Self-cleaning tiles and glasses for eco-efficient buildings - Nanotechnology in Eco-efficient Construction - page 333

ferring the microstructure of selected plant surfaces to practical materials
like tiles and façade paints, superhydrophobic surfaces were obtained
(Lotus effect). Superhydrophilic materials were developed by coating glass,
ceramic tiles or plastics with the semiconducting photocatalyst titanium
dioxide (TiO 2 ). If TiO 2 is illuminated by light, grease, dirt and organic con-
taminants are decomposed and can easily be swept away by water (rain).
TiO 2 -coated ceramic tiles are considered to be very effective against
organic and inorganic materials, as well as against bacteria. There is general
interest in the application of these tiles in hospitals and care facilities to
reduce the spread of infections and the threat to patients whose immune
system has been weakened, in public and commercial facilities and schools
to improve the hygienic conditions and in residential kitchens, baths and
fl oors to promote family hygiene and to reduce housework. Furthermore,
these tiles show superhydrophilic behaviour. Grease, dirt and other staining
materials can easily be swept away with a stream of water. Superhydrophi-
licity, combined with the strong photocatalytic oxidizing properties, makes
this tile self-cleaning in exterior applications.
With the increasing concern for human health and quality of life, the use
of TiO 2 for disinfection becomes more and more important. In the ceramic
and building industries, there is a special interest in the photoinduced bac-
tericidal effect of TiO 2 . 49 This is particularly true when the ceramic is going
to be placed in microbiologically sensitive environments, such as medical
facilities, and food industries where biological contamination must be
prevented. 50
Applying antibacterial TiO 2 building materials to indoor furnishings has
been shown to be an effective way to decrease bacterial counts to negligible
levels. It was reported that in an operating room in a hospital the number
of bacteria on the wall surface was reduced to zero and the bacteria in the
air was also decreased signifi cantly after installing photocatalytic tiles. The
longer term effect was much better than the spraying of disinfectants. 51
Several companies, such as TOTO, Karpery and Biocera, have commercial-
ized the concept of a deposited thin fi lm semiconductor photocatalyst on
ceramics as an antimicrobial agent. Their semiconductor photocatalyst thin
fi lm ceramic products exhibit both UV light-induced antimicrobial agent
and deodorizing properties. 54 The light-induced bactericidal activity of TiO 2
can also be used to control biological growth on concrete surfaces. A sche-
matic mechanism of photocatalytic anti-bacterial action is given in Fig. 14.3.
Unsightly stains due to the growth of biofi lm may cause the loss of aesthetic
beauty, particularly in places where design features or maintenance faults
result in frequent wetting of the building surface. 53 This could also trigger
chemical changes of concrete surfaces and decrease their durability. 55 Pho-
tosynthetic algae can only grow where sunlight is available, so that photo-
catalytic technology is an ideal control method.

￿ ￿ ￿ ￿ ￿ ￿