Aggregation Kinetics of Citrate and Polyvinylpyrrolidone Coated Silver Nanoparticles in Monovalent and Divalent Electrolyte Solutions

Abstract

The aggregation kinetics of silver nanoparticles (AgNPs) that were coated with two commonly used capping agents—citrate and polyvinylpyrrolidone (PVP)—were investigated. Time-resolved dynamic light scattering (DLS) was employed to measure the aggregation kinetics of the AgNPs over a range of monovalent and divalent electrolyte concentrations. The aggregation behavior of citrate-coated AgNPs in NaCl was in excellent agreement with the predictions based on Derjaguin–Landau–Verwey–Overbeek (DLVO) theory, and the Hamaker constant of citrate-coated AgNPs in aqueous solutions was derived to be 3.7 × 10-20 J. Divalent electrolytes were more efficient in destabilizing the citrate-coated AgNPs, as indicated by the considerably lower critical coagulation concentrations (2.1 mM CaCl2 and 2.7 mM MgCl2 vs. 47.6 mM NaCl). The PVP-coated AgNPs were significantly more stable than citrate-coated AgNPs in both NaCl and CaCl2, which is likely due to steric repulsion imparted by the large, non-charged polymers. The addition of humic acid resulted in the adsorption of the macromolecules on both citrate- and PVP-coated AgNPs. The adsorption of humic acid induced additional electrosteric repulsion that elevated the stability of both nanoparticles in suspensions containing NaCl or low concentrations of CaCl2. Conversely, enhanced aggregation occurred for both nanoparticles at high CaCl2 concentrations due to interparticle bridging by humic acid clusters.

Particle Coating-Dependent Interaction of Molecular Weight Fractionated Natural Organic Matter: Impacts on the Aggregation of Silver Nanoparticles

“…This suggested that electrostatic interaction play important role in the stabilization of PVP-, Cit-and BareAgNPs. 21 The CCCs, derived by intersection of extrapolations through both regimes, 21 in NaClO 4 solutions, were 447.27, 109.68, and 8.10 mmol L −1 for PVP-, Cit-, and Bare-AgNPs, respectively. The CCCs in Ca(ClO 4 ) 2 solutions were 15.56, 1.51, and 1.06 mmol L −1 for of PVP-, Cit-and Bare-AgNPs, respectively.…”

“…The negative charge of PVP-AgNPs possibly origins from the adsorption of the residual side products on AgNPs. 21 Similarly, the negative charge of Bare-AgNPs possibly origins from the adsorption of borate, the decomposition product from KBH 4 . As shown by the zeta-potentials, the better stability of PVPAgNPs than that of Cit-AgNPs cannot be explained only by electrostatic interaction.…”

“…The inhibition of aggregation by >100 kDa NOM should be ascribed to the steric repulsion provided by adsorbed NOM, whereas the enhancement of aggregation by high MW M f -NOM (>100 kDa and 30−100 kDa NOM) in the presence of high concentration of Ca 2+ was ascribed to the interparticle bridging of NOM. 21 Bare-AgNP. The aggregation of Bare-AgNPs in both monoand divalent electrolytes was significantly inhibited by pristine NOM ( Figure 5).…”

“…The PVP content in PVP-AgNP suspension was measured by a Teledyne Tekmar TOC analyzer according to literature. 21 The AgNP solution was also characterized by X-ray photoelectron spectroscopy (XPS). For XPS analysis, the solution was dropped on Si wafer and dried in the vacuum desiccators at room temperature.…”

Retention and Remobilization of Stabilized Silver Nanoparticles in an Undisturbed Loamy Sand Soil

“…In addition, the presence of different electrolyte types, which generally occurs in soils, has been proven to play an important role in NP stability and mobility in porous media. 7,22,23 In particular, divalent cations can enhance aggregation and deposition in comparison to monovalent ions. 6,24 The environmental fate of silver nanoparticles (AgNPs) is of special concern because of their strong antimicrobial activity, and considerable amounts of research have therefore addressed this issue.…”