Environmental Engineering Reference
In-Depth Information
TABLE 2.3
Diffusion Coeficients ( D × 10 5 cm 2 /s) Measured during Drug Release from Hydrogels
and Nanocomposites at 20°C
Hydrogel
Ribolavin
Methyl Orange
Propranolol
Tryptophan
PNIPAM/PANI
1.12
0.21
0.72
1.12
PNIPAM/PMANI
0.61
0.32
-
9.52
PNIPAM-co-2% AMPS/PANI
-
-
1.24
0.16
PNIPAM-co-2% AMPS/PMANI
0.61
0.21
0.02
1.12
observed while at the same time the partition of other molecules (e.g., methyl orange) is
small (<50). Therefore, it is possible to selectively remove some solutes in the presence of
a large concentration of others. This is important when a contaminant has to be removed
from a nutritive solution or toxic solutes (ammonia, nitrite) have to be removed from
aquarium water without removing nutrients. Both processes are relevant in aquaculture.
Moreover, these gels can be used to selectively remove toxic solutes to improve the sensi-
tivity of analytical techniques, in a special case of solid-phase preconcentration [138].
2.3.8 Diffusion Coefficient of Solutes in Hydrogels
To load toxic solutes from water, not only the partition coeficient should be high but also
the mass transport rate should be fast enough to establish the equilibrium in a reasonable
time. In the absence of electric ields, there is no migration. Since in solids convection is
impossible, the only driving force is the concentration gradient that gives rise to diffusion.
The diffusion coeficients of different molecules in hydrogel-based nanocomposites show
values quite close to those in water; however, there is some inluence in the interaction
between the solute and the matrix (Table 2.3).
Unfortunately, the same kind of interactions that increase the partition coeficient seems
to decrease the diffusion coeficient.
2.4 How to Use Nanoporous Materials for Aquananotechnology
Different applications of nanoporous materials and nanocomposites in aquananotechnology
will be described.
2.4.1 Removal of Toxic Ions by EDI
Organic dyes are widely used in textile and food industries. About 15% of the total world
production of dyes is lost during the dyeing process and is released in the textile efluents
[139]. The release of those colored wastewaters in the ecosystem is a dramatic source of
unsightly pollution, eutrophication, and perturbations in the aquatic life. Different tech-
nological systems for the removal of dyes have been developed, such as adsorption [140],
biological [141], chemical [142], or photochemical degradation [143]. An alternative way to
remove ions from solution involves EDI [144] (Scheme 2.8).
 
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