Civil Engineering Reference
In-Depth Information
[
]
kK
K
Pollutant
Pollutant
r
=
[
]
1
+
where
r
represents the reaction rate,
k
the rate constant,
K
the adsorp-
tion coeffi cient of the pollutant on the photocatalytic paint and [Pollut-
ant] the concentration of the pollutant of concern.
•
Presence of mixtures of pollutants:
Due to the competition on the
adsorption of the different pollutants on the surface of the photocata-
lyst, the photocatalytic reaction rate for a single component is normally
lower in the presence of different kinds of pollutants (Ao
et al.
, 2004;
Chen and Zhang, 2008).
The present chapter describes the different fi elds in which photocatalytic
paints are used, providing a critical overview of both their advantages and
drawbacks, and outlining the areas in which further research is still needed,
such as the evaluation of the potential loss in the catalytic effi ciency during
the lifecycle of photocatalytic paints.
15.2 Application of photocatalytic paints
in an outdoor environment
15.2.1 Investigation into the photocatalytic effi ciency of
active outdoor paints at the laboratory scale
Several experiments corroborated the initial observations carried out by
Fujishima and Honda (1972), and demonstrated that TiO
2
powder, and
more particularly anatase TiO
2
, was capable of degrading air pollutants
(e.g., N
2
O, NO, NO
2
, SO
2
, BTEX, carbonyl compounds, alcohols, CO, CH
4
,
CFCs, etc.) (Wang
et al.
, 2007; Mo
et al.
, 2009; Laufs
et al.
, 2010; De Richter
and Caillol, 2011) when exposed to solar-like radiation. Considering the
promising results obtained in laboratory-scale experiments, TiO
2
has since
been incorporated into building materials, such as concrete, glass or paint
(Allen
et al.
, 2009; Pacheco-Torgal and Jalali, 2011; PICADA n.d.).
The typical experimental set-up consists of a chamber test in which a
controlled atmosphere with a known concentration of pollutant is created
(Fig. 15.1). The paint, installed inside the chamber, is irradiated with a light
source of a well characterized emission spectra, while the pollutant is
fl ushed through the chamber and its concentration is monitored at both the
entrance (before the photocatalysis) and the exit (after the photocatalysis)
of the chamber.
In order to quantify the photocatalytic effi ciency of the paint accurately,
it is necessary to assess for infl uence of competitive depletion mechanisms
that could affect the concentration of the pollutant of concern inside the
chamber. Thus, the experiments involve the evaluation of:
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