Journal of Biomaterials and Nanobiotechnology, 2012, 3, 421-430
http://dx.doi.org/10.4236/jbnb.2012.34042 Published Online October 2012 (http://www.SciRP.org/journal/jbnb)
421
Synergistic Antibacterial Performance of a Cu/WO3-Added
PTFE Particulate Superhydrophobic Composite under
Visible-Light Exposure
Yanyan Yao1,2, Kentaro Yamauchi3, Goro Yamauchi4, Tsuyoshi Ochiai1,5, Taketoshi Murakami 1,
Yoshinobu Kubota2
1Kanagawa Academy of Science and Technology, Kawasaki, Japan; 2Department of Urology and Molecular Science, Graduate
School of Medicine, Yokohama City University, Yokohama, Japan; 3 Collaborative Research Centre, Daido University, Nagoya,
Japan; 4Department of Information Design, Daido University, Nagoya, Japan; 5Division of Photocatalyst for Energy and Environ-
ment, Tokyo University of Science, Tokyo, Japan.
Received August 13th, 2012; revised September 30th, 2012; accepted October 14th, 2012
ABSTRACT
Addition of TiO2 to a polytetrafluoroethylene (PTFE) particle-dispersed composite contributes to the self-cleaning
properties of the water-repellent composite. However, its application is limited to outdoor usage or under ultraviolet
(UV) irradiation. In this study, a novel visible-light-sensitive photocatalytic and superhydrophobic material was devel-
oped by adding Cu/WO3 to a PTFE particulate composite material to overcome this deficit. A remarkable property of
this novel composite material is the synergistic antibacterial performance against Escherichia coli (E. coli), Staphylo-
coccus aureus, and methicillin-resistant Staphylococcus aureus compared with the addition of Cu/WO3 without PTFE
particles material. During 24-h exposure in visible light at 2000 lx, the number of viable cells of the three strains on the
surface of the 8 wt% Cu/WO3-added PTFE particulate composite decreased from 2 – 4 × 105 colony-formation units
(CFUs) to less than 10, the limit of detection. This bactericidal rate is four times higher than that of 8 wt% Cu/WO3
without PTFE particles material, which is attributed to the air trapped in the rough surface of the novel material provid-
ing additional oxygen to the photocatalytic reaction. Even for exposure to visible light at 100 lx, the decrease in CFUs
of E. coli on the 12 wt% Cu/WO3-added PTFE particulate composite reached nearly 2.0 logs. The characterization of
the Cu/WO3-added PTFE particulate composite indicated that the composite material containing 80 wt% PTFE main-
tained a superhydrophobic or water-repellent property with a water contact angle >150˚, although the Cu/WO3 in the
composite material remained hydrophilic under visible light. The Cu/WO3-added PTFE particulate composite displayed
photocatalytic reactions to decompose oleic acid adsorbed on its surface and gaseous acetaldehyde under UV-A and
visible-light illumination. All results demonstrate that the Cu/WO3-added PTFE particulate composite material may be
used in sterilization, as a water repellent, for self-cleaning, and in the oxidative decomposition of volatile organic com-
pounds (VOC) both indoors and outdoors.
Keywords: Cu/WO3 Photocatalyst; PTFE-Hydrophobicity; Particulate-Composite; Synergistic Antibacterial
Performance; Escherichia coli; MRSA
1. Introduction
The conventional superhydrophobic surface associated
with polytetrafluoroethylene (PTFE) [1,2] provides no
sterilization performance. This limits its application in
the field of disinfection. Also, a crucial and unavoidable
problem in the commercialization of this superhydropho-
bic surface is that it is not sufficiently repellent against
organic liquids, and this results in a lack of durability. In
order to obtain a superhydrophobic surface exhibiting not
only water repellency but also self-cleaning performance,
a material that combines TiO2 nanoparticles with PTFE
can be used [1,3]. TiO2 photocatalysis has been used to
inactivate various bacteria, such as Escherichia coli (E.
coli), methicillin-resistant Staphylococcus aureus (MRSA),
Pseudomonas aeruginosa (P. aeruginosa), Legionella
pneumophila (L. pneumophila) [4,5], and Clostridium
difficile spores [6]. The inclusion of TiO2 in a PTFE
coating is expected to generate antimicrobial and self-
cleaning properties, which would expand its scope of
application. However, such a composite material could
not play a full role indoors under fluorescent and incan-
descent light exposure, because these types of light emit

Synergistic Antibacterial Performance of a Cu/WO3-Added PTFE Particulate Superhydrophobic
Composite under Visible-Light Exposure
422
little UV radiation. Accordingly, the development of
powerful visible-light-sensitive photocatalysts, such as
lattice-doped TiO2 [7,8] and WO3 [9-12] using various
dopants, has become a popular area of research.
In recent years, Cu/WO3 has attracted a great deal of
attention because it shows a relatively stronger oxidative
power under exposure to visible light (>400 nm). In the
current study, a water-repellent composite material with
a significant antibacterial effect and self-cleaning per-
formance has been developed by the addition of Cu/WO3
to a PTFE particulate composite material. The novel
composite material is expected to be useful both outdoors
and indoors. The surface characteristics of the newly
developed composite are examined in this paper. The
antibacterial activities of the composite against gram-
negative E. coli, gram-positive Staphylococcus aureus (S.
aureus), and MRSA are also evaluated under visible-
light irradiation with intensities ranging from 100 to
2000 lx, which is equivalent to indoor and outdoor con-
ditions. Furthermore, the photocatalytic decomposition of
oleic acid adsorbed on the surface and gaseous acetalde-
hyde using the Cu/WO3-added PTFE particulate compos-
ite material were examined under UV-A and visible-light
illumination.
2. Materials and Methods
2.1. Preparation of Hydrophobic Composite
Material
Cu/WO3 used in this study is HP-CW091, which was
developed as part of the New Energy and Industrial
Technology Development Organization (NEDO) Project,
“Photocatalytic industry emerging project in pursuit of a
environmental society”. The composite material sample
was prepared by the addition of Cu/WO3 at various con-
centrations (0, 3 wt%, 8 wt%, and 12 wt%) into a mixture
composed of PTFE particles, a fluorinated binder, and
fluoro-oil. This mixture together with butyl acetate was
sprayed over a substrate to form the Cu/WO3-added
PTFE particulate composite material. The PTFE particu-
late composite material formed a layer approximately 5
μm in thickness in a single spray. Particulate composite
materials with a thickness of approximately 15 μm were
formed by spraying the entire substrate three times. The
composite material was ready for contact-angle measure-
ments 24 h after the butyl acetate dried.
2.2. Characterization
2.2.1. Surface Characterization
Water contact angles were measured using an automatic
contact-angle meter (Kyowa Kaimen Kagaku CA-Z). By
using a syringe, a drop of water was deposited on the
sample. The contact angle was measured after the tip of
the needle was separated from the drop. The contact
angles measured, therefore, represented equilibrium con-
tact angles and not advancing or receding contact angles.
The contact angles were measured at five different
positions for each sample.
The surface free energy of the sample was obtained
using the following procedure. The contact angles, θSL,
of α-bromonaphthalene (79˚), methylene iodide (77˚),
and water (152˚) were substituted into the Young-Dupre
Equation:


SL LVSL
W1cos

  (1)
where WSL is the work of adhesion and λLV is the surface
free energy of the liquid as previously reported [13].
Therefore, the value of WSL may be obtained using
Equation (1).
The dispersion, polar, and hydrogen-bonding com-
ponents of WSL lead to the dispersion d
SV

, polar
p
SV

,
and hydrogen h
SV

bonding components of the surface
free energy using the Kitazaki-Hata method [13]. The
surface free energy, λSV, of the sample was obtained via
Equation (2).
dp
SVSVSV SV
hh

   (2)
2.2.2. Antibacterial Test
The bacterial activity of the Cu/WO3-added PTFE par-
ticulate composite against E. coli (NBRC 3972), S.
aureus (NBRC12732), and MRSA (clinically isolated by
the Graduate School of Medicine, Yokohama City
University) was evaluated, after some adjustments, in
accordance with the Japanese Industrial Standard me-
thods (JIS R 1702) [14]. Before testing, all water-
repellent composite samples (50 × 50 mm) were pre-
sterilized by heat treatment in an oven at 60˚C for 1 h.
The bacterial strains were cultured twice on nutrient agar
plates (Daigo, Eikenkizai, Japan) at 37˚C for 16 - 24 h.
Each strain was then, respectively, suspended in 1/500
nutrient broth (NB) solution (Daigo, Eikenkizai, Japan)
with a pH of 7.0, and diluted to approximately 106
colony-forming units (CFUs)·ml−1 to be utilized for
bactericidal tests. An aliquot (100 μL) of the bacterial
suspension (approximately 105 CFUs) was inoculated on
the sample surface. Because the test surface is hydro-
phobic, a covering quartz glass (40 × 40 mm) was
applied to disperse the suspension drip. These settings
were placed into a sealed and humid container, such as a
sterilized Petri dish, in which a sterilized moisture-
control paper filter was placed. A quartz glass (100 × 100
mm) was placed on the top of Petri dish to maximize
transmission of visible light to the surface of the sample.
The Petri dishes containing the samples were illuminated

Synergistic Antibacterial Performance of a Cu/WO3-Added PTFE Particulate Superhydrophobic
Composite under Visible-Light Exposure
423
using 20-W tubular, white fluorescent lamps (FL20SSW/
18-B; Hitachi, Japan) for 24 h. The influence of the light
intensity on the bactericidal activity was examined at 100,
300, 1000, and 2000 lx. Only the 2000 lx intensity
included light in the UV region with wavelengths less
than 400 nm at an intensity of 0.01 mW·cm−2. The light
intensity incident on the center of the specimen surface
was adjusted using a UD-40 radiometer probe head
(Topcon Corporation, Japan).
After illumination, the samples were washed with 10
mL soybean-casein digest broth including lecithin and
polysorbate 80 (SCDLP) (Daigo, Eikenkizai, Japan). The
washout solution was diluted with PBS-saline in a
10-fold dilution series. At each dilution stage, aliquots (1
mL) of the SCDLP solution were mixed with the nutrient
agar medium (14 mL) (Becton Dickinson, Franklin
Lakes, NJ, USA) at 45˚C in a 10 cm Petri dish and
allowed to cool to the room temperature. After the me-
dium solidified, the dishes were incubated at 35˚C for 24
to 48 h prior to determining the number of CFUs. The
Cu/WO3-free PTFE particulate composite films were
used as contrast samples.
Bacterial tests were conducted using three parallel
analyses for each sample, and the viable cell count was
obtained from the average value of the product of the
CFUs multiplied by 10 times the dilution rate, as shown
in Equation (3).
Viable bacterial cells = N × dilution rate × 10 (3)
where N is the number of cells of viable bacteria (CFUs)
on the Cu/WO3-added PTFE particulate composite films
after visible-light illumination for a period of time. The
value 10 indicates the solution (SCDLP liquid) volume
for sample washing. When no CFUs were observed in
undiluted SCDLP liquid, this indicated that the detection
limit was no more than 10 CFUs. In such cases, the
viable cell count was expressed as “≤10” to indicate the
detection limit. The determination of the disinfectant pro-
perty is given in terms of logarithmic decrease. In order
to investigate the key operational parameters which
affect the bactericidal activity of the composite materials,
the bactericidal tests were carried out using materials
containing various percentages of Cu/WO3, and with
different intensities of visible-light irradiation. The anti-
bacterial values, which are suitable for direct comparison,
were calculated based on these results and using Equa-
tion (4).

LL L
RlogBAlogCA 


 (4)
where L is the intensity used in the antibacterial tests, RL
is the antibacterial value, A is the number of viable
bacteria (CFUs) on the substrate surface collected im-
mediately after inoculation, BL is the number of viable
bacteria (CFUs) on the substrate surface under visible-
light irradiation for a period time, CL is the number of
viable bacteria (CFUs) on the surface of the Cu/WO3-
added PTFE particulate composite coating after visible-
light illumination for the same period of time. All viable
bacterial cell numbers (A, BL, and CL) were obtained by
using Equation (3).
2.2.3. Fluorescence Microscopy Observation
Because the viable cells were detected by the colony-
formation method which has a limitation set at no more
than 10 CFUs, green fluorescent protein (GFP) gene-
transformed E. coli (pGLO™ Bacterial Transformation
Kit, BIO-RAD) was used to investigate the complete
sterilization of the Cu/WO3-added PTFE particulate com-
posite coating. The surfaces of the samples loaded with
GFP gene-transformed E. coli were viewed by fluo-
rescence microscopy (AsioImagerA1 SP; Carl Zeiss,
Tokyo, Japan) and an image analysis system comprising
a digital counter (AxioCamMRc SP; Carl Zeiss), before
and after visible-light illumination.
2.2.4. Assessment of Self-Cleaning Performance
2.2.4.1. Degradation of Oleic Acid on Cu/WO3-PTFE
Coatings
The oxidative self-cleaning performance of the Cu/WO3-
added PTFE particulate composite coatings was assessed
by measurement of the contact angles of the composite
coatings contaminated with oleic acid (C18H34O2) during
exposure to UV-A irradiation. This was based on the
assumption that Cu/WO3-added PTFE particulate com-
posite coatings used outdoors are more susceptible to
contamination by organic pollutants and sunlight, in-
cluding strong UV light. This analysis was performed
according to the JIS R 1703-1 standard method [15].
Prior to measuring the contact angles, the samples were
cleaned for 24 h using 2 mW·cm−1 of UV-A illumination
incident on the testing surface to remove organic pol-
lutants. Next, the samples were contaminated by dip
coating (60 cm/min) with 0.5 vol% oleic acid diluted in
n-heptane. After contamination, the samples were dried
at 70˚C for 15 min, and then irradiated for 333 h using an
unfiltered UV light source (Toshiba FL10BLB; Tokyo,
Japan). The Cu/WO3-free PTFE particulate composite
was again used for contrast testing.
2.2.4.2. Degradation of Gaseous Acetaldehyde on
Cu/WO3-added PTFE Particulate Coatings
The photocatalytic decomposition performance of the
Cu/WO3-added PTFE particulate composite coatings was
evaluated by the degradation of gaseous acetaldehyde in
accordance with JIS 1701-2 [16], one of the standard me-

Synergistic Antibacterial Performance of a Cu/WO3-Added PTFE Particulate Superhydrophobic
Composite under Visible-Light Exposure
424
thods for testing air purification performance. The test
was implemented in a 500-ml sealed acrylic container by
monitoring the concentrations of acetaldehyde and CO2,
a decomposition product, under UV-A light (1 mW·cm−1)
illumination. The sample was charged into the sealed
container, and then 5 ml of standard acetaldehyde gas
(1% balanced by N2; Sumitomo Seika Chemicals Co.
Ltd., Osaka, Japan) was injected into the container. By
adsorption onto the surface of the Cu/WO3-added PTFE
particulate coating, the acetaldehyde in the container de-
creased by approximately 40 parts per million by volume
before illumination. The oxidative reaction of the ga-
seous acetaldehyde occurred by illuminating the sample
surface with a black-light blue lamp (TOSHIBA
FL10BLB, λ(p) = 310 − 380 nm, Japan) at 1 mW·cm−2 of
light intensity through a quartz window. The illumination
was initiated when the adsorption equilibrium of gaseous
acetaldehyde onto the sample surface was reached.
Meanwhile, gas concentrations were monitored using an
Innova photo-acoustic field gas monitor (Model 1412;
Innova Air Tech Instruments, Denmark). A pure PTFE
particulate composite coating without Cu/WO3 was used
as the control.
To imitate actual light conditions, the assessment of
photocatalytic degradation of gaseous acetaldehyde was
also carried out using UV-A (1 mW·cm−1) plus visible-
light (2000 lx) illumination.
3. Results and Discussion
3.1. Surface Characterization
3.1.1. Contact Angles and Surface Free Energy
The results of water contact angles and surface free
energy measurements on the surface of different com-
posites are presented in Table 1.
All PTFE particulate composite samples exhibited
contact angles exceeding 150˚, which is consistent with
their hydrophobicity despite the presence of the hyd-
rophilic Cu/WO3 photocatalyst. The contact angles of
similar materials usually lie between those of PTFE and
Table 1. Water contact angles and surface free energy of the
Cu/WO3-added PTFE particulate composite film with dif-
ferent doses of Cu/WO3. The surface free energy of the 8
wt% Cu/WO3-added PTFE particulate composite material
was 5.8 mN/m, and as low as 6.7 mN/m—for the CF3 group.
Sample Name Contac Angle
(Degree)
Surface Free Energy
(mN/m)
PTFE 152 5.0
8 wt% Cu−WO3 97 -
3 wt% of Cu−WO3-PTFE 151 -
8 wt% of Cu−WO3-PTFE 151 5.8
12 wt% of Cu−WO3-PTFE 151 -
of the binder with additives, including the hydrophilic
Cu/WO3 photocatalyst. However, the angles measured in
this study (151˚) were significantly greater than those of
pure PTFE (110˚) or binder (80˚). This is consistent with
results previously reported by Yamauchi et al. [17] and
Miller et al. [18]. In that study, a particulate composite
model was derived based on the Wenzel equation, which
takes into consideration surface roughness [19] and the
Cassie equation, which considers heterogeneous surfaces
[20]. Yamauchi concluded that the binder wets more
easily with water as compared with PTFE in PTFE
particulate composite materials. In such a system, the
contact angle increases with PTFE concentration, even
beyond the contact angle of pure PTFE. When the con-
centration of the PTFE particles dispersed in an ap-
propriate binder reached 80%, less than 78% of the
surface area between the water droplets and composite
surface was covered by air due to the surface roughness
caused by the PTFE particles. Thus, we consider that the
same tendency may be observed in the Cu/WO3-added
PTFE particulate composite materials if a part of the
binder is replaced with Cu/WO3. A similar result was
also reported by Nakajima et al. [21] in their study in
which TiO2 nanoparticles were added to superhydro-
phobic thin film. They reported that when the dose of
TiO2 nanoparticles in the film reached a concentration
below 20 wt%, the hydrophobicity of the films was not
significantly increased even after UV illumination for
800 h at an intensity of 1.7 mW·cm−2.
The surface free energy of the 8 wt% Cu/WO3-added
PTFE particulate composite material was 5.8 mN·m−1,
which was lower than that of the CF3 groups (6.7
mN· m−1) [22]. The hydrophobicity reflects the low sur-
face energy of the Cu/WO3-added PTFE particulate com-
posite coating, which is expected to make the adhesion of
contaminants difficult.
3.1.2. Scanning Electron Microscope Observation
Scanning electron micrographs of the Cu/WO3-added
PTFE particulate composite coating samples are shown
in Figures 1(a)-(c).
Figure 1(a) reveals many small spherical aggregates
of PTFE particles, indicating a heterogeneous morphol-
ogy of the pure PTFE coating. Figures 1(b) and (c) dis-
play the coating composite with 80 wt% PTFE and 3 wt%
or 12 wt% Cu/WO3, respectively. Although some ultrafine
particle aggregations are found to be embedded in the
composite coating, the surface roughness of the coating
was still maintained. Therefore, any analysis of the sur-
face wetting properties must consider the surface hetero-
geneity and surface roughness resulting from the PTFE
particles and the binder. Such an analysis has previously
been conducted by Yamauchi et al. [17], who attributed

Synergistic Antibacterial Performance of a Cu/WO3-Added PTFE Particulate Superhydrophobic
Composite under Visible-Light Exposure
425
20 kV ×10,000 1 μm 100820
(a)
20 kV ×10,000 1 μm 100820
(b)
20 kV ×10,000 1 μm 100820
(c)
Figure 1. SEM images of the Cu/WO3-added PTFE par-
ticulate composite film and the PTFE particulate composite
without Cu/WO3 film. The magnifications were ×10000. (a)
PTFE particulate composite without Cu/WO3 film; (b) 3
wt% Cu/WO3-added PTFE particulate composite film; (c)
12 wt% Cu/WO3-added PTFE particulate composite film.
The fine particles circled by white ring are Cu/WO3.
the extraordinary hydrophobicity to the presence of air
between the water droplet and the substrate surface.
3.2. Bactericidal Properties
It is well known that superhydrophobicity, or water
repellency, is not sufficient to repel organic matter. Thus,
there is potential for bacteria to adhere to the composite
more readily in ambient air. Recently, photocatalytic
inactivation has been considered as a possible approach
to overcome this shortcoming. The Cu/WO3-added PTFE
particulate composite coating as a novel visible-light-
sensitive photocatalyst containing hydrophobic materials
is expected to have a role in indoor or outdoor air puri-
fication and disinfection. Here we analyzed the bac-
tericidal properties of the Cu/WO3-added PTFE par-
ticulate composite by using the test method described in
Section 2.2.2.
Although the E. coli, S. aureus, and MRSA cells had
to be artificially attached to the surface of the Cu/WO3-
added PTFE particulate hydrophobic composite, they
could be completely inactivated by the high level of
bactericidal activity of the newly developed composite.
Figure 2(a) shows the decrease in viable E. coli cells on
the 8 wt% Cu/WO3-added PTFE particulate composite
coatings. It can be seen in the figure that under 2000 lx
visible-light illumination, the number of viable bacterial
cells decreased from 105 CFUs to a value below the de-
tection limit of the colony-formation method set at 10
CFUs. Figure 2(b) shows that the same antibacterial
performance was also confirmed on S. aureus and MRSA
by using the same samples and experimental conditions.
The data shows a possible approach to lowering the
incidence of nosocomial bacterial infection, since MRSA
is the major pathogenic organism and is resistant to many
agents [23,24]. Figure 3 displays the complete disap-
pearance of the GFP gene-transformed E. coli cells on
the composite coatings after 2000 lx visible-light was
illuminated onto the 8 wt% Cu/WO3-added PTFE par-
ticulate composite for 24 h. There is a remarkable finding
that the bactericidal activity of the Cu/WO3-added PTFE
particulate composite was significantly enhanced in
comparison with Cu/WO3 without PTFE particles coat-
ing (Figure 2).
Numerous studies have explained the mechanism of
photocatalytic antimicrobial activity as the loss of cell
membrane integrity caused by electrons/holes or by rea-
ctive oxygen species (ROSs) [25-27]. Therefore, we con-
sider that when the membrane-damaged bacteria were
subjected to a continuous photocatalytic reaction, they
were finally broken by these ROSs, as shown in the
disappearance of the GFP gene-transformed E. coli on
the composite coatings during exposure to visible-light
illumination. We also deem that the greater surface rou-
ghness (Figure 1) offered by PTFE results in more air
pockets that provide additional oxygen for the pho-
tocatalytic reaction, which in turn leads to further ROS
generation to enhance the bactericidal activity of the
Cu/W 3-added PTFE particulate composite. O

Synergistic Antibacterial Performance of a Cu/WO3-Added PTFE Particulate Superhydrophobic
Composite under Visible-Light Exposure
426
(a) (b)
Figure 2. Bactericidal effects of PTFE particulate composite hydrophobic films, without (control) and with the addition of
Cu/WO3 (CW), on (a) E. co li; (b) Staphylococcus aureus and methicillin-resistant Staphylococcus aureus (MRSA), under visi-
ble-light illumination at 2000 lx for 24 h. The photo-bactericidal effect was significantly enhanced by combination of Cu/WO3
and PTFE, compared with the composite coating film having Cu/WO3 without PTFE.
A
B
Figure 3. Disappearance of green fluorescent protein (GFP) gene-transformed E. coli cells on 8 wt% Cu/WO3-added PTFE
particulate composite coating after 2000 lx of visible-light illumination for 24 h.
Figure 4 shows the key operational parameters which
affect the bactericidal activity of the composite materials.
By comparison of the bactericidal activity-value calcu-
lated using Equation (4), the activity of the newly deve-
loped hydrophobic composite material clearly depends
on the concentration of Cu/WO3 and visible-light in-
tensity. No bactericidal activities were observed in the
control samples (PTFE without Cu/WO3). It is reasona-
ble to believe that the Cu/WO3 nanoparticles are unique
materials which contribute to the bactericidal action of
the composite material. Furthermore, even with a very
low intensity of illumination (100 lx), the antimicrobial
value reached 1.7, signifying the decrease in the number
of viable E. coli cells nearly by two points on a logari-
thmic scale. Thus, we believe that this novel water-re-
pellent composite material may find application in such
places in hospitals and senior citizens’ homes.
material is contaminated with oil pollutants, its hydro-
phobicity will be reduced. It is generally considered that
this is because of the interaction that occurs between the
water molecule dipole moment and the dipole moment of
the carboxyl group (COOH) of oleic acid. Therefore, the
photocatalytic degradation of the PTFE particulate com-
posite is expected to be ameliorated by adding Cu/WO3.
Figure 5 shows that the Cu/WO3-added PTFE particulate
composite coating exhibited a self-cleaning performance
to oxidatively degrade oleic acid under visible light.
From the data, large decreases in the contact angles could
be observed in the composite coating with 3% Cu/WO3
when it was contaminated with oleic acid. After being
subjected to 1 mW·cm−2 of UV irradiation for 333 h, the
oleic acid was removed successfully only on the surface
of the Cu/WO3-added PTFE particulate composite coat-
ing, after which the contact angle recovered to its initial
value.
3.3. Self-cleaning Property Photocatalytic degradation of oleic acid has been re-
ported in several studies. In 2006, W. Dai, et al. reported
that the hydroxyl radicals produced by reaction of the
photogenerated holes with surface hydroxyl groups is the
main oxidant for the photocatalytic degradation of car-
3.3.1. Photocatalytic Degradation of the Cu/WO3-
Added PTFE Particulate Composite Coating on
Oleic Acid
It is well known that when a conventional water-repellent

Synergistic Antibacterial Performance of a Cu/WO3-Added PTFE Particulate Superhydrophobic
Composite under Visible-Light Exposure
427
Figure 4. Value of antibacterial activity evaluated on the
surface of the Cu/WO3-added PTFE particulate composite
film and the PTFE particulate composite film without Cu/
WO3 (controls), on E. coli under visible-light illuminetion at
various intensities for 24 h.
Figure 5. Recovering of the water contact angles of 3 wt%
Cu/WO3-added PTFE particulate composite coating con-
taminated with 0.5 vol% oleic acid diluted in n-heptane
during exposure to 1 mW·cm−2 of UV-A light for 333 h. ●:
Oleic acid (+), ○: Oleic acid (–). (a) Water droplet on 3 wt%
Cu−WO3-added PTFE particulate composite surface with-
out oleic acid contamination and UV-A illumination; (b)
Water droplet on 3 wt% Cu/WO3-added PTFE particulate
composite surface after contamination with oleic acid and
without UV-A illumination.
boxylic acids at the liquid-solid interface of TiO2 cata-
lysts [28]. In 2011 J. Rathousky and coworkers proposed
that the oxidative degradation of the TiO2 film was in-
duced by an attack of the hydroxyl radical on the double
bond. The eliminated hydroxyl radical could act cataly-
tically and thus cause accelerated degradation of unsatu-
rated compounds including fatty acids, which could be
expected to be proportional to the degree of its degrada-
tion, i.e., its transformation into more hydrophilic com-
pounds as well as into gaseous products (CO2 and H2O)
[29]. These published results and our findings confirm
that, although superhydrophobicity is not sufficient to
repel organic matter, especially oil, the photocatalytic oxi-
dization could eliminate these organic stains and preserve
the superhydrophobic surface after it had been exposed
to outdoor conditions for a long period of time.
It is noteworthy that neither the 8 wt% nor the 12 wt%
Cu/WO3-added PTFE particulate composite coatings
changed their contact angles even when they were conta-
minated with oleic acid. This observation was the same
in the 3 wt% sample (data not shown). We considered in
this case that the relatively high inclusion level of Cu/
WO3 greatly increased the surface energy of the fluori-
nated binder. This allows the oleic acid to seep through
the PTFE particles possessing low surface energy and to
adsorb the binder, allowing the superhydrophobicity to
still be maintained. These results indicate that the rela-
tively high level inclusion of Cu/WO3, a novel visible-
light-sensitive photocatalyst, into the PTFE particulate
composite improved the durability of its hydrophobicity.
3.3.2. Decomposition Performance of the Cu/WO3-
Added PTFE Particulate Composite Coating on
Gaseous Acetaldehyde
When a novel composite material is designed for indoor
use, an additional property expected is the air deo-
dorizing ability. We investigated this capability through
the photocatalytic degradation of gaseous acetaldehyde
(CH3CHO) using the Cu/WO3-added PTFE particulate
composite coating, as described earlier. The reaction time
profiles, shown in Figures 6(a) and (b), indicate the de-
crease in acetaldehyde concentration on the Cu/WO3-
added PTFE particulate composite coating under UV-A
(a) or UV-A plus visible light (b), while the simul-
taneous formation of CO2 is observed. The decomposi-
tion rate constant for gaseous acetaldehyde was cal-
culated to be in the range of approximately 0 - 0.3 h. We
can see from the data that the degradation rate under
UV-A plus visible-light illumination (k1 = 0.041) was
four times that under UV-A only (k1 = 0.010). Although
the degradation rates shown here were relatively low, the
novel composite material applied to a lag area as paint
could compensate for this shortcoming. In addition, the
increase in CO2 levels observed in conjunction with a
decline in gaseous acetaldehyde indicates the complete
oxidation of acetaldehyde. This is very important from
the viewpoint of practical applications, because acetal-
dehyde is known to be one of the principal odor-inducing
gases indoors, particularly in cigarette smoke [30,31].

Synergistic Antibacterial Performance of a Cu/WO3-Added PTFE Particulate Superhydrophobic
Composite under Visible-Light Exposure
428
Figure 6. Time profiles of the photocatalytic decomposition
of CH3CHO using 12 wt% Cu/WO3-added PTFE particu-
late hydrophobic composite material. (a) Illuminated with 1
mW·cm−2 of UV-A only; (b) Illuminated with 1 mW·cm−2 of
UV-A plus 2000 lx of visible-light.
4. Conclusion
In this paper, we have developed a novel water-repellent
composite material with photocatalytic activity, as shown
in antimicrobial and photocatalytic degradation perfor-
mance. This material is composed of a Cu/WO3 photo-
catalyst (a visible-light-sensitive photocatalyst), PTFE
particles, a fluorinated binder, and fluoro-oil. The com-
posite material exhibited a water contact angle greater
than 150˚, and a surface energy as low as 6 mN/m,
indicating superhydrophobicity or water repellency. The
novel water-repellent material completely inactivated E.
coli, S. aureus, and MRSA from ca. 2 – 4 × 105 CFUs
during 2000 lx of visible-light illumination for 24 h. In
particular, the extremely high inactivation of MRSA
showed that the developed superhydrophobic composite
material may be resistant to hospital-acquired infections.
Even at very low intensity, the visible-light induced
photocatalytic inactivation reduced E. coli cells by nearly
2 logs. The synergistic effect of the photocatalytic per-
formance and the hydrophobicity of the Cu/O3-added
PTFE particulate composite coating results in the signi-
ficant enhancement of bactericidal rate compared with
Cu/WO3 without PTFE particles composite coating. This
was attributed to the surface roughness provided by the
PTFE; more air pockets offered additional oxygen to the
photocatalytic reaction leading to greater reactive oxygen
species’ generation. We also clarified that organic stains
adsorbed on the composite surface could be successfully
removed utilizing UV-induced photocatalytic oxidation,
which resulted in sustainable high hydrophobic states.
Furthermore, the novel composite material photocata-
lytically decomposed gaseous acetaldehyde during UV-A
or UV-A irradiation plus visible light, while CO2 was
observed. These results suggest potential applications for
the Cu/WO3-added PTFE particulate hydrophobic com-
posite material both indoors for antibacterial action and
air deodorizing, and outdoors for prevention of con-
tamination.
5. Acknowledgements
This work was supported by Seeds Development Grant
08-201 from the Japan Science and Technology Agency.
The Cu/WO3 was supplied by Showa Titanium Co. Ltd
(Toyama, Japan), a member of the NEDO Project: “Pho-
tocatalytic industry emerging project in pursuit of a en-
vironmental society”. The authors gratefully acknow-
ledge the help of Konosuke Ikeda and Takashi Shimizu
of NTT Advanced Technology Corporation for sample
preparation. The authors also thank Dr. Sakai of the
Kanagawa Academy of Science and Technology for
useful discussions.
REFERENCES
[1] G. Yamauchi, H. Saito and K. Takai, “PTFE Based Water
Repellent Coating for Telecommunication Anten- nas,”
IEICE Transactions on Electronics, Vol. E83-C, No. 7,
2000, pp. 1139-1141.
[2] H. Saito, K. Takai, H. Takazawa and G. Yamauchi, “A
Study on Snow Sticking Weight to Water Repellent
Coating,” Materials Science Research International, Vol.
3, No. 4, 1997, pp. 216-219.
[3] C.-T. Hsieh, J.-M. Chen, R.-R. Kuo, T.-S. Lin and C.-F.
Wu, “Influence of Surface Roughness on Water- and
Oil-Repellent Surfaces Coated with Nanoparticles”, Ap-
plied Surface Science, Vol. 240, No. 1-4, 2005, pp. 318-
326. doi:10.1016/j.apsusc.2004.07.016
[4] Y. Yao, Y. Ohko, Y. Sekiguchi, A. Fujishima and Y. Ku-

Synergistic Antibacterial Performance of a Cu/WO3-Added PTFE Particulate Superhydrophobic
Composite under Visible-Light Exposure
429
bota, “Self-Sterilization Using Silicone Catheters Coated
with Ag and TiO2 Nanocomposite Thin Film,” Journal of
Biomedical Materials Research Part B: Applied Bioma-
terials, Vol. 85B, No. 2, 2008, pp. 453-460.
doi:10.1002/jbm.b.30965
[5] Y. Yao, T. Ochiai, H. Ishiguro, R. Nakano and Y. Kubota,
“Antibacterial Performance of a Novel Photocatalytic-
Coated Cordierite Foam for Use in Air Cleaners,” Applied
Catalysis B: Environmental, Vol. 106, No. 3-4, 2011, pp.
592-599. doi:10.1016/j.apcatb.2011.06.020
[6] P. S. M. Dunlop, C. P. Sheeran, J. A. Byrne, M. A. S.
McMahon, M. A. Boyle and K. G. McGuigan, “In-
activation of Clinically Relevant Pathogens by Pho-
tocatalytic Coatings,” Journal of Photochemistry and
Photobiology A: Chemistry, Vol. 216, No. 2-3, 2010, pp.
303-310. doi:10.1016/j.jphotochem.2010.07.004
[7] H. Irie, S. Washizuka, N. Yoshino and K. Hashimoto,
“Visible-Light Induced Hydrophilicity on Nitrogen-Sub-
stituted Titanium Dioxide Films,” Chemical Commu-
nications, Vol. 9, No. 11, 2003, pp. 1298-1299.
doi:10.1039/b302975a
[8] M. Kitano, K. Funatsu, M. Matsuoka, M. Ueshima and M.
Anpo, “Preparation of Nitrogen-Substituted TiO2 Thin
Film Photocatalysts by the Radio Frequency Magnetron
Sputtering Deposition Method and Their Photocatalytic
Reactivity under Visible Light Irradiation,” The Journal
of Physical Chemistry B, Vol. 110, No. 50, 2006, pp.
25266-25272. doi:10.1021/jp064893e
[9] H. E. Kamali, E. Marzbanrad, C. Zamani and B. Raissi,
“Nanocasting Synthesis of Ultrafine WO3 Nanoparticles
for Gas Sensing Applications,” Nanoscale Research
Letters, Vol. 5, No. 2, 2009, pp. 370-373.
doi:10.1007/s11671-009-9490-8
[10] G. Xi, B. Yue, J. Cao and J. Ye, “Fe3O4 Hierachical
Core-Shell Structure: High-Performance and Recyclable
Visible-Light Photocatalysis,” Chemistry—A European
Journal, Vol. 17, No. 18, 2011, pp. 5145-5154.
doi:10.1002/chem.201002229
[11] M. Ashokumar and P. Maruthamuthu, “Preparation and
Characterization of Doped WO3 Photocatalyst Powders,”
Journal of Materials Science, Vol. 24, No. 6, 1989, pp.
2135-2139. doi:10.1007/BF02385433
[12] H. Irie, S. Miura, K. Kamiya and K. Hashimoto,
“Efficient Visible Light-Sensitive Photocatalysts: Graf-
ting Cu(II) Ions onto TiO2 and WO3 Photocatalysts,”
Chemical Physics Letters, Vol. 457, No. 1-3, 2008, pp.
202-205. doi:10.1016/j.cplett.2008.04.006
[13] Y. Kitazaki and T. Hata, The Adhesion Society of Japan,
Vol. 8, No. 3, 1972, pp. 131-137.
[14] JIS R 1702, “Fine Ceramics (Advanced Ceramics, Ad-
vanced Technical Ceramics)—Test Method for Antibac-
terial Activity of Photocatalytic Products under Photo
Irradiation and Efficacy,” 2006.
[15] JIS R 1703-1, “Fine Ceramics (Advanced Ceramics, Ad-
vanced Technical Ceramics)—Test Method for Self-
Cleaning Performance of Photocatalytic Materials—Part
1: Measurement of Water Contact Angle,” 2007.
[16] JIS R 1701-2, “Fine Ceramics (Advanced Ceramics, Ad-
vanced Technical Ceramics)—Test Method for Air Pu-
rification Performance of Photocatalytic Materials—Part
2: Removal of Acetaldehyde,” 2008.
[17] G. Yamauchi, J. D. Miller, H. Saito, K. Takai, H. Taka-
zawa and T. Ueda, “The Wetting Characteristics of PTFE
Particulate Composites,” Materials Transactions, Vol. 37,
No. 4, 1996, pp. 721-728.
[18] J. D. Miller, S. Veeramasuneni, J. Drelich, M. R. Yala-
manchili and G. Yamauchi, “Effect of Roughness as
Determined by Atomic Force Microscopy on the Wetting
Properties of PTFE Thin Films,” Polymer Engineering &
Science, Vol. 36, No. 14, 1996, pp. 1849-1855.
doi:10.1002/pen.10580
[19] R. N. Wenzel, “Resistance of Solid Surfaces to Wetting
by Water,” Industrial & Engineering Chemistry Research,
Vol. 28, No. 8, 1936, pp. 988-994.
doi:10.1021/ie50320a024
[20] A. B. D. Cassie, “Contact Angle,” Discussions of the
Faraday Society, Vol. 3, 1948, pp. 11-16.
doi:10.1039/df9480300011
[21] A. Nakajima, K. Hashimoto, T. Watanabe, K. Takai, G.
Yamauchi and A. Fujishima, “Transparent Superhydro-
phobic Thin Films with Self-Cleaning Properties,” Lang-
muir, Vol. 16, No. 17, 2000, pp. 7044-7047.
doi:10.1021/la000155k
[22] T. Nishino, M. Meguro, K. Nakamae, M. Matsushita and
Y. Ueda, “The Lowest Surface Free Energy Based on
−CF3 Alignment,” Langmuir, Vol. 15, No. 13, 1999, pp.
4321-4323. doi:10.1021/la981727s
[23] J. D. Edgeworth, D. F. Treacher and S. T. Eykyn, “A
25-Year Study of Nosocomial Bacteremia in an Adult
Intensive Care Unit,” Critical Care Medicine, Vol. 27,
No. 8, 1999, pp. 1648-1650.
doi:10.1097/00003246-199908000-00002
[24] S. M. Smith, R. H. K. Eng, P. Bate, P. Fan-Havard and F.
Tecson-Tumang, “Mechanisms of Antimicrobial Resis-
tance and Implications for Epidemiology,” Journal of
Antimicrobial Chemotherapy, Vol. 26, No. 4, 1990, pp.
567-572. doi:10.1093/jac/26.4.567
[25] G. Gogniat, M. Thyssen, M. Denis, C. Pulgarin and S.
Dukan, “The Bactericidal Effect of TiO2 Photocatalysis
Involves Adsorption onto Catalyst and the Loss of
Membrane Integrity,” FEMS Microbiology Letters, Vol.
258, No. 1, 2006, pp. 18-24.
doi:10.1111/j.1574-6968.2006.00190.x
[26] P.-C. Maness, S. Smolinski, D. M. Blake, Z. Huang, E. J.
Wolfrum and W. A. Jacoby, “Bactericidal Activity of
Photocatalytic TiO2 Reaction: Toward an Understanding
of Its Killing Mechanism,” Applied and Environmental
Microbiology, Vol. 65, No. 9, 1999, pp. 4094-4098.
[27] W. A. Jacoby, P.-C. Maness, E. J. Wolfrum, D. M. Blake
and J. A. Fennell, “Mineralization of Bacterial Cell Mass
on a Photocatalytic Surface in Air,” Environmental Sci-
ence & Technology, Vol. 32, No. 17, 1998, pp. 2650-
2653. doi:10.1021/es980036f
[28] W. Dai, X. Wang, P. Liu, Y. Xu, G. Li and X. Fu,
“Effects of Electron Transfer between TiO2 Films and
Conducting Substrates on the Photocatalytic Oxidation of

Synergistic Antibacterial Performance of a Cu/WO3-Added PTFE Particulate Superhydrophobic
Composite under Visible-Light Exposure
430
Organic Pollutants,” The Journal of Physical Chemistry B,
Vol. 110, No. 48, 2006, pp. 13470-13476.
doi:10.1021/jp061483h
[29] J. Rathousky, V. Kalousek, M. Kolar, J. Jirkovsky and P.
Bartakb, Catalysis Toda, Vol. 161, 2011, pp. 202-208.
[30] G. Leonardos, D. Kendall and N. Barnard, “Odor Th-
reshold Determinations of 53 Odorant Chemicals,” Jour-
nal of the Air Pollution Control Association, Vol. 19, No.
2, 1969, pp. 91-95.
doi:10.1080/00022470.1969.10466465
[31] J. E. Amoore and E. Hautala, “Odor as an Aid to
Chemical Safety: Odor Thresholds Compared with Th-
reshold Limit Values and Volatilities for 214 Industrial
Chemicals in Air and Water Dilution,” Journal of Applied
Toxicology, Vol. 3, No. 6, 1983, pp. 272-290.
doi:10.1002/jat.2550030603