Biomedical Engineering Reference
In-Depth Information
by the reaction themselves. This is widely used in the chemical industry.
The catalytic effect takes place at the surface of the metal. Molecules bond to
the atoms of the metal and can dissociate, providing opportunities for other
molecules or molecule fragments to bond to these fragments and form new
molecules. Looking for the right catalysts in combination with the appropri-
ate reaction conditions is an ongoing topic in chemical research. Since these
processes take place at the surface, a larger surface area makes the process
more efficient. Smaller particles have a larger surface-to-volume ratio and
are therefore more effective catalysts. Especially since some catalysts, such as
platinum or rhodium, are very expensive metals, a high surface-to-volume
ratio can make a process economically viable for the chemical industry.
Making small metal particles and maintaining the dispersion of these par-
ticles under reaction conditions has been one of the more important research
goals for many decades and can be regarded as “nanotechnology avant la
let t re.”
Usually catalysis is used to create high-order chemical molecules. However,
the dissociation of the molecules at the surface of the metal can also be used to
make them react to smaller molecules, eventually ending up as biocompatible
molecules and water. This principle is used in some of the remediation con-
cepts for polluted sites. Of course, also in this case, a high surface-to-volume
ratio makes the process more efficient and therefore nanoparticles are also
employed. Depending on the kind of pollution, the soil, and geological cir-
cumstances, different strategies are used. Sometimes the catalytic nanoparti-
cles are injected into the soil and sometimes the water is extracted and allowed
to flow through a purification installation. If nanoparticles are entered into
the soil, not only should they not be more polluting themselves, the reaction
conditions cannot be controlled and will be very mild. In purification installa-
tions, these limitations are absent, but they can only be employed if the pollu-
tion can be extracted from the ground.
Another method of catalytic breakdown of more complex organic mole-
cules is the use of titanium dioxide nanoparticles or layers in combination
with light, preferably of small wavelengths (ultraviolet). This principle is also
used in small-scale water purification in aquaria. Coatings of titanium diox-
ide are used in self-cleaning surfaces of glass but are also employed on street
surfaces to break down organic by-products of traffic before they enter the
aqueous environment, effectively reducing the pressure on sewage cleaning
installations.
5.6 Discussion
From the above, it has become clear that nanotechnology will have many
applications in agriculture, food, and water. This is not surprising since it is a
