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Titania and Silver-Titania Composite Films on Glass—Potent Antimicrobial Coatings


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Titania (anatase) and Ag-doped titania (anatase) coatings were prepared on glass microscope slides by a sol–gel dip-coating method. The resultant coatings were characterised by X-ray diffraction, X-ray absorption near edge structure (XANES), Raman, scanning electron microscopy (SEM), wavelength dispersive X-ray (WDX) analysis, X-ray photoelectron spectroscopy (XPS) and UV-vis techniques and shown to consist of anatase with ca. 0.2–1 atom% Ag2O. Photocatalytic activity of the coatings was determined by photomineralisation of stearic acid, monitored by FT-IR spectroscopy. Photocatalytically-active coatings were screened for their antibacterial efficacy against Staphylococcus aureus (NCTC 6571), Escherichia coli (NCTC 10418) and Bacillus cereus (CH70-2). Ag-doped titania coatings were found to be significantly more photocatalytically and antimicrobially active than a titania coating. No antimicrobial activity was observed in the dark—indicating that silver ion diffusion was not the mechanism for antimicrobial action. The mode of action was explained in terms of a charge separation model. The coatings also demonstrated significantly higher activity against the Gram-positive organisms than against the Gram-negative. The Ag2O–TiO2 coating is a potentially useful coating for hard surfaces in a hospital environment due to its robustness, stability to cleaning and reuse, and its excellent antimicrobial response.
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Titania and silver–titania composite films on glass—potent antimicrobial
Kristopher Page,
Robert G. Palgrave,
Ivan P. Parkin,*
Michael Wilson,
Shelley L. P. Savin
Alan V. Chadwick
Received 15th August 2006, Accepted 19th October 2006
First published as an Advance Article on the web 3rd November 2006
DOI: 10.1039/b611740f
Titania (anatase) and Ag-doped titania (anatase) coatings were prepared on glass microscope
slides by a sol–gel dip-coating method. The resultant coatings were characterised by X-ray
diffraction, X-ray absorption near edge structure (XANES), Raman, scanning electron
microscopy (SEM), wavelength dispersive X-ray (WDX) analysis, X-ray photoelectron
spectroscopy (XPS) and UV-vis techniques and shown to consist of anatase with ca. 0.2–1 atom%
O. Photocatalytic activity of the coatings was determined by photomineralisation of stearic
acid, monitored by FT-IR spectroscopy. Photocatalytically-active coatings were screened for their
antibacterial efficacy against Staphylococcus aureus (NCTC 6571), Escherichia coli (NCTC 10418)
and Bacillus cereus (CH70-2). Ag-doped titania coatings were found to be significantly more
photocatalytically and antimicrobially active than a titania coating. No antimicrobial activity was
observed in the dark—indicating that silver ion diffusion was not the mechanism for antimicrobial
action. The mode of action was explained in terms of a charge separation model. The coatings
also demonstrated significantly higher activity against the Gram-positive organisms than against
the Gram-negative. The Ag
coating is a potentially useful coating for hard surfaces in a
hospital environment due to its robustness, stability to cleaning and reuse, and its excellent
antimicrobial response.
1. Introduction
Staphylococcus aureus is a Gram-positive bacterium which
colonises approximately 30% of individuals in developed
countries, mainly in the nose or on the skin.
In a
colonisation of this type most people experience no symptoms
or any infection, however it is able to cause a variety of
diseases ranging from the trivial (e.g. boils) to the life-
threatening (e.g. toxic shock syndrome). Most S. aureus
infections can be treated with antibiotics
as these are due to
infection by methicillin-sensitive S. aureus (MSSA). However,
some strains of the organism (known as methicillin-resistant S.
aureus—MRSA) are resistant to a number of antibiotics, and
infections due to such strains are very difficult to treat.
MRSA infections are more common in hospital environments
where the organism is usually passed on by direct contact,
usually by the hands of health care workers (nosocomial
S. aureus has achieved methicillin resistance by
evolving both an efflux mechanism, which actively and non-
specifically expels antibiotics from the cell,
and by the
production of an altered penicillin binding protein PBP2a
the product of the mecA gene which is insensitive to
The spread of MRSA and other infections can
be controlled effectively through a rigorous hygiene regime.
Simple hand-washing is sufficient to help control the spread of
the organism,
however this is of little use if the hospital
environment is heavily contaminated.
Contamination of
surfaces touched by health care staff in the hospital environ-
ment is obviously a potential reservoir for nosocomial
infection by MRSA
and the organism can survive for
up to 9 weeks when it dries onto surfaces.
An antimicrobial
coating that actively disinfects hard surfaces touched by
nursing staff will help to break the nosocomial infection loop.
Such a coating would be particularly useful as a means of
disinfection in high traffic communal areas and on items such
as door handles, taps and toilet flushes. An effective
antimicrobial coating would not necessarily be limited to these
areas, but could be employed in various roles across the
hospital in both surgical and communal areas.
Titanium dioxide (TiO
) is receiving considerable research
interest as a photocatalyst and consequently an antimicrobial
coating. TiO
first came to the attention of the scientific
community when Fujishima and Honda demonstrated the
photolysis of water by a TiO
–Pt electrochemical photocell in
However it was not until 1985 that the efficacy of TiO
semiconductor particles as a means of microbial disinfection
was first realised by Matsunaga et al.
It was found that
platinised TiO
, when irradiated with ultra band gap UV
radiation, acted as an antimicrobial agent, as a result of
photocatalytic processes taking place on the TiO
surface. Mills
and LeHunte have written a key review in this area covering
photocatalytic and antimicrobial properties of titanium dioxide
and metal-doped titanium dioxide thin films.
Department of Chemistry, University College London, 20 Gordon
Street, London, UK WC1H 0AJ. E-mail:
Division of Microbial Diseases, UCL Eastman Dental Institute,
University College London, 256 Gray’s Inn Road, London, UK
School of Physical Sciences, Ingram Building, University of Kent,
Canterbury, Kent, UK CT2 7NH
PAPER | Journal of Materials Chemistry
This journal is ßThe Royal Society of Chemistry 2007
J. Mater. Chem.
, 2007, 17, 95–104 |95
Anatase titanium dioxide has a band gap energy (E
3.2 eV.
Irradiation of anatase TiO
with UV radiation
greater than E
causes promotion of an electron from the
valence band to the conduction band. This results in the
formation of an electron–hole pair. This is a free electron in
the conduction band, and a hole in the valence band.
These reactive species then participate in oxidation and
reduction processes either within the TiO
itself (electron and
hole recombination), or with adsorbates at the surface.
Disinfection of a surface by photocatalysed reactions on
is a popular possible alternative to using chemical
disinfectants such as chlorine bleach.
The effectiveness of the TiO
as a photocatalyst is in part
dependent upon the rate of production of hydroxyl radicals at
the surface of the semiconductor. This is in turn dependent
upon other factors. These include the energy of the light
illuminating the surface and the competition between electron–
hole recombination and the redox processes occurring on the
Titanium dioxide thin films have been formed on glass, steel
and other surfaces by a wide range of techniques, especially by
sol–gel and chemical vapour deposition.
Furthermore they
have been looked at as antimicrobial coatings and shown to be
efficient especially under sunlight or black light irradiation.
Commercial products making use of TiO
include self cleaning glasses such as Pilkington Activ2and
Saint Gobain Bioclean, self cleaning tiles (TOTO Inc.) and in
air purifiers.
The formation of silver-doped titania thin films
has received less attention.
Silver is incorporated into the
titania film by first forming the film, often using a paste
method using Degussa P-25, followed by impregnation with an
aqueous solution that contains silver ions.
Reduction of
this film by photolysis forms nanoparticulate silver nuggets
within a host titania matrix. These films have shown to be both
more and less active than the parent titania host matrix in the
photomineralisation of organic molecules.
The destruction
of a particular pollutant has been related to the sensitivity of
its radical and the ability of the silver–titania film to stabilise
photo-produced electrons and holes. The ability of silver–
titania thin films to act as antimicrobial coatings has received
scant attention, although one report on preliminary antimi-
crobial tests showed that the coating halts E. coli colony
The use of silver as a microbicide is well known
and a host of commercial products exist for use in wound
dressings, ear-pieces, face masks, catheters, plasters and even
for deodorisation of socks.
A number of commercial
antimicrobial surface treatments also exist which rely on the
microbicidal activity of the Ag
ion—these include AgION2
(AgION Technologies Inc.)
and SilvaGard2(AcryMed
In all of these instances the silver is impregnated in
the products in its nanoparticulate form or as a silver salt such
as silver nitrate. The mode of action has been shown to
correlate directly with the diffusion of Ag
into solution. This
mode of action works equally well in the dark as in the light as
it is not directly related to the photocatalytic mechanism
associated with the host titania.
In this paper we report the synthesis of titania and silver-
doped titania nanoparticulate thin films from a sol–gel route.
We demonstrate that the silver-doped titania thin films are
significantly more active than titania films both as a
photocatalyst and as an antimicrobial agent when illuminated
with 365 nm light. We show that the silver is present in the
films as Ag
O by XPS and X-ray absorption spectroscopy
(XAS). The silver-doped titania films are rugged and have
survived multiple reuses and cleaning with no depletion in
antimicrobial effect. We provide a comparison of the
antimicrobial efficiencies of the films for Gram-positive,
Gram-negative and spore-forming bacteria. Furthermore we
observe no antimicrobial activity from these films in the dark,
indicating that the mode of action is not, unlike previous
studies, due to silver ion diffusion. We conclude that the mode
of action of these films is related to the ease of stabilisation of
the photo-generated electron–hole pair. These new films are
easy to apply at the point of manufacture and have the
potential to be used in a clinical environment for reducing
bacterial loads and hence nosocomial infections.
The chemicals used in this investigation were all purchased
from Sigma-Aldrich Chemical Co; propan-2-ol; butan-1-ol;
pentane-2,4-dione (acetylacetone); silver nitrate; titanium (IV)
n-butoxide and acetonitrile. The thin films were prepared on
standard low iron microscope slides (BDH). These were
supplied cleaned and polished, but were nonetheless washed
with distilled water, dried and rinsed with propan-2-ol and left
to air dry before use (2 h).
Sol–gel synthesis
Ag-doped TiO
film. The procedure was carried out in air.
Titanium n-butoxide (17.02 g, 0.05 mol) was chelated with a
mixture of pentane-2,4-dione (2.503 g, 0.025 mol) in butan-1-ol
(32 cm
, 0.35 mol). A clear, straw yellow solution was
produced, with no precipitation. This was covered with a
watch glass and stirred for an hour. Distilled water (3.6 g,
0.2 mol) was dissolved in propan-2-ol (9.04 g, 0.15 mol)
and added to hydrolyse the titanium precursor. The solution
remained a clear straw yellow colour, with no precipitate.
The solution was stirred for a further hour. Silver nitrate
(0.8510 g, 0.005 mol) was dissolved in acetonitrile (1.645 g,
0.04 mol). This was added to the pale yellow titanium
solution, which was stirred for a final hour. After the final
stirring, the resultant sol was a slightly deeper yellow in
colour, but remained clear and without precipitate. The sol
was used within 30 min for dip-coating. The TiO
controls were made in a similar manner and to the same
Dip-coating. For dip-coating the glass microscope slides, the
sols were transferred to a tall and narrow 50 cm
beaker. This
ensured that most of the slide could be immersed in the sol. A
dip-coating apparatus was used to withdraw the slide from the
sol at a steady rate of 120 cm min
. If more than one coat was
required, the previous coat was allowed to dry before repeating
the process. Alternative substrate materials were also coated.
These included martensitic stainless steel; aluminium; brass;
galvanised steel and Pilkington float glass.
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Calcination/annealing. All films were annealed in a furnace
at 500 uC for one hour, with a rate of heating of 5 uC min
Characterisation of the synthesised coatings was carried out by
field emission scanning electron microscopy (SEM) (Jeol JSM-
6301F), wavelength dispersive X-ray (WDX) analysis (Philips
ESEM) and by Raman techniques (Renishaw 1000). Powder
X-ray diffraction (XRD) was carried out at glancing angles
with a 0.5 mm collimator using an AXS D8 Discover
instrument equipped with a general area detection diffraction
system (GADDS). The TiO
coating was examined with an
angle of incidence of 5uover an angular range of 10–66ufor a
15 min period. The Ag–TiO
coatings were examined with an
angle of incidence of 1.5uover an angular range of 10–62.5ufor
a 30 min period. X-Ray absorption near edge structure
(XANES) measurements were made on station 9.3 at the
CCLRC Daresbury Synchrotron Radiation Source. The
synchrotron has an electron energy of 2 GeV and the average
current during the measurements was 150 mA. Ag K-edge
extended X-ray absorption fine structure (EXAFS) spectra for
the films were collected at room temperature in fluorescence
mode using ten films added together to give effectively 20 layers
of the sample. Ag
O, AgO, and Ag metal powder were used as
standards, along with a Ag metal foil reference, these were
collected in standard transmission mode. The standards were
prepared by thoroughly mixing the ground material with
powdered polyvinylpyrrolidine diluent and pressing into
pellets in a 13 mm IR press. Spectra were typically collected
to k=16A
(kis the wave vector associated with the
photoelectron) and several scans were taken to improve the
signal-to-noise ratio. For these measurements the amount of
sample in the pellet was adjusted to give an absorption of
about md= 1 (where mis the absorption coefficient and dis the
sample thickness). The data were processed in the conventional
manner using the Daresbury suite of EXAFS programmes:
UV-vis spectra were obtained
using a Thermo Spectronic Helios Alpha single beam
instrument. WDX (Philips ESEM) was performed on car-
bon-coated samples, and SEM imaging (JEOL JSM-6301F)
was performed on gold-coated samples. X-Ray photoelectron
spectroscopy (XPS) measurements were carried out on a VG
ESALAB 220i XL instrument using focussed (300 mm spot)
monochromatic Al-K
X-ray radiation at a pass energy of
20 eV. Scans were acquired with steps of 50 meV. A flood gun
was used to control charging and the binding energies were
referenced to surface elemental carbon at 284.6 eV. Depth
profile analysis was undertaken using argon sputtering.
Photocatalytic activity
The photocatalytic activity of the films was monitored by
Fourier transform infrared (FTIR) spectroscopy (Perkin
Elmer Paragon 1000). The films were firstly activated by
30 min exposure to UV radiation from a 254 nm germicidal
lamp (Vilber Lourmat VL-208G; 8W—BDH/VWR Ltd). The
IR spectrum of each stearic acid over-layer was then recorded
over the range 3000–2700 cm
and the areas of the peaks
between 2950–2875 and 2863–2830 cm
(the C–H stretching
regions of stearic acid) were integrated. Monitoring the
integrated area is directly analogous to measuring the
concentration of stearic acid on the surface, and so can be
used to monitor the degree of photomineralisation after UV
irradiation. Slides were irradiated for a set period and then the
IR measured after each irradiation. The stearic acid over-layer
was applied by dip-coating the sample slides in a 0.02 mol dm
solution of stearic acid in methanol. To compare the
photocatalytic ability between samples it was ensured that
the initial peak areas were as close in value as possible. At the
end of the experiments the peak areas were normalised to the
initial starting value, such that comparison could be made.
Rates of photocatalysis (in molecules cm
) were also
calculated when the stearic acid decay profile could be fitted to
an appropriate rate law.
Water droplet contact angle
Photoactive films often demonstrate photoinduced super-
hydrophilicity (PSH). The degree of PSH can be gauged by
observing the change in contact angle of a water droplet on the
film surface after UV illumination. The samples were pre-
irradiated for 30 min under a 254 nm germicidal lamp (Vilber
Lourmat VL-208G—BDH/VWR Ltd), and then a 4 ml droplet
of distilled water was placed on the surface. The diameter of
the drop was then measured after it had settled. The volume–
diameter data were then entered into a computer programme
to calculate the contact angle of the water droplet. If a coating
demonstrates PSH after UV illumination, the water droplet
will be seen to spread out and have a very low contact angle
with the coating surface. Droplets were added and measured
after every consecutive 30 min of illumination time for 2 h.
Antibacterial activity
The antibacterial activity of the films was assessed against
Staphylococcus aureus (NCTC 6571), Escherichia coli (NCTC
10418) and Bacillus cereus (CH70-2; mixed vegetative and
endospore). Samples were tested in duplicate against a suite of
controls (detailed below). Sample coatings and the controls
were irradiated under a 254 nm germicidal UV lamp (Vilber
Lourmat VL-208G from VWR Ltd; 8 W) for 30 min to both
activate and disinfect the films. The sample slides were then
transferred to individual moisture chambers (made from Petri
dishes with moist filter paper in the base). An overnight culture
in nutrient broth (Oxoid Ltd, Basingstoke UK) was then
vortexed and 25 ml aliquots of the culture pipetted onto each
film in duplicate. The samples were then irradiated by a black-
light UV lamp, 365 nm (Vilber Lourmat VL-208BLB; 8W
from VWR Ltd) for the desired length of time. The irradiance
of the 365 nm lamp was measured at 1.4 mW cm
using a
Solarmeter Model 5.0 Total UV (A + B) hand held meter
(Solartech Inc., Michigan USA). After the desired irradiation
period, the bacterial droplets were swabbed from the surface
using sterile calcium alginate swabs (Technical Service
Consultants Ltd). The swabs were transferred aseptically to
4 ml ‘Calgon’ Ringer solution (Oxoid Ltd, Basingstoke UK) in
a glass bijoux containing 5–7 small glass beads. The bijoux was
then vortexed until the entire swab had dissolved. For all
bijoux, serial 10-fold dilutions of the bacterial suspension were
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prepared down to 1 610
in phosphate buffered saline
(Oxoid Ltd, Basingstoke UK) in a sterile 96 well plate. Each
dilution was then plated in duplicate onto agar. Mannitol salt
agar (Oxoid Ltd, Basingstoke UK) was used for S. aureus,
MacConkey agar (Oxoid Ltd, Basingstoke UK) was used for
E. coli and nutrient agar (Oxoid Ltd, Basingstoke UK) was
used for B. cereus. Inoculated plates were then incubated
overnight at 37 uC. After incubation a colony count was
performed for the dilution with the optimal countable number
of colonies (30 to 300 colonies). The data were then processed,
taking into account the dilution factor and the mean values of
duplicate experiments. The end result is a direct comparison of
the number of viable bacteria per ml on the samples to that on
a glass control. Experiments were repeated at least twice,
giving four data points for each sample tested. Experiments of
2, 4 and 6 h irradiation were conducted for S. aureus;
experiments of 6 h were carried out for E. coli and experiments
of 2 and 4 h were carried out for B. cereus.
Appropriate use of controls is essential in determining
whether the coating by itself, UV exposure by itself, or a
combination of the two is the cause of any observed
microbicidal effect. For each coating under test the following
system of positive and negative controls is required: (1) L+S+
(in UV light with an active substrate); (2) L+S2(in UV light
with an inactive substrate); (3) L2S+ (in the dark with an
active substrate); (4) L2S2(in the dark with an inactive
substrate). By using a system of controls as shown it is possible
to deduce from the results which conditions result in the
antibacterial effect. Photocatalytic coatings should not be
antimicrobially active without the activation by UV light, and
so only the L+S+ sample should show antibacterial activity. A
comparison of L+S+ and L2S2enables kill levels to be
calculated. (Note: depending upon the bacterium being
investigated, exposure to UV light by itself may have a
microbicidal effect. That is to say that the L+S2sample may
in some cases demonstrate a measurable kill.)
A simple sol–gel method was used to produce both the TiO
silver-doped TiO
films. The general principle behind this method
is the hydrolysis of a titanium precursor and its subsequent
polymerisation into a Ti–O–Ti network. By dip-coating the
microscope slides, a thin film of titanium precursor is deposited
and the gelation of the sol is substantially accelerated.
Annealing of the samples in a furnace drives off the last traces
of solvent, removes carbon and further enhances the polymerisa-
tion of the precursor into a crystalline anatase network.
The synthetic technique for doping Ag nanoparticles into a
titania film was similar to that of the pure titania film. Key to a
successful synthesis is the chelation of the metal sites involved;
this prevents agglomeration of nanoparticulate Ag and also
stops the instant gelation that occurs upon addition of AgNO
to an acidified titanium precursor. This effect was observed in
preliminary experiments without the use of stabilising solvents.
Acetylacetone (pentane-2,4-dione) in butan-1-ol was used to
stabilise the Ti centre and acetonitrile was used as a
coordinating solvent to stabilise the Ag.
Physical characterisation
The TiO
and Ag-doped TiO
films had a multicoloured hue,
dependent upon the angle from which they are viewed. The
appearance of the coatings is due to refringence effects
resulting from a small variation in the coating thickness.
Films of different thickness were made by varying the number
of dip-coats applied—however all films had a uniform
appearance, and were smooth. All of the Ag–TiO
had a
bluish–purple hue (possibly due to nanoparticulate silver),
with a distinct yellow–orange tinge in certain lighting
conditions. Notably TiO
films without silver did not show
the distinct bluish–purple hue or the yellow–orange tinge.
Under an optical microscope the surface of the one-coat film
–Ag was featureless, however in the four dip-coat film,
cracking of the surface was visible. All thicknesses of the
coating were resistant to standard scratch tests with a stainless
steel spatula, could not be removed by Scotch1tape and were
generally rugged. Indeed the film could only be removed by
chipping the glass substrate. Repeated dipping of the coatings
into distilled water had no effect on the coating’s surface,
which could not be wiped off. Depositing coatings onto
alternative substrates (brass, aluminium, SnO
, silica and
stainless steel) produced films of identical appearance to those
made on glass microscope slides. In particular, films deposited
onto stainless steel had excellent uniformity and retained the
ruggedness and adherence of the films coated on glass. This
robust physical behaviour is significantly better than paste,
traditional sol–gel and physical vapour deposition (PVD)
prepared titania films and is most akin to those made by
chemical vapour deposition (CVD)
such as the commercial
products Pilkington Activ and Saint Gobain Bioclean (ca.
25–50 nm thick anatase TiO
, deposited by ‘on-line’ CVD at
650 uC).
Powder X-ray diffractograms of the TiO
films were indexed
as anatase (I4
/amdz,a= 3.776 A
˚,c= 9.486 A
˚). The Ag–TiO
diffractograms were slightly less well defined than the TiO
diffractogram but did show peaks attributed to anatase TiO
(Fig. 1). Furthermore, the Ag–TiO
patterns exhibited one
other significant peak at 31.5u2hwhich was absent in the TiO
pattern and must therefore be due to the difference in
composition—possibly due to the incorporation of a Ag
compound rather than crystalline Ag. Database patterns for
crystalline Ag do not correlate with this observed peak. The
best pattern match for this peak and the remainder of the
diffractogram is for the silver oxides AgO and Ag
O. Both
silver oxide species correspond well with their most intense
peaks aligning with the additional peak observed in the
experimental pattern.
Raman analysis of both TiO
and Ag–TiO
types was
attempted in the range 100 to 1000 cm
. A characteristic
anatase TiO
scattering pattern was produced (Fig. 2), with a
sharp and intense peak at 143 cm
, and further peaks at 197,
396, 519 and 639 cm
in the undoped TiO
pattern. The less
well defined Raman pattern for the Ag-doped samples is most
probably due to the lower level of crystallinity in the samples—
as observed by the comparatively weak anatase peaks in the
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XRD. No Raman patterns for silver oxides were apparent.
This is most likely due to the low concentration of Ag
O in the
films and the poor Raman scattering power of Ag
O compared
with the TiO
Ag K-edge XAS spectra were collected for the three Ag-
doped TiO
films made from sols with Ag concentrations of
5%, 10% and 20%, Ag metal foil, Ag metal powder, Ag
O and
AgO powders. The Ag K-edge XANES data for the doped
samples are shown in Fig. 3(a) along with the corresponding
data for Ag metal powder, Ag
O and AgO. The energy scales
of all the spectra have been consistently normalised to the Ag
K-edge at 25 518 eV and the spectra shifted on the y-axis for
ease of viewing. Fig. 3(a) shows that the local environment of
the Ag atoms has a distinct effect on the shape of the XANES
spectra. This can be used to identify the local environment of
the Ag atoms in the Ag-doped TiO
films. In each case, the
shape of the XANES spectra for the doped films matches that
of the Ag
O standard, indicating that the silver is present in the
Fig. 1 Powder XRD patterns for four coat TiO
(lower trace) and two and four coat Ag–TiO
coatings (upper and middle traces respectively).
The Ag-oxide peak is marked with an asterisk (*).
Fig. 2 Raman pattern for four coat TiO
Fig. 3 (a) The Ag K-edge XANES for Ag
O, AgO, Ag powder and
Ag-doped TiO
films. No pre edge features were observed; (b) the Ag
K-edge XANES for Ag
O and Ag-doped TiO
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, 2007, 17, 95–104 |99
films as Ag
O [Fig. 3(b)]. The pattern for silver metal—as also
shown in Fig. 3(a) is very different to that observed and can’t
be detected in the samples measured. No bands were observed
before the edge in any of the XANES experiments.
Furthermore as the XAS gave such a good match to Ag
[see Fig. 3(b)] it is unlikely that the silver is present within the
titania lattice as a discrete solid solution Ag
this would give a different edge shape pattern. Hence the films
are best described as composites of anatase titania with small
amounts of homogeneously distributed silver (I) oxide.
SEM and WDX techniques were used to study the
composition and morphology of the coated surfaces. WDX
analysis confirmed the presence of Ag in the Ag–TiO
ratios of 1 part Ag to 100 parts Ti (or less). This was
significantly lower than the silver : titania ratio in the starting
sol (1 : 10). SEM imaging showed minor shrink cracking in the
single or double dip-coated films. The severity of shrink
cracking increased with increasing film thickness. At higher
magnifications, both coating types had similar morphologies,
consisting of granular structures. A high magnification
(6160 000) image of the two coat Ag-doped coating (Fig. 4)
displayed the granular and uneven nature of the coating. In the
top left quarter of the image, a high electron density artefact
can be observed. This indicates the presence of an agglomer-
ated island that contains Ag since this has a higher electron
density than the TiO
matrix—such islands were seen
randomly dispersed across the surface of the film. Also, during
the course of the SEM studies, the nanocrystalline nature of
the TiO
coating was observed—particles of 30 nm size on
average can be seen in a 6400 000 image (Fig. 5).
Observation of particles of this size correlates well with the
crystallite sizes calculated by the Scherrer equation from the
XRD line broadening—which corresponds best to nanocrys-
talline titania, rather than a fully crystalline phase. End on
SEM studies were also carried out to measure the thickness of
the films. The two coat materials had a thickness of
approximately 150 nm and a four coat material was
approximately twice this thickness, at ca. 300 nm.
X-Ray photoelectron spectroscopy was undertaken on two
sets of four coat Ag–TiO
films, one on a set exposed to UV
light and one on the films as made. Both gave the same XPS
profile. The titanium to oxygen atomic ratio was as expected
2 : 1, no other elements were detected other than carbon and
silicon at a few atom%. The percentage of the carbon
decreased dramatically on etching indicating that it was
residual carbon from within the XPS chamber. The Si
abundance was constant with etching and probably a result
of breakthrough to the underlying glass on regions where there
was a small crack in the titania coating, notably it was only
seen in one of the four samples analysed. Silver was detected
both at the surface and throughout the film and its abundance
was invariant with sputter depth. The silver was typically
detected at below 1 atom%—significantly lower than that in
the initial sol but comparable to that observed by WDX
analysis (values ranged around 0.2 atom%, however accurate
quantification was difficult at such low levels). The detection
limit of the instrument is approximately 0.1 atom% and for
quantification it is 0.2 atom%. XPS spectra were collected and
referenced to elemental standards. The Ti 2p
and O 1s
binding energy shifts of 458.6 eV and 530.1 eV match exactly
literature values for TiO
In the sample exposed to UV light
just prior to measurement there was a small shoulder to both
the Ti and O peaks that correspond to Ti
. Interestingly the
silver 3d
XPS showed a single environment centred at
367.8 eV which gave a best match for Ag
O (literature reports
at 367.7–367.9 eV) rather than for silver metal 368.3 eV
(Fig. 6).
Hence the XPS is consistent with the silver being
oxidised as Ag(I) rather than a metallic form in the thin films.
Furthermore sputtering studies showed no change in the silver
environment with sputter depth. This indicates that the silver is
present as Ag
O and not a Ag
O coated Ag particle; as
otherwise an asymmetry to the peak shape would have
UV-vis spectroscopy of the TiO
and Ag–TiO
thin films on
glass was carried out in the range 300–800 nm. A band edge for
the O
to Ti
transition in anatase TiO
was observed in all
of the types of coating at approximately 380 nm. This coupled
with XRD and Raman evidence showed that the anatase form
of TiO
was present in all films. An approximate value of the
optical band gap for the coatings was obtained by extrapola-
tion on a plot of (ahn)
versus hn, where ais the absorbance of
Fig. 4 SEM image of two coat Ag–TiO
coating 6160 000, scale bar
100 nm.
Fig. 5 SEM image of TiO
coating 6400 000, scale bar 10 nm.
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, 2007, 17, 95–104 This journal is ßThe Royal Society of Chemistry 2007
the film (a=2log T/T
;T, sample optical transmission; T
substrate optical transmission) and hnthe photon energy. The
band gap for the TiO
coating was in the region of 3.0 eV—
which is to be expected for the anatase form of TiO
(3.2 eV).
Band gap plots for the Ag-doped coatings were not as
easy to interpret as that of TiO
, giving a band gap range of
2.8–3.4 eV. Ag metal nanoparticles could not be detected by
the observation of a plasmon band
in the UV visible
spectra of the Ag–TiO
films. However, nanoparticulate silver
was detected in the initial starting sol by this method,
exhibiting a broad plasmon band at 430 nm. There was,
therefore, considering the UV, XAS and XPS spectra, little
evidence for the incorporation of these Ag metal nanoparticles
into the coatings intact without transformation into an oxide.
Functional properties I: photocatalysis and water droplet contact
All of the films showed photocatalytic activity with 254 nm
germicidal lamp illumination over a period of eight hours. The
reason for choosing the 254 nm (4.88 eV) lamp was to make
sure that the radiation was of greater energy than the TiO
band gap (3.2 eV). The degree of photocatalysis observed
varied between the different coatings, as shown in Fig. 7. It can
be clearly seen that the Ag-doped coatings were significantly
more photocatalytically active than the undoped TiO
of the same thickness. Amongst the different thickness
Ag-doped coatings there was also a difference in the
photocatalytic activity. The two-coat Ag–TiO
film had the
highest initial rate of photocatalysis. The zero order rate
constants for the degradation of stearic acid were calculated at
4.05 610
molecules cm
for TiO
and 5.85 6
molecules cm
for a Ag
coating of the
same thickness. The photoactivity of the TiO
films generated
in this study to photomineralise stearic acid was slightly lower
than our previous work using CVD and sol–gel prepared
In previous work depositions had been conducted on
barrier glass which has a diffusion layer to stop sodium ion
diffusion from the glass substrate into the film. It has been
noted previously that sodium diffusion during calcinations can
reduce the photocatalytic ability of titania films.
our XPS and WDX studies did not detect any sodium in the
titania films so if present it must be less than the 0.1 atom%
detection limit of these techniques.
Initial water contact angle measurements showed that all of
the samples were hydrophilic as they made ca.15uwater
contact angles and they became superhydrophilic upon
exposure to UV radiation. The Ag–TiO
samples had contact
angles of around 1uafter only the initial 30 min of irradiation
with 254 nm. These angles decreased further upon subsequent
exposure to the germicidal lamp (254 nm)—but as they were so
low they were difficult to quantify. However, it showed that
the 2-coat Ag–TiO
film had a very high degree of
photoinduced superhydrophilicity, as did the three and four
coat versions of the same coating. Photoinduced super-
hydrophilicity was not observed in the coatings deposited
onto metal substrate materials, with initial contact angles
being significantly higher (ca.20u) than for equivalent coatings
on glass. This may be due to metal ions diffusing into the
coating during the annealing step.
Functional properties II: microbicidal activity
The antimicrobial activity of the coatings was assessed against
three different micro-organisms; Staphylococcus aureus (NCTC
6571), Escherichia coli (NCTC 10418) and Bacillus cereus
(CH70-2). These organisms represent a spectrum of different
classes of bacterium. S. aureus is perhaps the most important
target for this investigation, because of its direct link with MRSA
and hospital acquired infections. S. aureus is also a fairly typical
example of a Gram-positive organism, so it serves as a useful
indicator of the behaviour of a sample coating towards this class
of micro-organism. In the interests of completeness and
experimental rigour, the coatings were also tested against E.
coli, a Gram-negative organism and with B. cereus,aGram-
positive spore-forming organism. It should be noted that the
same coatings were reused for all antimicrobial testing and that
all experiments were carried out in duplicate and repeated twice.
The samples were cleaned between uses by wiping with
isopropanol wipes (as commonly used to clean hard surfaces in
hospitals). The Ag-doped coatings performed very well under
conditions of reuse, maintaining a constant level of effectiveness
despite being handled, cleaned and reused.
Staphylococcus aureus (NCTC 6571). Experiments with
S. aureus were carried out on timescales of two hours, four
Fig. 6 XPS Ag 3d profile for a four coat Ag–TiO
Fig. 7 Relative photocatalytic abilities of all coatings.
This journal is ßThe Royal Society of Chemistry 2007
J. Mater. Chem.
, 2007, 17, 95–104 |101
hours and six hours. Both the Ag-doped and un-doped TiO
coatings displayed antibacterial activity towards S. aureus,
although to varying degrees (Fig. 8). The two-coat Ag–TiO
coating proved to be extremely effective against S. aureus.
After six hours of illumination under 365 nm UV radiation the
two coat Ag–TiO
coating proved to be 99.997% effective
against an inoculum of approximately 2.15 610
cfu ml
(colony-forming units ml
)S. aureus. As a point of reference,
the analogous TiO
coating displayed an effectiveness of
49.925% against the same inoculum. Supplementary studies
carried out at four and two hours of illumination enabled
elucidation of relative antimicrobial activity between coating
types, and also of the relationship between UV light dose and
antimicrobial activity.
Escherichia coli (NCTC 10418). Six hour experiments were
carried out with the two coat Ag–TiO
coating against E. coli.
The results were not as striking as with S. aureus, but
nonetheless revealed that the coatings exerted an antimicrobial
effect. The coating averaged an effectiveness of 69% against an
inoculum of ca. 2.61 610
cfu ml
E. coli. The coating was
noticeably less effective against E. coli than S. aureus, even
though the size of the inoculum was similar.
Bacillus cereus (CH70-2). The two-coat Ag–TiO
was also tested against B. cereus, another Gram-positive
organism, but one that forms spores under adverse environ-
mental conditions. Four and two hour experiments were
carried out against this organism using the two coat Ag–TiO
coating only. The coating achieved greater than 99.9% kills of
this organism at both 2 h and 4 h exposure periods with 365 nm
UV. It should be noted however, that this was from an initial
concentration of ca. 1.0 610
cfu ml
B. cereus. Further, the
UV light control L+S2showed no measurable kill at 2 h and a
64% kill at 4 h of exposure. This demonstrates that the coating
is extremely effective after just 2 h against an inoculum in the
region of one hundred million cfu ml
. This level of
contamination is still significantly greater than what would
be found on a contaminated surface. For example, S. aureus
contamination of a surface was shown typically to be between
4 and 7 cfu cm
There are a number of avenues that can be followed in an
attempt to provide an explanation for the enhanced activity of
the Ag-doped TiO
coating over that of an un-doped TiO
film. In reality, there is likely no one single reason for the
increased activity, rather the observation results from a
combination of effects. The simplest explanation is one of
surface microstructure. The Ag-doped films displayed islands
with a high silver density. This in itself is a good explanation
for the difference in activities, but it does not take into account
other evidence from the characterisation of the coatings. XRD,
XPS and XANES analysis elucidated the presence of the silver
oxide Ag
O. It is possible that these species act as a source of
electrons and as charge separators because of their high
electron density relative to the TiO
matrix. These factors
would enhance the overall photoactivity of the coating by
firstly donating extra electrons to the conduction band which
in turn are able to produce more reactive species at the catalyst
surface, and secondly by blocking electron–hole recombination
which stops the production of radicals at the surface. Indeed,
this explanation is supported by the photocatalysis results.
There have also been reports in the literature of some silver
oxides exhibiting semiconductor behaviour
and Ag
quoted in the literature as having a band gap of 2.25 eV
(550 nm).
This may go some way to explaining the apparent
change in the optical band gap of the Ag–TiO
films over the
It is difficult to compare photocatalysis results with the
literature since there is not as yet an agreed universal reference
against which photocatalysis can be measured. However, the
use of Pilkington Activ2glass (which is TiO
coated) as a
reference photocatalyst has been proposed, since this would
make a reliable standard.
Preliminary photocatalytic results
in our laboratory indicate the Ag–TiO
films are considerably
more active. It is equally difficult to compare the micro-
biological results of this investigation with other work in the
literature because of the great diversity in techniques used, and
in the precise details of the experiments performed. The vast
majority of studies of TiO
antimicrobials are carried out in
solution using a suspension of Degussa P25 TiO
This is
fundamentally different from the thin film coatings prepared in
this study because the surface area of active catalyst in
suspension would be significantly greater than that available
on a thin film surface (perhaps up to 10 000 times greater).
Furthermore, titania particles in suspension can be ingested by
cells via phagocytosis—this has been shown to cause rapid
cellular damage in addition to that caused by photocataly-
Consequently, literature results from this method differ
greatly from those obtained in this study. Most studies also
examined only E. coli. However, the efficacy against E. coli
when using a suspended powder is variable from study to
study. One study used an inoculum of 1 610
cfu ml
E. coli
in a P25 suspension and observed 85% effectiveness after 20 min
exposure to UV (peak wavelength 356 nm), and 100%
effectiveness after an hour.
This compares with 69%
Fig. 8 Bacterial kills for the two coat Ag–TiO
sol–gel prepared
coating against Staphylococcus aureus after 2, 4 and 6 h illumination
times with 365 nm radiation. The viable counts are expressed as
colony-forming units ml
. L+S+ refers to the exposure of an active
coating (identity in brackets) to UV light. L+S2refers to the exposure
of an uncoated slide to UV light. L2S+ refers to an active coating
(identity in brackets) kept in the dark and L2S2refers to an uncoated
slide kept in the dark.
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J. Mater. Chem.
, 2007, 17, 95–104 This journal is ßThe Royal Society of Chemistry 2007
effectiveness against 1 610
cfu ml
E. coli after 6 h UV
illumination (365 nm) for the two-coat Ag–TiO
prepared in this study.
The antimicrobial effect of titania coatings is derived from
the production of hydroxyl radicals,
hence a rationalisa-
tion for the relative effectiveness of the coating against Gram-
positive and Gram-negative organisms can be offered.
Previous research examining the toxicity mechanism of TiO
against micro-organisms showed that the lethal action
involved breach of the cytoplasmic membrane and the
resultant leakage of intracellular components.
For this to
occur, the hydroxyl radicals produced at the coating surface
must be able to directly attack the cytoplasmic membrane. The
differing morphologies of Gram-positive and Gram-negative
cell envelopes means that the passage of hydroxyl radicals
from coating surface to cytoplasmic membrane is hindered to
differing extents. For S. aureus, the only barrier is the
peptidoglycan layer and the periplasmic space. Despite having
a thick layer of peptidoglycan, S. aureus is likely afforded little
protection from the hydroxyl radicals. This is because the
peptidoglycan is composed of a fairly open network polymer
of N-acetylmuramic acid and N-acetylglucosamine polysac-
charide chains, with peptide bridges. In contrast, the passage
of hydroxyl radicals towards the cytoplasmic membrane of
E. coli is significantly hindered by the morphology of the cell
envelope. In Gram-negative organisms, such as E. coli, the
cytoplasmic membrane is protected by a thin layer of
peptidoglycan, followed by an outer membrane. The outer
membrane presents a significant barrier to hydroxyl radical
passage since it is comprised of a complex layer of lipids,
lipopolysaccharides and proteins. The outer membrane layer
presents an attractive target for approaching hydroxyl radicals
because of this composition. Although the outer membrane is
semi-permeable, many of the hydroxyl radicals will react with
the lipid constituents of the membrane rather than pass
through it. Once the membrane is breached, however, there are
no further significant obstacles blocking the approach of the
radicals to disrupt the cytoplasmic membrane and cell death
can be observed.
This interpretation is supported by a recent
study of the photokilling of E. coli by TiO
thin films.
bactericidal action was found to be a two step process in which
the outer membrane is compromised first, followed by the
cytoplasmic membrane. Hence the Gram-negative envelope
affords better protection against the hydroxyl radical as a
cytotoxic agent. This rationale would therefore account for the
higher antimicrobial activity of the Ag–TiO
towards Gram-
positive organisms than Gram-negative.
In the films prepared here, no antibacterial activity was
observed from the Ag–TiO
films in the absence of light—this
implies that the silver has no direct role in promoting increased
bacterial kills. The presence of silver as an oxide within the film
enhanced the antimicrobial and photocatalytic properties.
Solutions of silver sols have applications as antibacterial
agents where the active component of these solutions is the
ions which disrupt bacterial metabolism.
The silver sols
display a large surface area and are known to be partially
oxidised by atmospheric oxygen to give Ag
O. While this is
only sparingly soluble in water it is sufficient to provide
antibacterial effects. These antibacterial effects are manifested
independently of whether a light source is used or not. In the
films made in this study no bacterial kill was observed in the
dark. This is strong evidence that the films are not functioning
as microbicides due to the presence of silver ions, as we would
have observed some kill in the absence of light. Silver metal is
normally quite resistant to oxidation in air and requires
stronger oxidising agents such as ozone to convert to the oxide.
The fact that the silver is present as Ag
O in these films is a
consequence of the high temperature anneal and the fact that
the silver is embedded in a titanium dioxide matrix. Although
the silver is present as the oxide, UV illumination of titania can
in principle convert this to the native metal in the presence of
titanium dioxide. However XPS studies of the Ag
both before and after UV irradiation did not show any change
in the silver environment—the binding energy shifts match well
for Ag
O and no lower energy peak was seen as would be
characteristic of silver formation. Hence this combined with
the lack of any antibacterial activity in the dark seems, even
after 12 cycles of UV irradiation, to indicate that any possible
formation of silver metal in this system occurs below the
detection limits of the experiments used. Recent work has
shown that at elevated temperature in the presence of oxygen
the most stable thermodynamic form is Ag
This correlates
nicely with what was observed in this study. However, the
presence of the silver oxide Ag
O in conjunction with titania
did show a marked enhancement over a pure titania film as a
photocatalyst. This is most likely due to stabilisation of
photogenerated electron–hole pairs at the titania surface by
localisation of the photogenerated electron onto the silver
Photocatalytically-active and antimicrobially-active coatings
were synthesised by a simple sol–gel dip-coating technique.
The resultant coatings were characterised by glancing angle
X-ray diffraction, XPS, XANES, Raman spectroscopy, SEM,
WDX and UV-vis spectroscopy and shown to consist of
anatase titania with embedded Ag
O particles. Photocatalytic
activity of the coatings was determined by photomineralisation
of stearic acid and monitored by FT-IR spectroscopy.
Coatings demonstrating high photocatalytic activity against
stearic acid were then screened for antibacterial efficacy
against Staphylococcus aureus (NCTC 6571), Escherichia coli
(NCTC 10418) and Bacillus cereus (CH70-2). Ag-doped
coatings were found to be significantly more photocatalytically
and antimicrobially active than a regular TiO
coating. This
was explained in terms of a charge separation model. Notably
the coatings showed no activity against bacteria in the dark—
indicating that their efficacy is not due to silver ions acting as a
microbicide. The coatings also demonstrated significantly
higher activity against the Gram-positive organisms than
against the Gram-negative. This was explained in terms of
the comparative morphologies of the cell envelopes and the
permeability of these envelopes to the likely toxic agent, the
hydroxyl radical. The two coat Ag–TiO
coating would appear
to be a potentially useful coating for hard surfaces in a hospital
environment due to its robustness, stability to cleaning and
reuse, and its excellent antimicrobial response to all organisms
This journal is ßThe Royal Society of Chemistry 2007
J. Mater. Chem.
, 2007, 17, 95–104 |103
tested thus far. Such a coating would need to be applied at the
point of manufacture of a particular item—and could not be
retrofitted to existing surfaces because of the heat treatment
required to generate the active coatings. However on new
products it could create a very potent antimicrobial coating.
The Horshall fund is thanked for financial support. Professor
Parkin is a Royal Society Wolfson Trust merit holder. K.P.
would like to thank Ms Vale´rie Decraene for her help and
advice during the antimicrobial testing. Mr Kevin Reeves is
thanked for his assistance with SEM imaging and WDX
analysis. CCLRC Daresbury is thanked for provision of
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... Depending on their reactivity with the host matrix, dopants can be used to modify the electrical and optical properties of polymers. Although considerable research on charge carrier transport and optical characteristics of doped polymers has been published [31][32][33][34][35][36][37]. ...
composite silver nanoparticles were synthesised using melanin broth and Arabic gum as a reducing and binding agent. The reactions are carried out with water because it is a non-hazardous solvent. The produced composites either had specified diameters (average diameter of 50 nm) with high silver loading or lower loading composites with tuneable morphologies and electrical properties. UV-IR, gamma, and conventional light are used to characterise the synthesised composite silver nanoparticles. Furthermore, measurements are carried out of the dielectric constant, refractive index, energy gap, optical and electrical conductivities, and refractive index coefficients. The silver nanoparticle formation was validated by UV-Vis measurement of the sample, which demonstrated a distinct peak at a wavelength of 420 nm. The characteristics of the composite silver nanoparticles are also quantified using several methods, including XRD, SEM, and particle size analysis.
... Furthermore, researchers also developed photocatalysts where TiO 2 is coated on the surface of glasses, ceramics and metal plates by sol-gel process [22][23][24][25]. However, TiO 2 easily peels off from the substrate during applications. ...
Direct application of TiO2 nanopowder in water remediation is hindered due to sophisticated separation of the photocatalyst. Therefore, alternative partially crystallized porous glass based photocatalysts were prepared on the basis of combined phase separation and partial crystallization of 55.4SiO2–23B2O3–7Na2O-14.6TiO2 (mol.-%) initial glass composition followed by selective leaching. The advantage of this glass composition is that, 3-D shaping is possible via selective laser sintering technique. Therefore, various macroscopic shapes were fabricated via selective laser sintering and conventional techniques and their resulting properties and photocatalytic activities were compared. Selective laser sintered glasses contain slightly less content of anatase phase due to formation of rutile during sintering process as opposed to conventional glasses. Textural properties are similar in both selective laser sintered and conventional shaped glasses which indicate similar phase separation mechanism and microstructure. In terms of macroscopic shapes, photocatalytic activity increases in the order: monolith < granulate < “macropowder” due to increase in the surface area to volume ratio. The photocatalytic activity is mainly determined by the amount of the anatase phase, thus conventional glasses exhibit slightly higher activity than selective laser sintered glasses.
... Morphological differences of the outer layers affect bacterial interaction with NMNSs, thus leading to differences in the antibacterial effect. Moreover, the nanometer size of metal particles increases their liability to adhere to a cell membrane (Page et al. 2007). The porous structure of the particles could promote sorption of the bacteria onto their surface due to their large surface area, which increased the chance for the antimicrobial metallic nanoparticles to contact the bacteria and then damaged and altered their functionality (Xia et al. 2011). ...
In this work, magnetic activated carbon was investigated to remove the antibiotic cefazolin from aqueous solutions as well as its antibacterial properties. To determine the optimal process conditions and achieve maximum efficiency, the effect of pH, temperature, contact time, initial concentration of the drug and composite dosage, using the response surface method and the central composite design model was investigated by the design of experiments software. Structural characteristics and morphology of the nanocomposite were analyzed by using FTIR, XRD, EDAX, SEM, TEM, BET, TGA, and VSM analyses. The results showed that pH = 6, the temperature of 30 °C, contact time of 150 min, initial concentration of drug 20 mg/l, and composite dosage of 0.03 g were the best conditions for removing cefazolin from aqueous solution. In these conditions, the magnetically activated carbon was able to remove 96% of cefazolin. The Langmuir, Freundlich, and Temkin isotherms were also studied, and the results showed that the absorption behavior is most consistent with the Langmuir isotherm. The results of thermodynamic experiments also showed that the adsorption process is exothermic and spontaneous. Finally, the antibacterial properties of the prepared nanocomposite on Streptococcus and Salmonella were investigated and the results showed that the prepared sample has antibacterial properties.
... The visible light absorbance and photocatalytic activity of TiO 2 could be enhanced by metal doping (Gelover et al., 2006) and provide UV irradiation (Yamashita et al., 2001), respectively. Different studies proved that the bacterial inactivation by photocatalysis could be improved by silver doping of TiO 2 (Page et al., 2007;Pratap Reddy et al., 2007). Another study reported that polyvinyl chloride nanocomposite on silver metal doping with TiO 2 nanoparticles showed efficient antibacterial activities (Cheng et al., 2006). ...
Food is an inevitable part of our daily life. Food that is rich in carbohydrates, proteins, and fats is the cornerstone of a healthy diet. These foods are subjected to easy deterioration by both biological and environmental factors. Hence, packaging plays an important role in keeping food preserved and devoid of spoilage. Food packaging has made an era of change from conventional composites to currently used bionanocomposites. Bionanocomposites are nanomaterials having an inorganic moiety coated with a biopolymer. These types of food packaging systems are ideally preferred as it protects the food from microbial attack and prevents the spoilage of food, thereby increasing its shelf life. This chapter emphasizes the trends followed in food packaging systems from the conventional packaging systems to bionanocomposites.
... Titanium (Ti) and its alloys are the most commonly used materials for orthopedic and dental implants due to their good mechanical properties, corrosion resistance, and biocompatibility [21]. Additionally, titanium dioxide is a well-known nontoxic photocatalytic material that can perform as an antimicrobial agent due to the photocatalytic processes occurring on the surface of TiO 2 when irradiated with UV light [22,23]. However, biofilm formation remains a critical factor for implant-associated infections which are the leading cause of implant failure [24,25]. ...
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Metal-based nanoparticles with antimicrobial activity are gaining a lot of attention in recent years due to the increased antibiotics resistance. The development and the pathogenesis of oral diseases are usually associated with the formation of bacteria biofilms on the surfaces; therefore, it is crucial to investigate the materials and their properties that would reduce bacterial attachment and bio-film formation. This work provides a systematic investigation of the physical-chemical properties and the antibacterial activity of TiO2 thin films decorated by Ag and Au nanoparticles (NP) against Veillonella parvula and Neisseria sicca species associated with oral diseases. TiO2 thin films were formed using reactive magnetron sputtering by obtaining as-deposited amorphous and crystalline TiO2 thin films after annealing. Au and Ag NP were formed using a two-step process: magnetron sputtering of thin metal films and solid-state dewetting. The surface properties and crystallo-graphic nature of TiO2/NP structures were investigated by SEM, XPS, XRD, and optical microscopy. It was found that the higher thickness of Au and Ag thin films results in the formation of the en-larged NPs and increased distance between them, influencing the antibacterial activity of the formed structures. TiO2 surface with AgNP exhibited higher antibacterial efficiency than Au nanostructured titania surfaces and effectively reduced the concentration of the bacteria. The process of the observation and identification of the presence of bacteria using the deep learning technique was realized.
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Et ve et ürünleri üretiminin, çiftlikten çatala tüm zincirlerde (üretim, işleme, nakliye ve tüketici aşaması) çevre üzerinde olumsuz etkisi bulunmaktadır. Et endüstrisinde, kesim ve etin ileri ürünlere işlenmesi sırasında kan, kemik, deri, iç organlar, boynuzlar, ayaklar gibi büyük hacimlerde yan ürünler çıkar. Kesim atıkları, insan veya hayvan sağlık risklerine göre Avrupa Birliği ülkelerinde yüksek riskli, orta ve düşük riskli olmak üzere üç kategoride sınıflandırılır. Bu atıkların ve yan ürünlerin ekolojik olarak işlenmesi veya imha edilmesi çevre koruma açısından önemlidir. Et işleme zincirlerinde yan ürünlerin değerlendirmesine yönelik yenilikçi yaklaşımlar geliştirilmektedir. Kesimhane yan ürünleri zengin protein, yağ, vitamin, mineral kaynağı olduğu için yüksek besin değerine sahiptir ve birçok ülkede geleneksel olarak gıda veya gıda bileşenleri olarak tüketilmektedir. Proteinlerin jelleşme, köpürme ve emülsifikasyon gibi teknolojik kullanımları bulunmaktadır. Protein hidrolizatları sindirilebilirlik, lezzet, antihipertansif, antioksidan, antitrombotik ve antimikrobiyal etkiye katkıda bulunabilir. Yağlar ise kozmetik endüstrisinde, hammadde olarak biyodizel üretiminde, plastiklere alternatif olabilecek biyolojik olarak parçalanabilen plastiklerin geliştirilmesinde kullanılabilir. Mineral olarak zengin (fosfor ve kalsiyum gibi) kesim attıkları, evcil hayvan yemleri, gübre olarak kullanılır. Karaciğer, demir ve çinko gibi çeşitli mikro besinlerin kaynağıdır. Ayrıca kan, demir eksikliği olan kişiler için ek olarak kullanılabilecek iyi bir heme demir kaynağıdır ve bir polipeptit ile ilişkilendirilmesi durumunda demir emilimini arttırdığı rapor edilmiştir. Kesim atıklarından tıbbi açıdan önemli olan birçok madde elde edilir ve deri gibi bazı kısımlar yanıklar ve ülserler için pansuman olarak kullanılır. Deri endüstrisinde kesim atıkları kullanılarak birçok ürün üretilmektedir. Bu derlemede kesim atıklarının değerlendirilmesi hakkında bilgi vermek ve et ürünlerin üretimini daha sürdürülebilir hale getirme fırsatlarını tartışmak amaçlanmıştır. Sürdürülebilir et ve et ürünleri ile ilgili yeni uygulamalara özellikle su ve enerji tüketiminin çevresel etkilerinin azaltılması, gelecekteki çalışma önerisi olarak sunulabilir.
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Antibacterial Materials
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The new precursors [Ti(OPri)3(OCH2CH2NMe2)] 1 and [Ti(OPri)2(OCH2CH2NMe2)2] 2 have been prepared and characterised. Compound 1 exists in solution at room temperature as a mixture of monomer and dimer(s), however at elevated temperatures the monomer predominates. Compound 2 exists in solution predominantly as a monomeric complex presumably with pseudo-octahedral coordination at the metal centre. Thin films of TiO2 have been deposited at 300-450C by liquid injection MOCVD using both 1 and 2. Analysis of the films by Auger electron spectroscopy failed to detect nitrogen although trace carbon was detected at levels of between 2.9 and 7.7. The potential utility of these modified compounds as precursors to TiO2 is discussed.
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Surface plasmons are waves that propagate along the surface of a conductor. By altering the structure of a metal's surface, the properties of surface plasmons—in particular their interaction with light—can be tailored, which offers the potential for developing new types of photonic device. This could lead to miniaturized photonic circuits with length scales that are much smaller than those currently achieved. Surface plasmons are being explored for their potential in subwavelength optics, data storage, light generation, microscopy and bio-photonics.
Coulometric titration and conductivity measurements indicate that the nonstoichiometry of Ag2+δO is due to neutral oxygen vacancies, VxO, and to a smaller extent to VO. Defect concentrations in the bulk phase are estimated. The role of a nonstoichiometric semiconducting oxide surface layer is discussed for the primary steps in ethylene oxidation catalysis.Aspects of further studies on defect chemistry of catalyst surfaces with solid state electrochemical methods are raised.
In the context of studying the feasibility of photocatalytically self-cleaning windows and windshields, clear, abrasion resistant, photocatalytic films of TiO2 were formed on soda lime glass and on fused quartz by a sol-gel process. The rate of photooxidation of contaminant deposits was estimated by measuring the rate of decrease in the integrated IR absorbance associated with the C-H stretching vibrations of a thin solution-cast film of stearic acid under 365 nm (2.4 mW/cm2) or 254 nm (0.8 mW/cm2) irradiation. Approximately 3 × 10−4 stearic acid molecules were stripped per 365 nm photon in either front- or back-illuminated soda lime glass, and 6 × 10−4 molecules when the films were coated on fused quartz. For thin TiO2 films on fused quartz, the rate of photooxidation, normalized by the number of photons absorbed per unit area, was independent of the wavelength. In contrast, for films on soda lime glass, the rate of photooxidation, when similarly normalized, was higher for the less penetrating wavelength. The reduced photoactivity on glass at the deeply penetrating wavelength (365 nm), as well as the greater photoefficiency on quartz than on glass, are attributed to diffusion of sodium oxide from the glass into the inner glass-contacting zone of the TiO2 layer.
Scientific studies on photocatalysis started about three decades ago. Titanium dioxide (TiO2), which is one of the most basic materials in our daily life, has emerged as an excellent photocatalyst material for environmental purification. In this short account, we will briefly discuss some fundamental studies on TiO2 photocatalysis, summarize the present commercialization of TiO2-based products, and highlight several points for the future development of TiO2 photocatalysis. To cite this article: A. Fujishima, X. Zhang, C. R. Chimie 8 (2005).
The interest in heterogeneous photocatalysis is intense and increasing, as shown by the number of publications on this theme which regularly appear in this journal, and the fact that over 2000 papers have been published on this topic since 1981. This article is an overview of the field of semiconductor photocatalysis : a brief examination of its roots, achievements and possible future. The semiconductor titanium dioxide (TiO 2 ) features predominantly in past and present work on semiconductor photocatalysis; as a result, in the most of the examples selected in this overview to illustrate various points the semiconductor is TiO 2 .
We report the novel concept of photochemical sterilization. Microbial cells were killed photoelectrochemically with semiconductor powder (platinum-loaded titanium oxide, TiO2/Pt). Coenzyme A, (CoA) in the whole cells was photo-electrochemically oxidized and, as a result, the respiration of cells was inhibited. Inhibition of respiratory activity caused death of the cells. Lactobacillus acidophilus, Saccharomyces cerevisiae and Escherichia coli (103 cells/ml respectively) were completely sterilized when they were incubated with TiO2/Pt particles under metal halide lamp irradiation for 60–120 min.
Acidification of an isopropanol solution containing mixtures of [Ti(OPri)4] and [W(OEt)5] produced solutions from which various TiO2, WO3 and TiO2/WO3 thin films could be obtained by dip coating and annealing. The films were analysed by X-ray diffraction, SEM/EDAX, Raman, electronic spectra, contact angle and photoactivity with respect to destruction of an over layer of stearic acid. The TiO2/WO3 films were shown to be mixtures of two phases TiO2 and WO3 rather than a solid solution TixWyO2. The 2% tungsten oxide doped titania films were shown to be the most effective photocatalysts. All of the TiO2 and TiO2/WO3 films showed light induced superhydrophillicity.
When illuminated by near-UV light, titanium dioxide (TiO2) exhibits excellent bactericidal activity. However, there exist some different mechanisms for cell killing via photocatalysis. In the present study, the photocatalytically bactericidal mechanism of TiO2 thin films was investigated by atomic force microscopy (AFM) in conjugation with some other techniques. The decomposition process of the cell wall and the cell membrane was directly observed by AFM for the first time. The resultant change in cell permeability was confirmed by potassium ion (K+) leakage. Quantum dots (QDs) were designed originally as a probe to examine the cell permeability for macromolecules. The corresponding bactericidal activity of TiO2 thin films was examined by cell viability assay. These results suggested that the cell death was caused by the decomposition of the cell wall and the cell membrane and the resultant leakage of intracellular molecules.
Polypropylene/silver composites were subjected to silver ion release experiments in order to investigate their Ag+ release capabilities, a pertinent condition for antimicrobial efficacy. Polypropylene containing elementary silver powder having a specific surface area of 0.78 m2/g was considered as the principal antimicrobial filler. In addition the effectiveness of other commercial antimicrobials based on silver were also examined. Evidence is presented for the release of silver ions from these composites in an aqueous environment. The silver ion release depends on the nature of the antimicrobial filler and the polymer matrix. Scanning electron microscopy has been employed to investigate the morphology of the composite and they were found to be active against the microbes. An excellent correlation between the silver ion release experiments and the antimicrobial efficacy was found. Multifilament yarns produced from polypropylene containing elementary silver powder show excellent long term Ag+ release properties.