Key Factors Controlling the Transport of Silver Nanoparticles in Porous Media

Abstract

The current study investigated the mobility of four silver nanoparticles (AgNPs) stabilized using different capping agents and represent the common stabilization mechanisms as well as surface charging scenarios in reactive and nonreactive porous media. The AgNPs were (1) uncoated H2-AgNPs (electrostatically stabilized) and (2) citrate coated AgNPs (Citrate-AgNPs) (electrostatically stabilized), (3) polyvinylpyrrolidone coated AgNPs (PVP-AgNPs) (sterically stabilized), and (4) branched polyethyleneimine coated AgNPs (BPEI-AgNPs) (electrosterically stabilized). The porous media were (1) quartz sand (QS), (2) ferrihydrite-coated sand (FcS), and (3) kaolin-coated sand (KcS). The H2-AgNPs and Citrate-AgNPs were readily mobile in QS but significantly retained in FcS and KcS with more deposition achieved in the KcS media. The deposition of the H2-AgNPs and Citrate-AgNPs followed the order of KcS > FcS > QS. The PVP-AgNPs breakthrough occurred more rapid as compared to the H2-AgNPs and Citrate-AgNPs but the deposition of PVP-AgNPs followed the same order of the electrostatically stabilized AgNPs (KcS > FcS > QS). The BPEI-AgNPs were readily mobile regardless of the porous media reactivity. Physicochemical interactions were the dominant filtration mechanism in the majority of the investigated cases but straining played the major role in the deposition of the electrostatically stabilized H2-AgNPs and Citrate-AgNPs in the KcS media. The results highlight the importance of both the stabilization mechanism and capping agent chemistry as key factors governing the transport of AgNPs in the environment.

Transport of silver nanoparticles in intact columns of calcareous soils: The role of flow conditions and soil texture

“…For example, the retention of NPs may occur even under unfavorable conditions for attachment due to local surface charge heterogeneities (Lin et al, 2011), aggregation (Bradford et al, 2006), and straining in small pores and at locations of high surface roughness (Kasel et al, 2013a). Additionally, an increase in the NPs transport due to stabilizing agents causing short-range repulsive forces (El Badawy et al, 2013), retarded and asymmetric BTCs, and uniform, non-monotonic, and hyperexponential retention profiles (RPs) (Liang et al, 2013a) are examples of violations of the filtration theory.…”

“…Most researchers have studied the transport of AgNPs in highly idealized systems consisting of repacked, homogeneous, coarse-textured porous media (e.g., glass beads, quartz sands) under water-saturated or unsaturated conditions (e.g., El Badawy et al, 2013;Fang et al, 2013;Liang et al, 2013b). While these studies have provided valuable insights into the mechanisms controlling the transport of AgNPs, they do not exactly resemble natural soil conditions.…”

Modeling the effects of water velocity on TiO2 nanoparticles transport in saturated porous media

“…According to previous studies, the presence of surfactants, natural organic matter and bacteria can modify the interactions between NP and porous media, resulting in a reduction of NP retention (Chen et al, 2012;Chowdhury et al, 2012;Godinez and Darnault, 2011;Godinez et al, 2013;Wang et al, 2012). For more complex porous media, columns of soil (Cornelis et al, 2013;Fang et al, 2009;Liang et al, 2013a) and sand with reactive coatings (El Badawy et al, 2013;Wang et al, 2012) have been used. It was found that TiO 2 NPs are more retained in soils with a high clay content and strong salinity.…”

“…One way to evaluate retention mechanism effects is to apply filtration theory (El Badawy et al, 2013;Li et al, 2011;Petosa et al, 2012), which takes into account physicochemical conditions and describes the frequency of collisions between nanoparticles and collector grains. The parameters of filtration theory offer a simple description of deposition dynamics but can be quite imprecise in some cases.…”

Suspended particle transport through constriction channel with Brownian motion

“…There are many situations where small objects subject to Brownian motion in a fluid are introduced to the constriction of microscopic channels, for example, filtration of colloidal particles through porous media [1][2][3], translocation of DNA molecules through nanopore sequencers [4][5][6][7][8][9][10][11][12][13][14][15][16][17], and lab-on-achip (LOC) devices where analytes are introduced to various domains of nano-and microchannels for analysis [18][19][20][21][22][23][24][25]. It is now well known that the translocation phenomena of polymer molecules through nanopores with a diameter comparable to the monomer size have stochastic nature [5,6].…”