70
L. J. Rather et al.
ENM. The surface-modified particles have higher resistance to the light penetration
efficiency which reduces the excitation or photodegradation. The rate of photochemical transformation depends upon the rate determining step which is the mass transfer
from material surface to the exterior media. Photoactivation of TiO 2 has been found
to have profound effects on its binding with the dissolved organic matter [127].
5.2 Oxidation and Reduction
The substances in a particular oxidation states are subjected to reduction or oxidation processes if they are thermodynamically favorable [128]. Redox reactions are
influenced by various factors including the pH, occurrence of reducing or oxidizing
agents and presence of stabilizers on the ENM surfaces which will decrease the rate
of transformation [129].
5.3 Dissolution
Dissolution refers to the release of water-soluble separate ions/molecules [130–132].
The dissolution involves the reaction of molecules on the surface and the release of the
ionic forms or direct solubilization of the component materials, tracked by diffusional
passage [133].
5.4 Precipitation
Precipitation occurs under certain conditions in presence of precipitating agents
in which new solid materials are formed from the solutions (suspended materials
from solutions) [119, 134]. The precipitation is governed by the precipitation laws
involving the solubility product (Ksp) and ionic product (K w ) under equilibrium
conditions, which in turn depends upon the ionic strength, ligand availability, pH,
and temperature of the media [128]. The existence of adsorbed materials may increase
or decrease the rate of dissolution by surface protection phenomenon which can be
further confirmed by thermodynamic calculations. However, slow diffusion rates
may delay in the achievement of the final product [135–137].
L. J. Rather et al.
ENM. The surface-modified particles have higher resistance to the light penetration
efficiency which reduces the excitation or photodegradation. The rate of photochemical transformation depends upon the rate determining step which is the mass transfer
from material surface to the exterior media. Photoactivation of TiO 2 has been found
to have profound effects on its binding with the dissolved organic matter [127].
5.2 Oxidation and Reduction
The substances in a particular oxidation states are subjected to reduction or oxidation processes if they are thermodynamically favorable [128]. Redox reactions are
influenced by various factors including the pH, occurrence of reducing or oxidizing
agents and presence of stabilizers on the ENM surfaces which will decrease the rate
of transformation [129].
5.3 Dissolution
Dissolution refers to the release of water-soluble separate ions/molecules [130–132].
The dissolution involves the reaction of molecules on the surface and the release of the
ionic forms or direct solubilization of the component materials, tracked by diffusional
passage [133].
5.4 Precipitation
Precipitation occurs under certain conditions in presence of precipitating agents
in which new solid materials are formed from the solutions (suspended materials
from solutions) [119, 134]. The precipitation is governed by the precipitation laws
involving the solubility product (Ksp) and ionic product (K w ) under equilibrium
conditions, which in turn depends upon the ionic strength, ligand availability, pH,
and temperature of the media [128]. The existence of adsorbed materials may increase
or decrease the rate of dissolution by surface protection phenomenon which can be
further confirmed by thermodynamic calculations. However, slow diffusion rates
may delay in the achievement of the final product [135–137].