Challenges in Groundwater Remediation with Iron Nanoparticles: Enabling Colloidal Stability - Nanotechnologies for Water Environment Applications - page 202

Surface Coating of nZVI. An aqueous slurry of nZVI was combined with a 10
gL -1 APGC solution. The mixture was sonicated for 30 min followed by gentle end-
over-end rotation for 72 h to disperse the nanoparticles to allow the polymer to absorb
onto the surface of the nanoparticles. The APGC-coated nZVI were then filtered and
washed multiple times to remove any excess non-adsorbed APGC.

Sedimentation Rate Measurements. The colloidal stability of the APGC-coated
nZVI was evaluated by measuring sedimentation rates of nanoparticle suspensions using
a UV-spectrometer. The optical density at a wavelength of 508 nm was monitored over
several hours to determine sedimentation rate (Krajangpan et al., 2008).

8.3.4 Results and Discussion

nZVI Synthesis and Characterization. nZVI particles were synthesized
following the method enumerated earlier. The average particle diameter was determined
to be approximately 35 nm with a particle size range between 10 and 90 nm (Table 8.1).
Similar particle sizes have been reported by Li et al. (2006). A thin (2-5 nm) oxide shell
was identified around the nZVI, which was believed to be created during particle
passivation process. A similar core-shell structure has been reported by others (Nurmi et
al., 2005; Li et al., 2006; Martin et al., 2008). The shell has been reported to be made of
iron oxide/hydroxide and the core, zero-valent iron (Nurmi et al., 2005; Li et al., 2006).
Recently, Martin et al. (2008) reported that nZVI (50-100 nm) are always surrounded by
a thin shell/layer of an amorphous material. They reported it to be FeOOH. The FeOOH
layer thickness was found to be 2-4 nm. The BET surface area of the nZVI synthesized
during this experiment was found to be 25 m 2 g -1 which is in agreement with others (22
m 2 g -1 reported by Ponder et al., 2000; 36 m 2 g -1 reported by Liu et al., 2005).
Table 8.1 Particle size distribution of nZVI synthesized.
Particle Size (diameter, d)
(nm)

Percent Present
(%)

Cumulative Percentage
(%)

0 < d < 10 0.00 0.00

10 < d < 20 11.22 11.22

20 < d < 30 34.15 45.37

30 < d < 40 25.37 70.73

40 < d <50 13.66 84.39

50 < d < 60 9.27 93.66

60 < d < 70 4.39 98.05

70 < d < 80 1.46 99.51

80 < d < 90 0.49 100.00

90 < d < 100 0.00 100.00

d > 100 0.00 100.00