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nanoparticles onto the respective substrate layers during the progressive development of
the reactive filter system. It was then possible to obtain a filter-sandwich structure with
chemical catalyst complexes and catalytically active enzymes on top of this ‘anchor
layer’. The filter-sandwich structure can be adjusted in line with various filter substances
and security requirements in air and drinking water purification procedures. Tests on the
catalyst system with accordingly coated polyethylene filter beads have shown that
pesticides in drinking water can be reduced by 99% in less than 2 minutes at a
continuous flow rate. The filter performance during the tests was sustained for a period
of 60 days (see Figure 3.1).
Figure 3.1 Self-cleaning filter system using chemical and enzyme catalysis (source: Naval
Research Laboratory)
Also in the US, the Argonne National Laboratory has developed a security system using a
super-absorbent gel which enables radioactive residue to be neutralized and removed
from porous surfaces of buildings or monuments in the event of, for example, a nuclear
attack using a ‘dirty bomb’. If such an event were to occur, civil security forces would
apply the super-absorbent polymer gel to the contaminated surfaces in the form of an
aqueous suspension using a spraying device. The foam acts by penetrating the porous
surface and trapping the radioactive particles within the polymer structure, where they
bind to tailored nanoparticles that are contained in the gel. The contaminated gel can
then be removed and recycled using a vacuum device so that only a small percentage of
the decontamination material has to be disposed of as radioactive waste. Efficacy trials
with various radioactive elements on building facades of cement and brick have shown
that the use of super-absorbent polymer gel can remove over 98% of radioactive
elements from cement components and over 80% of radioactive elements from the entire
building surface.
An example of the relevance of nanotechnology applications for civil security is a titanium
dioxide-based semiconductor photocatalyst developed by Erlangen-Nürnberg University.
It is able to use a larger proportion of sunlight in order to achieve a higher level of selfcleaning
in coatings than previous photocatalysts. Normally, titanium dioxide particles
can only use UV light, which only makes up around 2 – 3% of sunlight and accounts for
even less of artificial light in internal spaces. In order to sensitize titanium dioxide to the
far greater visible light spectrum, Professor Kisch’s team doped the photocatalytic
material with elements such as carbon. They achieved an optimum catalytic effect with 2
– 3% carbon doping of the titanium dioxide crystal lattice. Moreover, the method
developed by the researchers for the production of the carbon-doped titanium oxide is
simpler, more easily reproduced, and has scope for wider use than the traditional
titanium dioxide production technique, which involves the oxidation of titanium sheet
metal in a natural gas flame. The different property profile achieved by the doping
method in comparison with traditional titanium dioxide photocatalysts should enable the
production of new photocatalysts with a higher degradation potential for chemical toxins
in the medium term. Materials coated with the doped photocatalysts were able to
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