Deposition of Silver Nanoparticles in Geochemically Heterogeneous Porous Media: Predicting Particle Mobility From Surface Composition Analysis

Abstract

<p>This study focused on the effect of surface heterogeneity on the affinity of the nanoparticle (for that surface) and the viability of using surface composition analysis to facilitate the prediction of such affinity. The transport of the uncoated silver nanoparticles (AgNPs) in a porous medium composed of silica glass beads partially covered with iron oxide (hematite) was studied and compared to that in a porous medium composed of unmodified glass beads (GB). It was found that at relative high pH (8.3) there existed only a small difference in AgNPs mobility in both porous media unless the ionic strength was sufficiently high while at lower pH (5) AgNPs had considerably lower affinity for the GB collectors compared to that of the iron oxide coated glass beads (FeO-GB) collectors, even at relative low ionic strengths. There was a linear correlation between the average nanoparticle affinity for media composed of mixtures of FeO-GB and GB collectors and the relative composition of those media as quantified by the attachment efficiency over a range of mixing mass ratios of the two types of collectors, so that the average AgNPs affinity for these media is readily predicted from the mass (or surface) weighted average of affinities for each of the surface types. Using X-ray Photoelectron Spectroscopy (XPS) to quantify the</p><p>composition of the collector surface appears to be a viable means to predict the affinity between the nanoparticles and a collector surface with known composition provided that a relevant correlation curve could be established from measured affinity between the nanoparticles and collector surfaces with similar but different composition (i.e. surfaces with the same components but different proportion of each component).</p>