4. Conclusions
Nanocrystalline TiO2 (15–30 nm) was found to be highly dispersed
in aqueous medium at neutral pH upon modification by tiron,
ascorbic acid and rutin. Formed transparent, colored colloids
show low light scattering as the result of a negligible aggregation
of nanoparticles. In addition, synthesized surface charge transfer
complexes sensitize TiO2 to visible light, as confirmed by photocurrent
measurements. In the presence of oxygen significantly higher
photocurrents are generated than those recorded in its absence. As
a consequence of oxygen reduction superoxide is formed. This primary
reduction product opens a possibility to form other reactive
oxygen species, like hydrogen peroxide and hydroxyl radicals. Generated
reactive species are responsible for oxidation of organic
compounds, but may also be utilized in bacteria killing [25]. Similar
nanomaterials were also used to prepare photoactive coatings
on glass substrates. SEM images revealed a uniform and compact
structure of the films. Their thickness has been estimated by spectroscopic
ellipsometry to be ca. 25 nm. TiO2 films impregnated with the tested modifiers show a photocatalytic activity, proved by
oxidation of terephthalic acid upon visible light illumination.
Described visible-light active and highly dispersed nanocrystalline
materials based on titanium dioxide in aqueous media at neutral
pH may find a variety of medical applications, where a shortterm
photoactivity is expected (e.g., as bactericidal photoactive liquids
and coatings). Such applications may appear possible, since all
three modifiers are natural, non-toxic compounds.
Acknowledgments
Authors would like to thank Dr. Elzbieta Bielan _ ´ ska for SEM measurements,
Dr. Danuta Semik for TEM measurements and Ms. Agnieszka
Puciul-Malinowska for ellipsometry measurements. The
support from National Science Centre within the Grant No. 2011/
01/B/ST5/00920 is highly acknowledged. The research was carried
out with the equipment purchased thanks to the financial support
of the European Regional Development Fund in the framework of
the Polish Innovation Economy Operational Program (Contract
No. POIG.02.01.00-12-023/08). R.S. acknowledges the financial
support from the project Interdisciplinary PhD Studies ‘‘Molecular
sciences for medicine’’ (co-financed by the European Social Fund
within the Human Capital Operational Programme)