Nanoparticles for Treatment of Arsenic - Nanotechnologies for Water Environment Applications - page 121

The experimental potential curves suggest that the electrolyte ions are
indifferent and the affinity of K + and NO 3 - to the surface is equal, otherwise, the IEP
would be different from the PZC (Rudzinski et al., 1992). There is a clear trend showing
that the absolute value became lower with increasing ionic strength as a result of
decreased double layer thickness (Figure 5.3).
5.3.2 Effect of Anatase Size on Removal of Arsenate

A number of batch adsorption tests were performed, in which samples of
nanocrystalline anatase products having different primary crystallite diameters were
used to remove arsenate from spiked tap water samples. The data from these tests were
analyzed to correlate the degree of arsenate removal with the primary crystallite
diameter of the anatase sample. As shown in Figure 5.4, the degree of removal was
highest for samples of anatase having the smallest primary crystallite diameters (6.6 nm)
and lowest for samples of anatase having the largest primary crystallite diameters (134
nm).

80 76

60 56

40

24

20

4

0

6.6 15 20 134

Primary anatase particle size (nm)

Figure 5.4 Arsenate removal efficiency as a function of primary anatase particle size.
5.3.3 Effect of Drying Temperature on TiO 2 Size and Arsenate Removal
Capacity

A number of samples of nanocrystalline anatase product were prepared at
different drying temperatures and tested for their effectiveness in removing arsenate
from spiked tap water samples. Figure 5.5 illustrates the relationship of the drying
temperature to the primary crystallite diameter of the anatase crystals and to the degree
of arsenate removal demonstrated in the batch adsorption tests. Drying the anatase