Functional photocatalytic films for green buildings: From fundamental science to
engineering
Lars Österlund
Department of Engineering Sciences, The Ångström Laboratory, Uppsala University
P O Box 534, SE-75121 Uppsala, Sweden.
Email:
The possibility to increase human comfort and reduce the global footprint of buildings is a
powerful driving force for introduction of new building technology. Introduction of
functional coatings in buildings can meet some of these demands. We demonstrate here that
the TiO
2
based photocatalytic films can be tailored such that they can be used for indoor air
cleaning in windows with sustained and increased activity, or as coatings or additives in
cement materials. Three approaches to achieve these improved functions are presented. First,
enhanced photocatalytic activity is obtained by synthesis of controlled amount of <001>
preferential orientation of nanostructured anatase TiO
2
films by reactive dc magnetron
sputtering. The preferentially oriented films imply a textured surface that expose up to 40%
of {001} surfaces, and whose reactivity towards oxidation of acetaldehyde increases non-
linearly with fraction of <001> orientation. About 10-fold increased reactivity and enhanced
resilience towards deactivation is observed for the film exhibiting 40% <001> orientation. IN
a second approach, chemical surface functionalization of TiO
2
by means of photo-fixation of
SO
2
and NO
2
are done to bind sulphate and nitrate groups to the surface, and hence acidify
the surface. By doing so, the wetting properties of the TiO
2
films are modified, Furthermore,
bonding of weak acidic intermediates from VOC photo-degradation and subsequent surface
deactivation is thereby avoided. Atomic scale insight into the sulphate surface
functionalization and the bonding of strongly bonded intermediates, and formic acid in
particular, are obtained by interplay between in situ Fourier transform infrared spectroscopy,
in vacuo infrared absorption spectroscopy and density functional theory calculations. In the
third approach, TiO
2
is deposited on visible-infrared light absorbing film, whereby heat
generated in the underlying light absorbing film heats the TiO
2
film. We show that increasing
the temperature of the TiO
2
film results in an increased photocatalytic activity by two
mechanisms: thermal activation to increase reaction kinetics, and by shifting the water gas-
surface equilibrium coverage to free surface sites for reactant molecules. We generalize the
results, and discuss their implications for green building technology and possible scenarios
for their implementation.
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