Fate and Transport of Nanomaterials in Aquatic Environments - Nanotechnologies for Water Environment Applications - page 540

is possible to prepare tailored, multifunctional polymeric materials using a cost effective,
synthetic route to modify NMs for different applications (which is the main concept of
green nanotechnology). However, very limited information is available on the fate and
transport of these/-NMs in the environment, which justifies more research in the future.
15.5.3Interactions between NMs and Contaminants/Environments
There are four common types of engineered NMs: carbon-based materials (e.g.,
fullerenes, and nanotubes), dendrimers (nanosized polymers built from branched units),
metal-based materials (e.g., metal oxides, QDs, nanogold, nanosilver) and composites
(combination of NPs with other NPs or with larger, bulk-type materials). Of these four
common types of engineered NMs, previous studies have mainly focused on metal-
based materials (e.g., iron oxides, titanium dioxide) and a few carbon NMs (e.g., nano-
Ceo) for their performance in remediation of environmental pollutants and their fate and
transport in the environment (Goodman et al., 2001; Zhang, 2003; Joo and Cheng, 2006;
USEPA, 2007). In environmental areas, the popular NMs include metal or transition
metal oxides (e.g., NZNI, nano-FesCU, TiO2, ZnO, MgO, CaO, A^Os) and nanoscale
bimetallic particles (e.g., Pd/Fe, Pd/Mg, Pt/Zn where Fe or Zn serving primarily as
electron donor + Pd, Pt as a catalyst) (Therese and Kamath, 2000; Caruso et al., 2001;
Zhang, 2003; Lowry and Johnson, 2004; Liu, et al., 2005; Nurmi et al., 2005; Giasuddin
et al., 2007). When NMs are used in the area of environmental engineering and
sciences, several questions about NM-induced chemical interactions need to be
answered, such as how do nanosized adsorbents and chemicals sorbed to them influence
their respective environmental interactions? Can NMs alter the mobility and the
reactivity of other substances in the environment? Previous studies have demonstrated
several important things:
(1) NMs can alter the partitioning behavior of chemicals between environmental
compartments and between the environment and living organisms. As mentioned
before, NMs can be functionalized with different chemicals, polymers or metal
oxides (see Section 15.5.2); the/-NMs have different morphologies, structures, and
amounts of functional groups on their surface, and consequently, their behavior (e.g.,
for adsorption, removal of pollutants), interactions with the environment (e.g.,
change the pH or redox in the surrounding area) and contaminants (e.g., electron
static interaction, sorption-precipitation, ion exchange on the NM's surface) are
different. For example, protons compete with cations for binding sites on NMs (e.g.,
/-CNTs). The MWCNTs of Ba 2+ -ALG/MWCNT composite adsorbents [MWCNTs
encapsulated in cross-linked alginate (ALG) microvesicles] carries negative charges
on its surface. The cage restricts the access of anions of large molecular weights,
such as humic acids, because of electrostatic repulsion. The cage also restricts the
access of colloids of larger sizes, because of size exclusion. Ionic dyes partition into
the cage and then are captured by MWCNTs probably on the basis of van der Waals