Page 344 - Environmental Nanotechnology Applications and Impacts of Nanomaterials

Nanomaterials for Groundwater Remediation 329

Figure 8.18 Trajectories of polymer-coated nanoiron in an etched silica micromodel con-
taining water and partial TCE saturation. Particles tended to migrate toward the
TCE/water interface as the approach velocity decreased. Trajectory points are 300 ms
apart (Baumann et al. 2005).

time of 1 to 10 seconds), particles tended to flow past entrapped TCE
rather than migrate to the interface (Figure 8.18).
Even though emulsification occurs under high shear conditions that
of course are far removed from aquifer conditions, preliminary experi-
ments in sand-packed columns and dodecane-coated sand-packed
columns indicate some potential for in situ targeting as long as adequate
time is available for nanoparticles to diffuse to the NAPL/water inter-
face. Sand column transport studies conducted with NAPL-coated sand,
under flow conditions similar to the clean sand experiments described
above, indicated a 10 percent reduction in elution for PMAA 42 -PMMA 26 -
PSS 466 -coated RNIP compared to the clean sand column (Saleh et al.
2007). To achieve this, however, the flow had to be stopped for 24 hours
to allow time for the particles to transport to the interface. Surface mod-
ifications that impart more hydophobicity to the particle should provide
better NAPL targeting. Using a higher hydrophobe/hydrophile ratio, or
changing the middle hydrophobic block from methyl-methacrylate to
butyl-methacrylate to lower the glass transition temperature and thus
promote swelling of the hydrophobe in contact with NAPL may further
enhance targeting. These targeting experiments indicate potential for
in situ targeting, but additional research to optimize the block size and
type and hydrophile/hydrophobe ratio are needed.