Environmental Engineering Reference
In-Depth Information
- Precipitation and flocculation of the NMs 01
- Hydrophobic interactions, sequestration, ion
transfer, coordination reactions or covalent bond fonnationof NMs
with soil or sediment organic matter
- Diffusion of NMs into mineral or organic matter micropores
Dissolution/Precipitation
Dissolution of NMs in water until limited by their solubility For
instance, solubilization of individual Cso through light- or bio-
activated fimctionalizationof Go in nature
Abiotic Transformation-Hydrolysis
- Cleavage of the molecules of NMs into smaller, more wateisoluble portions and in
the formation of new C-OH or C-H bonds via acid-catalyzed, alkaline, and neutral
hydrolysis. Under abiotic conditions, environmental factorssuch as pH, temperature,
dissolved organic matter, dissolved metal ions or other inorganic matters (e.g., N0,
O?), etc., may impact the level of hydrolysis.
Volatilizaion and Absorption
- Transfer of NMs from either a liquid or a solid phase to a
gas phase (volatilization) or a gas phase to the liquid phase
(absorption)
Abiotic Transformation- RedoxReactions
- Redox transformation of certain organic and metallic NMsunder either aerobic or
anaerobic conditions. For instance,
naeromc conditions. ±-or instance,
KV +2.82 Fe° + 0.75 Fe^ + 2.25 HaO -> Ntt" + 1.19 FeO + 0.50 OH
• Fe° + 3& + 2 KO -> 4 y-FeOOH
Physical adsorption: Van der Waals' forces and electrostatic
interactions between the NMs in solution and the cell walls of
the microorganisms
Ion exchange: The polysaccharides associated with microbial
cell walls allow exchange of bivalent metal ions for the counter
ions of the polysaccharides, resulting in the biosorptive uptakeof
heavy metals that may be released by the NMs
Complexation Complex fonnationof NMs with amino and
carboxyl groups found m cell wall polysaccharides
Precipitation Tthe microorganism produces compounds that
enhance the precipitation of the NM or its intermediate both in
the solution and on the cell surface
Abiotic Transformation-Photocatalyzed Reactions
- Photochemical dissolution of Ag NPs was observed by repetitive laser pulses or
when photoejected electrons were scavenged byspecies such as N?O
- Photocatalytic reactions associated with different NMsfor different purposes, such
as photocatalytic degradation of contaminants with NPs disinfection of water or
wastewater, cytotoxicity of NMs, etc. In most of these reactions, light irradiated
NMs exhibits strong activity because of releasing of some free radicals.
- Direct photolysis: Photodegradation processes involving direct light absorption by
the NMs followed by one of many decomposition mechanisms
Bioaccumulation
A net result of competing processes of uptake and
elimination
Bioaccumulation can be affected by many factors,
including biological factors of aquatic biota, the
physical, chemical, and biological characteristics
of NMs, and environmental conditions
Biotramformation
- Transformation of NMs by nicroorganisms or higher plants]
the terms of degradation, mineralization, detoxification, and
others (e.g., activation or methylationlthrough metabolic
reactions such as oxidation, reduction, hydrolysis, and
synthetic reactions
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