Civil Engineering Reference
In-Depth Information
tungsten light bulb, the effi ciencies obtained for the degradation of volatile
organic compounds were very low. Thus, degradation of formaldehyde and
terpene compounds (pinene, limonene) was possible only at high concen-
tration levels, while CO was not observed to be signifi cantly degraded under
any of the evaluated conditions.
Antimicrobial and antifungal effect
Hochmannova and Vytrasova (2010) demonstrated the inhibition of the
potential cell growth on plates coated with photocatalytic paints prepared
using ZnO and TiO
2
Degussa as photocatalysts. ZnO-based photocatalytic
paints were able to completely inhibit cell growth for
Escherichia coli
,
Pseudomonas aureaginosa
,
Staphylococcus aureus
,
Aspergillus niger
e
Peni-
cillium chrysogenum
, and were therefore suggested as optimum photocata-
lysts for the preparation of antimicrobial photocatalytic paints, where a
highly sterile environment (e.g., in hospitals) is required.
This antimicrobial effect may be due to the attack of the microorganisms
by the hydroxyl radicals and superoxide anions created during the irradia-
tion of the photocatalyst surface (Section 15.1).
15.4 Potential formation of by-products
By-products formed during the photocatalysis can be either intermediate
products or secondary emissions. Some of these by-products might even be
more harmful compared to the original pollutant degraded by the photo-
catalytic paint, and their formation should therefore be avoided wherever
possible.
•
Intermediate products
are formed due to the incomplete photocatalysis
of a certain pollutant.
•
Secondary emissions
are formed due to the photo-oxidation of the sup-
porting material in which the photocatalyst is embedded. Previous
studies indicate that various compounds are released due to the oxida-
tion of the organic constituents of the material supporting the photo-
catalyst during the photocatalytic process.
15.4.1 Formation of intermediate products
Recent studies have shown that the reactions achieved by the degradation
of pollutants on photocatalytic paints are generally not complete, and the
reaction stops along the way, giving rise to the formation of intermediate
products. It is known that NO
2
is formed as an intermediate product by the
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