Environmental Engineering Reference
In-Depth Information
higher than in thin films of the same materials. The smaller the particles, the
higher the absorption efficiency.
3. Uniformity. Clusters, aggregates or filaments, in other words, the molecular or
atomic assemblies that form nanoparticles, are defined by the interaction of
forces among the molecules or atoms of a particle and the interaction forces
among particles.
4. Functionalisation. Nanoparticles of any type can be linked to microbiological
entities randomly, through natural processes occurring in atmosphere, water or
at the surface of the Earth. Nanoparticles are then directed to living organisms,
organelles within the cells and individual protein or RNA molecules. This
property is related both to the harmful effects of nanoparticles on the living
kingdom and the pharmaceutical or biochemical studies conducted voluntarily,
to the level of peptide molecules.
5. Quantum confinement. Changes in size-dependent properties also include quan-
tum confinement, a phenomenon which causes spontaneous properties of
semiconductivity, conductivity or electric insulation for neighbouring particles
less than 10 nm in diameter [
14
].
In most cases, the dispersion medium of nanoparticles that come in close contact
with man or other components of the living kingdom is air or water. According to
their size, nanoparticles can be classified as ultradispersion systems (1-50 nm), high
dispersion systems (50-100 nm) or sedimentable particles (100-1,000 nm). Sedi-
mentable particles consist of either large particles or fractal-type particles [
14
].
Very fine colloidal suspensions present in water can be destabilised and turned to
sedimentable materials easily.
Nanoparticles have always circulated in the atmosphere of the planet. They
derive both from volcanic eruptions or fine desert dust lifted by air currents, and
interstellar dust as such or resulting from meteorite disintegration.
Nanoparticles are also the result of various human activities, from the primary
exploitation of quarry materials to exhaust gas, thermal power or cement plant
stacks, engine jets or fireworks.
Chemically speaking, nanoparticles are of infinite diversity, as their diversity
borrows both the nature of dust or fluids existing on the planet or generated
naturally and all materials produced by human activities. Therefore, nanoparticles
can be metal or non-metal particles in an elementary state, as well as inorganic and
organic substances resulting from their combination.
Fine aerosols consisting of metal particles are usually spherical. They can be
crystals, but in ionic state they form sub-colloidal or colloidal systems. These fields
include
combinations of about 50-60 metal
atoms
(for 1
d
10-nm
<
<
nanoparticles), but they can reach even 500-2,000 atoms.
The intuitive classification of metal particles is given in Fig.
1.2
[
13
].
In a finely divided state, many metals react instantaneously with the main
atmospheric components (oxygen, nitrogen, carbon dioxide), even with those
existing in very small concentrations, namely in a similar dispersion state. In this
way,
the chemical nature of nanoparticles of a certain type present
in the
