Page 340 - Environmental Nanotechnology Applications and Impacts of Nanomaterials

Nanomaterials for Groundwater Remediation 325

Targeting approaches
There are several potential approaches to achieve contaminant target-
ing. The first approach is to impart to the particles some affinity for the
specific contaminant of interest. This targeted delivery approach is
inspired by targeted drug delivery technology—localizing the remedia-
tion agents (the “drug”) at the contaminant source (the “diseased tissue”)
via “smart” thermodynamic interactions between the particles and the
contaminant. This approach has been recently evaluated in the labora-
tory (Saleh et al. 2005a; Saleh et al. 2005b; Saleh et al. 2007). Saleh
et al. (2005) used multifunctional triblock copolymers (Figure 8.15)
adsorbed to the nanoiron particles to disperse nanoiron into water for
good aquifer transportability, minimize undesirable adhesion to mineral
and natural organic matter (NOM) surfaces, and preferentially anchor
nanoiron at the DNAPL/water interface for source-zone accumulation
(Figure 8.16) (Saleh et al. 2005a). The multifunctional polymer assem-
blies adsorbed on the nanoiron surfaces present hydrophilic blocks that
form stable nanoparticle suspensions in water, a requirement for even-
tual subsurface delivery. The hydrophilic blocks are strong polyanions,
so they repel the predominantly negatively charged surfaces of miner-
als, NOM, and NOM-coated minerals that would be encountered in soils
(Beckett and Le 1990; Day et al. 1994). When in contact with DNAPL,
hydrophobic polymer blocks respond by anchoring the nanoparticle at
the DNAPL/aqueous interface (Figure 8.16).
The affinity of the triblock copolymer modified nanoiron has been
examined in the laboratory. RNIP interfacial anchorage by the same
polymers that promoted their transport through sand columns was
demonstrated by the ability of modified nanoiron to stabilize TCE-in-water

Figure 8.15 Hydrophobic-hydrophilic
triblock copolymers containing a short
PMAA anchoring group (left), PMMA
hydrophobic block (middle), and a
hydrophilic sulfonated polystyrene
block (right).