Self-cleaning tiles and glasses for eco-efficient buildings - Nanotechnology in Eco-efficient Construction - page 331

There are not many reported patents on materials that are stable, anti-
bacterial and can be activated by visible/room light. The CREST-DIT, Ireland
patented materials are the fi rst to claim anti-microbial visible light photo-
catalytic action and it is believed that they could represent the best available
technology to deal with the persistent problems of E. coli and MRSA.
There are some interesting reports that tackle the problem of the high
temperature stable anatase titania, and spraying the solution directly onto
the ceramic surfaces. One such report (JP 2001031483 (A)) set out to solve
the following problem: to form a strong photocatalytic layer taking advan-
tage of the remaining heat immediately after burning by directly spraying
a photocatalyst liquid on a ceramic substrate during cooling immediately
after burning. The reported solution is that the ceramic substrate is a ceramic
building material necessitating high-temperature burning such as tile, brick,
ceramic plate or roofi ng tile. Preferably, a mixture of anatase TiO 2 sol and
SiO 2 sol is used as the photocatalyst liquid for a ceramic substrate having
coarse porous surface, and a photocatalyst liquid containing peroxotitanic
acid is used for a ceramic substrate having a smooth surface. The surface
temperature suitable for the formation of the photocatalytic layer is prefer-
ably 350-500°C. The photocatalytic layer formed on a coarse porous surface
of a substrate is resistant to the peeling from the substrate because the TiO 2
particles are fi xed to the pore of the porous surface of the substrate to
semi-permanently exhibit an excellent effect. The photocatalyst liquid con-
taining peroxotitanic acid preferably forms fi ne particles of anatase TiO 2 by
heat treatment to form a photocatalytic fi lm having high activity. The
product has air-cleaning, stain-proofi ng and antibacterial characteristics.
Another report (KR 20020043133 (A)) provides a novel method of
making photocatalytic titanium oxide sol by improving the existing hydro-
lysis process of the sol-gel method. It is a method for making acidic titanium
oxide sol and basic titanium oxide sol, inducing the crystal growth of anatase
type at high temperature and pressure. The above titanium oxide sol for the
photocatalyst has excellent properties of dispersion and coating and pho-
tocatalytic ability to decompose various organic materials.
It can be seen that there are numerous reports/patents that deal with high
temperature stable anatase titania, but no such reports include activation
due to visible light and photocatalytic properties at high temperatures and
that are also used in the application area of anti-bacterial ceramic tiles.

￿ ￿ ￿ ￿ ￿ ￿

14.3 Mechanism of self-cleaning glasses and tiles
14.3.1 Self-cleaning properties

It is known that titanium dioxide surfaces display excellent anti-fogging and
self-cleaning abilities because of the superhydrophilic attributes of TiO 2