Civil Engineering Reference
In-Depth Information
14
Self-cleaning tiles and glasses for
eco-effi cient buildings
D. SYNNOTT, N. NOLAN, D. RYAN, J. COLREAVY and
S. C. PILLAI, FOCAS Institute, Republic of Ireland
DOI
: 10.1533/9780857098832.3.327
Abstract
: Self-cleaning and anti-bacterial activities of the photocatalyst
titanium dioxide make it a superior compound for use in the ceramics
and glass industry. Photocatalytic products have been on the market
since 2001. Photocatalysis is a photochemical process that semi-
conductor materials such as titanium dioxide undergo when irradiated
by light of a certain wavelength. A major drawback in commercializing
conventional TiO
2
photocatalysts for ceramic applications is the large
band gap of these materials which restricts its usefulness to outdoor
environments. Titanium dioxide can only be activated upon irradiation
with a photon of light <390 nm in the ultraviolet region. Ultraviolet light
makes up less than 5% of the solar spectrum, whereas the spectrum
consists of ∼40% visible light. Therefore, in order to utilize TiO
2
to its
full potential and use it in an indoor environment, it is necessary to
decrease the band gap size facilitating visible light absorption. In this
chapter recent developments in the preparation of visible light activated
catalysts are provided. A brief outline of various commercial
photocatalytic tiles and glass products are listed. A general scientifi c
mechanism of anti-bacterial action and self-cleaning activity of
photocatalysts are also explained in detail. Finally, projected market
growth, future trends and recommendations to improve the
photocatalytic properties for the applications of tile and glass are
described.
Key words
: self-cleaning tiles, glass, anti-bacterial activity, solar and
visible light.
14.1 Introduction
In 1972, Japanese researchers Fujishima and Honda demonstrated the
powerful semiconductor capabilities of titanium dioxide, TiO
2
, in the split-
ting of water in a photoelectrochemical cell. Their work ignited a revolution
in the world of semiconductor research with Frank and Bard going on to
demonstrate titanium dioxide's unique properties for environmental reme-
diation through the reduction of CN
-
in water
1-4
in 1977, and Ollis using
TiO
2
for the mineralization of organic pollutants in 1983.
5-7
In the 1990s,
following Graetzel's paper on the dye-sensitized solar cell,
8,9
TiO
2
became
one of the most internationally researched semiconductor materials. The
327
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