Evidence for the critical role of nanoscale surface roughness on the retention and release of silver nanoparticles in porous media

Abstract

Although nanoscale surface roughness has been theoretically demonstrated to be a crucial factor in the interaction of colloids and surfaces, little experimental research has investigated the influence of roughness on colloid or silver nanoparticle (AgNP) retention and release in porous media. This study experimentally examined AgNP retention and release using two sands with very different surface roughness properties over a range of solution pH and/or ionic strength (IS). AgNP transport was greatly enhanced on the relatively smooth sand in comparison to the rougher sand, at higher pH, and lower IS and fitted model parameters showed systematic changes with these physicochemical factors. Complete release of the retained AgNPs was observed from the relatively smooth sand when the solution IS was decreased from 40 mM NaCl to deionized (DI) water and then the solution pH was increased from 6.5 to 10. Conversely, less than 40% of the retained AgNPs was released in similar processes from the rougher sand. These observations were explained by differences in the surface roughness of the two sands which altered the energy barrier height and the depth of the primary minimum with solution chemistry. Limited numbers of AgNPs apparently interacted in reversible, shallow primary minima on the smoother sand, which is consistent with the predicted influence of a small roughness fraction (e.g., pillar) on interaction energies. Conversely, larger numbers of AgNPs interacted in deeper primary minima on the rougher sand, which is consistent with the predicted influence at concave locations. These findings highlight the importance of surface roughness and indicate that variations in sand surface roughness can greatly change the sensitivity of nanoparticle transport to physicochemical factors such as IS and pH due to the alteration of interaction energy and thus can strongly influence nanoparticle mobility in the environment.

Colloid Interaction Energies for Surfaces with Steric Effects and Incompressible and/or Compressible Roughness

“…14−16 In addition, interaction energies have frequently been demonstrated to be highly dependent on the incompressible nanoscale roughness proper- ties of both surfaces. 17 In particular, small amounts of incompressible nanoscale roughness protrusions that are specific to a colloid or porous medium 9,14,15,17,18 have been shown to dramatically decrease the magnitudes of the primary minimum, energy barrier height, and the secondary minimum, 19−29 especially when nanoscale roughness occurs on both interacting surfaces. 12,30 Furthermore, the influence of incompressible nanoscale roughness will change with the solution chemistry, the colloid size, the surface charges, and the water velocity.…”

“…Incompressible nanoscale roughness on mineral and metal surfaces will reduce colloid mass transfer to this surface by increasing the hydrodynamic slip. − In addition, interaction energies have frequently been demonstrated to be highly dependent on the incompressible nanoscale roughness properties of both surfaces . In particular, small amounts of incompressible nanoscale roughness protrusions that are specific to a colloid or porous medium ,,,, have been shown to dramatically decrease the magnitudes of the primary minimum, energy barrier height, and the secondary minimum, − especially when nanoscale roughness occurs on both interacting surfaces. , Furthermore, the influence of incompressible nanoscale roughness will change with the solution chemistry, the colloid size, the surface charges, and the water velocity. ,,, Theoretical calculations have demonstrated that specific incompressible nanoscale roughness properties can greatly diminish colloid retention and aggregation, even when interactions for smooth surfaces are predicted to be favorable. , Spatial variability of incompressible roughness properties can explain why limited amounts of colloid aggregation and retention can occur. ,, …”

Nanomaterials for subsurface application: study of particles retention in porous media

“…Although several researches have been done for the evaluation of functionalized NPs transport through porous media, but there is no consensus among researchers regarding the effect of rock properties on the efficiency of NPs transport. It has been long recognized that the mineralogy and surface structure of rocks significantly could affect the efficiency of NPs and chemical flooding (Arsalan et al 2015;Liang et al 2020). Therefore, the effect of physicochemical properties of porous media on the retention of functionalized NPs in pore walls must be considered while designing the process.…”

Mobility of Cellulose Nanocrystals in Porous Media: Effects of Ionic Strength, Iron Oxides, and Soil Colloids

“…Natural soils are very different from model porous media (e.g., quartz sand) in terms of soil solution chemistry, metal oxides, and soil colloids. The mechanisms that these factors influence the transport of nanoparticles through porous media have been well-documented [38,39]. The retention of nanoparticles in secondary energy minima on soil surfaces is enhanced at higher ionic strength because the secondary minimum depth increases with increasing ionic strength [40,41].…”