Effect of Adsorbed Polyelectrolytes on Nanoscale Zero Valent Iron Particle Attachment to Soil Surface Models

Abstract

Polyelectrolyte coatings significantly increase the mobility of nanoscale zerovalent iron (NZVI) in saturated porous media. The effect can be attributed to improved colloidal stability of NZVI suspensions, decreased adhesion to soil surfaces, or a combination of the two effects. This research explicitly examines how coatings control NZVI adhesion to model soil surfaces. NZVI was coated with three different polyeleotrolyte block copolymers based on poly(methacrylic acid), poly(methyl methacrylate or butyl methacrylate), and poly(styrenesulfonate) or with a poly(styrenesulfonate) homopolymer. SiO2 and a humic acid film served as model soil surfaces. The polyelectrolytes increased the magnitude of the electrophoretic mobility of NZVI over a broad pH range relative to unmodified NZVI and shifted the isoelectric point outside the typical groundwater pH range. Quartz crystal microgravimetry measurements indicated extensive adhesion of unmodified NZVI to SiO2. Polyelectrolyte coatings decreased adhesion by approximately 3 orders of magnitude. Adding 50 mM NaCL to screen electrostatic repulsions did not significantly increase adhesion of modified NZVI. Coated NZVI did not adhere to humic acid films for either 1 mM NaHCO3 or 1 mM NaHCO3 + 50 mM NaCl. The lack of adhesion even in a high ionic strength medium was attributed to electrosteric repulsion, as opposed to electrostatic double layer repulsion, between the polyelectrolyte-coated NZVI and the negatively charged surfaces. The lack of significant adhesion on either model surface was observed for all polymer architectures investigated.

Emerging patterns for engineered nanomaterials in the environment: a review of fate and toxicity studies

“…Adsorbing charged ions such as pyrophosphate onto the surface of TiO 2 NPs stabilizes the NPs and decreases aggregation (Jiang et al 2009a, b). Polyelectrolyte surface coatings can be used to inhibit nZVI aggregation and enhance mobility Sirk et al 2009). The stabilizers not only affect the behavior of the NP within a product but can also enhance the mobility of ENMs in the environment (Tungittiplakorn et al 2004).…”

A Comparison Between Field Applications of Nano-, Micro-, and Millimetric Zero-Valent Iron for the Remediation of Contaminated Aquifers

“…This is due to the complexity and numerousness of phenomena involved, such as: the magnetic properties of iron nanoparticles (Hong et al 2009), particle attachment to soil surface as a function of surface coatings (Sirk et al 2009), the possible desorption of the same particles once settled and adhered to porous media ), and the increase in mobility in the presence of natural organic matter (Johnson et al 2009). Moreover, some phenomena which take place in the field are hardly reproducible in laboratory tests.…”

Assessing the colloidal properties of engineered nanoparticles in water: case studies from fullerene C60 nanoparticles and carbon nanotubes

“…Usually, the flow chambers of the QCM use much simpler geometries, such as in radial stagnation point and parallel-plate flow systems. To date, the QCM has been used to study the deposition of fullerene C 60 nanoparticles, [113,118] titanium dioxide nanoparticles, [119] quantum dots, [120] viruses, [121] and ZVI nanoparticles [122,123] on silica surfaces.…”