Page 334 - Environmental Nanotechnology Applications and Impacts of Nanomaterials

Nanomaterials for Groundwater Remediation 319

Figure 8.11 Surface coatings may prevent interactions between nanoparticles and
bacteria or mineral grains. Polyelectrolytes provide electrosteric repulsive forces,
while polymers provide steric repulsive forces. Short chain anionic or cationic sur-
factants can provide electrostatic repulsive or attractive forces.

charged functional groups (anionic or cationic) and provide electros-
teric repulsions. Surfactants can provide electrostatic repulsive or
attractive forces (depending on their charge), but are less effective
than polymers or polyelectrolytes because their small size is unsuit-
able for steric repulsions. Polymers adsorb strongly (effectively irre-
versible) to nanoparticles, while surfactant adsorption is more easily
reversible (Braem et al. 2003; Fleer et al. 1993; Holmberg et al. 2003;

TABLE 8.2 Coatings from Each Class to Be Evaluated
Stabilization
Coating Charge type Relevance

Polymers Common nontoxic polymer used to
Polyethylene glycol Nonionic Steric stabilize NP dispersions. Adsorbed
(PEG) PVA reduces bacterial adsorption to
Polyvinyl alcohol Nonionic Steric surfaces (Koziarz and Yamazaki 1999).
(PVA) Cellulose is used to prepare
Carboxymethyl Nonionic Steric stabilized nanoiron dispersions
cellulose (He and Zhao 2005). Inexpensive
and biodegradable.
Guargum Nonionic Steric
Polyelectrolytes Used to prepare stabile nanoiron
Triblock copolymers Anionic Electrosteric dispersions that partition to the TCE/
(PMAA x -PMMA y - water interface (Saleh et al. 2005a).
PSS z ) PSS homopolymer is a common
Polystyrene Anionic Electrosteric inexpensive alternative used to
sulfonate stabilize NPdispersions. Polylysine is
Poly(aspartic acid) Anioinc Electrostatic a biodegradable polypeptide and
bactericidal (Roddick-Lanzilotta and
McQuillan 1999). Poly(aspartic acid)
should be biodegradable and less
bactericidal.
Surfactants SDBS is a common anionic surfactant
SDBS Anionic Electrostatic shown to enhance nanoiron mobility
Alkyl Nonionic Steric/ (Saleh et al. 2007) but resists
polyglucosides Hydration biodegradation. Alkyl polyglucosides
are biodegradable (Matsson
et al. 2004).