Civil Engineering Reference
In-Depth Information
•
Additives:
A wide range of additives are added to the formulation of
the paint in order to favour the drying and curing process, remove the
bubbles formed during painting, increase the chemical and mechanical
resistance, etc.
Several parameters have been observed to affect the photocatalytic
effi ciency of paints for the oxidation of air pollutants under irradiation
of the photocatalytic paint (Mo
et al.
, 2009). The most critical parameters
are:
•
Wavelength of incident radiation:
The wavelength of the incident radia-
tion has to be appropriate in order to excite the electrons of the photo-
catalyst and initiate the photocatalytic process.
•
Light intensity:
The reaction rate increases with increasing light
intensity.
•
Effective surface area of the photocatalyst:
A higher surface area of the
photocatalyst increases the photocatalytic rate.
•
Paint constituents and interaction with the photocatalyst:
It has recently
been observed that paint constituents (e.g., binder) have a considerable
infl uence on the performance of the photocatalytic paint (Aguia
et al.
,
2010). In this sense, it has been observed that the nature and proportion
of the different paint constituents can have a signifi cant effect in terms
of enhancing or diminishing the photocatalytic effi ciency of the catalyst.
Further research is still needed in order to understand the mechanism
by which each of the single paint constituents affects the photocatalytic
effi ciency of photocatalytic paints, in order to better optimize their
formulation.
•
Relative humidity:
Water molecules adsorbed on the photocatalytic
paint seem to enhance the photocatalytic effi ciency of TiO
2
through the
formation of hydroxyl radicals which, in turn, oxidize the air pollutants.
However, an excessive relative humidity (
70%) inhibits the photocata-
lytic degradation of air pollutants, due to the competition for adsorption
sites on the photocatalyst surface (Pichat, 2010).
>
•
Temperature:
A rise in the temperature speeds up the kinetics of the
reaction between the pollutants and the photocatalyst, while at the same
time decreasing the adsorption of the pollutants on the surface of the
photocatalytic paint. Since the net photocatalytic reaction rate is a com-
bination of both processes, a maximum photocatalytic oxidation rate is
obtained at the optimum temperature (Obee and Hay, 1997).
•
Concentration of the pollutant:
The relationship between the concentra-
tion of the pollutant and the photocatalytic rate is generally governed
by the Langmuir-Hinselwood model (Shiraisi
et al.
, 2007), according to
which the reaction rate increases with the concentration as described in
the equation:
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