Civil Engineering Reference
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private housing, but mainly of medical-related environments, such as oper-
ating theatres, common rooms and patient rooms - due to the chance to
induce the death of bacteria, viruses, as well as allergens and fungi.
The mechanism is similar to that of photocatalytic degradation: active
species are once again surface hydroxyl radical species produced by photo-
generated holes, and superoxide ions produced by photogenerated elec-
trons, which damage or destroy cell walls of biological materials (Mills and
Lee, 2002; Gerrity et al. , 2008). A more detailed explanation is given by
Hamal et al. (2009), who ascribe the photosterilization effect to the oxida-
tion of complex proteins and to the inhibition of enzymatic functions of
bacterial cells, which lead to ultimate cell death. In this respect, the employ-
ment of Ag-doped titanium dioxide is gaining much attention so as to
achieve an easy decontamination and disinfection of common rooms and
offi ces, as well as of medical equipment and operating theatres (Page et al. ,
2007; Wysocka-Krol et al. , 2011).
Antibacterial activity was also described as a means to control biological
growth on concrete surfaces and avoid unsightly stains. As described by
Kurth et al. (2007), biofi lm growth on concrete and mortar causes the trig-
gering of undesirable chemical and aesthetical changes. The introduction of
TiO 2 in the material does not explicate a strictly bactericidal activity in this
frame, but more properly an anti-vegetative effect. Polo et al. (2011) inves-
tigated the possibility of using titanium dioxide as a control technology to
counteract biofi lm microorganism growth, and reported the photokilling
effect of immobilized TiO 2 nanopowders on planktonic cells; conversely, no
cell inactivation was observed on young biofi lms, suggesting that possible
applications of TiO 2 should focus on preventative measures rather than on
the disaggregation of already existing biofi lms. Linkous et al. (2000), and
Linkous and Robertson (2006) also reported the inhibition of algae adhe-
sion on cement substrates and on roofi ng membranes modifi ed with TiO 2
(and WO 3 ).
￿ ￿ ￿ ￿ ￿ ￿
13.4 TiO 2 in cement-based materials
Since their earliest appearance in Japan at the end of twentieth century, the
diffusion of building materials modifi ed with photocatalytic components
has been constantly diffusing, spreading also to European countries. This is
correlated with the increase in the generation of pollution and depletion of
natural resources caused by intense and rapid industrial expansion, which
pushes towards the development of sustainable materials, technologies and
energy sources.
The widespread commitment inside the scientifi c community in the fi eld
of sustainability has focused much on purifi cation devices, both for waste-
water treatment and to improve the quality of air in industrial areas and
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