2. ENVIRONMENTAL ChEMISTRy & TEChNOLOGy 2.1. Lectures

Chem. Listy, 102, s265–s1311 (2008) Environmental Chemistry & Technology
P83 FuNGICIDAL EFFECT OF PRINTED
TITANIuM DIOxIDE LAyERS
MáRIA VESELá, MICHAL VESELý, PETR DZIK,
JAnA CHOMOUCKá and LEnKA ŠUPInOVá
Brno University of Technology, Faculty of Chemistry, Purkyňova
118, 612 00 Brno, Czech republic,
vesela@fch.vutbr.cz
Introduction
Microorganisms are crucial and inevitable part of life on
Earth. They are found basially everywhere – in air, soil, in
animal and human bodies, even in places with extreme conditions.
Microbial contamination is a serious issue which has
to be dealt with in numerous cases of everyday life. Various
sterilization and dissinfecting methods have therefore been
developed so far.
Photocatalytic processes on thin layers of titanium dioxide
represent a new approach to the everlasting struggle
against microbial contamination. Reactive oxygen species
generated on the surface of irradiated TiO 2 inactivate most
type of microbes 1 . Apparently, titanium dioxide coated surfaces
self-reducing the population of microbes to minimal level
and preventing their growth would be of a great importance.
Most photodegradation reactions on organic substrates
are based on the oxidative power of photoinduced electronic
holes or are mediated by HO • radicals. Such reaction usually
lead to a complete mineralization of organic substrate to carbon
dioxide and water. However, it is necessary to provide a
reducible reactant (i.e. electron acceptors) which would react
with photogenerated electrones. In most cases of photocatalytic
degradation reactions, oxygen is present and it acts
as primary electron acceptor. Oxygen is thus transformed to
superoxide radical (O 2 •– ) and in this way a hydroxyl radical
can be produced:
TiO (h ) + H O → TiO + HO + H
+ • +
2 vb 2 ads 2 ads
TiO (e ) + O + H → TiO + HO ↔ O + H
– + • • – +
2 cb 2ads 2 2 2
(1)
Experimental
M a t e r i a l a n d M e t h o d s
Sol and substrate preparation. Sol-gel technique
was applied to titanium dioxide thin films preparation using
titanium(IV) propoxide as titanium precursors. A mixture
of absolute ethanol and acetylacetone (ACAC) was added
to titanium(IV) propoxide (TTP) under continuous stirring.
Then a small amount of water in ethanol was dropped at
last to the previously mixed solution. Soda lime glass plates
with sizes of 50 × 50 × 1.5 mm were chosen as a substrate for
immobilization of TiO 2 thin films. Soda lime glasses were
treated in boiling 9M sulphuric acid. Before the preparation
of the thin films, each glass was pre-treated in order to eli-
(2)
(3)
s505
minate the dust, grease and other residues using liquid surfactants
and dried under air flow.
Sol application was performed in a novel innovative
way utilizing a modified office inkjet printer. Ink cartridges
were removed from the printer and the ink tubing and printhead
were flushed and purged with anhydrous propanol.
“Virgin empty” spongeless carts were supplied by MIS Associates,
USA. Sol was filtered through 0.2 μm mesh size
syringe filter and loaded into one “virgin empty” cart. This
cart was installed into the printer in the black position and after
a series of head cleaning cycles a perfect nozzle check pattern
was obtained. Cleaned glass plates were then mounted
into a modified CD holder, fed into the printer and printed
with “black only” driver setting. The colour of the printed
pattern was varied in different shades of grey (100 %, 95 %,
90 %, 80 %, 70 %, 60 %) and thus glasses with varying sol
loading were printed. The resolution, print speed and media
settings were also varied and their influence on the resulting
TiO 2 layer properties was evaluated. Two way of printer setting
were chosen for thin layer of TiO 2 preparation – slow (S)
and rapid (R). The sample marked as 100 R corresponds to
100 % of sol loadings printed by rapid way.
Layer treatment. After this procedure, the coated glass
plates were dried in the oven at 110 °C for 30 min. Finally,
the deposited layers were thermally treated in a calcination
furnace at 450 °C for 4 hours.
P h o t o c a t a l y t i c I n a c t i v a t i o n o f
Y e a s t s
A 24-hour culture of yeast Candida vini CCY 29-39-3
(provided by Slovak Yeast Collection, Bratislava) was prepared
at 25 °C. After the cultivation, 10 ml of culture medium
was sampled into a plastic test tube, rinsed twice and centrifuged
at 4,000 rpm for 6 minutes. The supernatant was discarted
and the yeast sediment was diluted with 1 ml of distilled
water an throroughly mixed.
A titanum dioxide coated glass plate was irradiated by
UV lamp for 30 minutes in order to obtain a superhydrophilic
surface. 25 μl of diluted yeast suspension was pipetted onto
the glass plate and evenly spread across its surface. Then the
glass plate with yeast suspension was placed in a sreaction
chamber. The chamber consisted of a Petri dish with reflective
aluminum foil bottom and quartz glass cover. A few
drops of water were aplse placed into the reaction chamber in
order to maintain the humidity.
The reaction chamber was irradiated by 4 fluorescent
lamps Sylvania Lynx-S 11 W with emission maximum at
350 nm. The irradiation intensity was 1 mW cm –2 within
290–390 nm spectral region. Irradiated samples were dyed
and observed by fluorescent microscopy.
S u r v i v a l R a t i o C a l c u l a t i o n
The exposed yeast suspension was mixed with 25 μl acridine
orange solution (1 × 10 –4 mol dm –3 ) in phosphate buffer
of pH = 6. After thorough mixing, the sample was observed
with epi-fluorescent microscope nikon Eclipse E200.