Agriculture Reference
In-Depth Information
wards water and the hydrated radii of the particles were much higher than
their un-hydrated counterparts. Therefore it is very important to get stable
suspension of nano-particles of desired size for harnessing the benefit of
nano-particles.
The zeta potential of the nano-particles is another important param-
eter that has been extensively investigated for stability of nano-particles.
High zeta potential (negative or positive) will impart stability to the nano-
particles suspension, whereas nano-particles with low zeta potentials tend
the zeta potential of nano-particles. When pH is at point of zero charge
(
pzc
) or isoelectric point, the nano-particles exhibit minimum stability
(i.e., exhibit maximum coagulation/flocculation). When the pH is lower
than the
pzc
value, the nano-particle surface is positively charged and the
zata potential will increase with decreasing pH below the
pzc
. Conversely,
at pH above
pzc
, the surface is negatively charged and the zeta potential
will be more negative with increasing pH. The values of
pzc
of selected
rounding aqueous medium is also an important factor affecting the sta-
bility of the nano-particles. When ionic strength is increased and/or the
zeta potential is reduced (both effects usually result from an increased salt
concentration), attractive force between colloids will outweigh the repul-
sion, and the particles can then adhere each time they collide. The surface
charge is also another important property that can dominance the migra-
tion of ENMs in porous media (Darlington et al., 2009). The soil particles
are generally negatively charged. Thus, positively charge ENMs will be
readily electro-statically attracted to the soil surface. Nano-particles with
higher negative charges are believed more mobile in soil matrix because of
the longer electrostatic repulsion between the nano-particles and soil par-
ticles and between nano-particles themselves as well. Therefore, various
methods have been applied to modify ENM surface properties to control
(enhance or restrict) the transport of ENMs in porous media/soil among
which surface functionalization with hydrophilic functional groups (e.g.,
-OH and -COOH) and surface physical modification using polymers or
surfactants are two commonly adopted methods.
