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Nanoparticle Transport, Aggregation, and Deposition 253
0,25
16
pH = 3 (a)
pH = 7 14
0,2
12
0,15 10
% vol 8
0,1 % vol
6
4
0,05
2
0 0
0,001 0,01 0,1 1 10 100 1000
Hydrodynamic diameter (micron)
500
(b)
400
300
a p (nm)
200
100
0
4 5 6 7 8 9 10 11 12
pH
Figure 7.11 The pH-dependence of the nano-Fe 2 O 3 size distribution
a) without and b) with a DMSA coating procedure [1].
aggregation of the 6 nm particles, and the measured size is approximately
450 ± 20 nm. For pH > 8.5, the DMSAgenerates enough negative surface
charge to enhance the stability of the suspension, and the maghemite
nanoparticles are well dispersed as small aggregates with an average
size of 20 ± 1 nm at pH 11. Once these modified maghemite nanopar-
ticles are exposed to a solution pH > 8.5 they are capable of maintain-
ing a stable suspension and do not aggregate even when the pH is
reduced to the acidic range [1].
