Journal of Nanoparticle Research

, Volume 10, Issue 5, pp 795–814 | Cite as

Stabilization of aqueous nanoscale zerovalent iron dispersions by anionic polyelectrolytes: adsorbed anionic polyelectrolyte layer properties and their effect on aggregation and sedimentation

  • Tanapon Phenrat
  • Navid Saleh
  • Kevin Sirk
  • Hye-Jin Kim
  • Robert D. Tilton
  • Gregory V. LowryEmail author
Research Paper


Nanoscale zerovalent iron (NZVI) particles are 5–40 nm sized Fe0/Fe-oxide particles that rapidly transform many environmental contaminants to benign products and are a promising in situ remediation agent. Rapid aggregation and limited mobility in water-saturated porous media limits the ability to deliver NZVI dispersions in the subsurface. This study prepares stable NZVI dispersions through physisorption of commercially available anionic polyelectrolytes, characterizes the adsorbed polymer layer, and correlates the polymer coating properties with the ability to prevent rapid aggregation and sedimentation of NZVI dispersions. Poly(styrene sulfonate) with molecular weights of 70 k and 1,000 k g/mol (PSS70K and PSS1M), carboxymethyl cellulose with molecular weights of 90 k and 700 k g/mol (CMC90K and CMC700K), and polyaspartate with molecular weights of 2.5 k and 10 k g/mol (PAP2.5K and 10K) were compared. Particle size distributions were determined by dynamic light scattering during aggregation. The order of effectiveness to prevent rapid aggregation and stabilize the dispersions was PSS70K(83%) > ≈PAP10K(82%) > PAP2.5K(72%) > CMC700K(52%), where stability is defined operationally as the volume percent of particles that do not aggregate after 1 h. CMC90K and PSS1M could not stabilize RNIP relative to bare RNIP. A similar trend was observed for their ability to prevent sedimentation, with 40, 34, 32, 20, and 5 wt%, of the PSS70K, PAP10K, PAP2.5K, CMC700K, and CMC90K modified NZVI remaining suspended after 7 h of quiescent settling, respectively. The stable fractions with respect to both aggregation and sedimentation correlate well with the adsorbed polyelectrolyte mass and thickness of the adsorbed polyelectrolyte layers as determined by Oshima’s soft particle theory. A fraction of the particles cannot be stabilized by any modifier and rapidly agglomerates to micron sized aggregates, as is also observed for unmodified NZVI. This non-dispersible fraction is attributed to strong magnetic attractions among the larger particles present in the polydisperse NZVI slurry, as the magnetic attractive forces increase as r6.


NZVI Nanoscale zerovalent iron particles Polyelectrolyte Dispersion stability Colloid Surface modification Aggregation and sedimentation Steric stabilization Extended DLVO Environmental nanotechnology Groundwater remediation Nanoparticle environmental fate and transport 



Nanoscale zerovalent iron


Poly(styrene sulfonate)


Carboxymethyl cellulose






Reactive nano-scale iron particles


Dynamic light scattering



This research was funded in part by the Department of Defense through the Strategic Environmental Research and Development Program (W912HQ-06-C-0038), the Office of Science (BER), U.S. Department of Energy, (DE-FG07-02ER63507), the U.S. EPA (R830898), the U.S. National Science Foundation (BES-0608646), and the Royal Thai Government through a fellowship to Tanapon Phenrat.


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Copyright information

© Springer Science+Business Media B.V. 2007

Authors and Affiliations

  • Tanapon Phenrat
    • 1
  • Navid Saleh
    • 1
  • Kevin Sirk
    • 2
  • Hye-Jin Kim
    • 1
  • Robert D. Tilton
    • 2
    • 3
  • Gregory V. Lowry
    • 1
    • 2
    Email author
  1. 1.Department of Civil & Environmental EngineeringCarnegie Mellon UniversityPittsburghUSA
  2. 2.Department of Chemical EngineeringCarnegie Mellon UniversityPittsburghUSA
  3. 3.Department of Biomedical EngineeringCarnegie Mellon UniversityPittsburghUSA

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