. Experiments were conducted with water-saturated columns packed with quartz sand, around 90% water-saturated columns filled with undisturbed loamy sand soil, and a lysimeter. Inductively coupled plasma-mass spectrometry/optical emission spectrometry (ICP-MS/OES) was used to analyze the concentrations of AgNPs, Ca$^{2+}$ , K+, Fe, and Al. The experimental breakthrough curves (BTCs) and retention profiles (RPs) from column experiments were described using a numerical model that considers time- and depth-dependent retention. Column experiments with quartz sand packing were also conducted in the presence of surfactant to deduce the influence of surfactant on AgNP transport, especially on the spatial distribution of retained AgNPs that determines the long-term transport potential. In addition, to better understand the interactions of AgNPs and the matrix in the environment, remobilization of retained AgNPs from undisturbed soil was studied by changing the solution chemistry such as change of cation types and ionic strength reduction. Experimental results showed that the normalized concentration in BTCs for AgNPs obtained from water-saturated columns increased with a decrease in solution ionic strength (IS), and an increase in flow velocity ($\textit{q}$), sand grain size, and input concentration (C$_{o}$). In contrast to the conventional filtration theory, RPs in sand exhibited uniform, nonmonotonic, or hyperexponential shapes that were sensitive to physicochemical conditions. The simulated retention rate coefficient (k$_{1}$) and maximum retained concentration on the solid phase (S$_{max}$) increased with IS and as the grain size and/or C$_{o}$ decreased. The RPs were more hyperexponential in finer textured sand and at lower C$_{o}$ because of their higher values of S$_{max}$, which indicated a larger retention capacity of the porous media. Conversely, RPs were nonmonotonic or uniform at higher C$_{o}$ and in coarser sand that had lower values of S$_{max}$, and tended to exhibit higher peak concentrations in the RPs at lower flow velocities and at higher solution IS. These observations indicate that uniform and nonmonotonic RPs occurred under conditions when S$_{max}$ was filled. The sensitivity of the nonmonotonic RPs to IS and flow velocity in coarser textured sand indicates that AgNPs were partially interacting in a secondary energy minimum according to the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. However, elimination of the secondary minimum only produced recovery of a small portion (<10%) of the retained AgNPs. These results imply that AgNPs were largely irreversibly interacting in a primary minimum associated with microscopic heterogeneity of the porous [...]