Environmental Engineering Reference
In-Depth Information
aid of organic solvents, which has significant implications for the transport of these
materials in the environment (Brant et al., 2005).
Water soluble NM derivatives are essential for many emerging biomedical
technologies that exploit the unique chemical properties and physical structure of NMs.
It has been reported that nanoscale aggregates of Ceo (referred to here as n-Ceo) are a
result of pristine Ceo (either in solid state or liquid solution) that contact with water.
Rather than completely precipitating, some Ceo form suspended and water-stable
aggregates up to a concentration of 100 ppm. Andrievshy et al. (2002) studied two types
of fullerene-water colloidal systems; molecular-colloidal Ceo solution in water (CeoFWS)
and typical monodisperse Ceo hydrosol were compared in their work. It was confirmed
that CeoFWS consists of isolated Ceo molecules in hydrated state, Ceo@{H2O}«, and of
their small spherical Ceo clusters of different sizes. It was shown that CeoFWS
simultaneously has the properties of both true solutions and colloidal systems.
Solubility of NMs is a critical factor when the cytotoxicity of these NMs needs to be
considered. Sayes et al. (2004) confirmed that the aggregates are the lethal species,
while more highly soluble fullerenes have less pronounced biological effects, which
partially confirmed their hypothesis: sparingly soluble fullerenes will cause oxidative
damage to cellular membranes even at relatively low concentrations, and that the
resulting toxicity will diminish as the fullerene cage becomes more fully derivatized and
water soluble. Covalent bonds made to the pristine cage of Ceo may result in NMs with
varying levels of water solubility as high as 13000-100000 mg/L (Sayes et al., 2004).
The solubility of NMs may be modified by surface functionalization of veracious NMs.
NMs can also partially dissolve into the solution. Cadmium selenide (CdSe) core
QDs were found acutely toxic under certain conditions because of the liberation of free
Cd + ions due to deterioration of the CdSe lattice. Moreover, the cytotoxicity of QDs
was modulated by processing parameters during synthesis, exposure to ultraviolet light,
and surface coatings. When appropriately coated, CdSe-core QDs can be rendered
nontoxic and used to track cell migration and reorganization in vitro (Derfus et al.,
15.3.3 Volatilization and Absorption
Due to their small particle sizes, NM diffusion, caused by a chemical potential
between the phases, may transfer NMs from either a liquid or a solid phase to a gas
phase (referred to as volatilization) or a gas phase to the liquid phase (referred to as
absorption). The mathematical description of volatilization and absorption are the same
as eq. 15.45. When volatilization needs to be considered, "- RU" needs to be added to
eq. 15.13, while for absorption, "+ RIT" needs to be added.
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