Photocatalytic activity of dispersed TiO2 particles deposited on glass fibers

Article abstract of DOI:10.1016/j.molcata.2005.11.007

Anatase TiO₂ particles were uniformly and dispersedly deposited on the surface of glass fibers by a liquid phase deposition (LPD) method from a TiF₄ aqueous solution upon addition of H₃BO₃ at 60 °C and then calcined at 60, 300 and 500 °C. The photocatalytic activity of the samples was evaluated by the photocatalytic oxidation of nitrogen monoxide (NO) in the gaseous phase. It was found that calcination temperatures obviously influenced the surface morphology and photocatalytic activity of the TiO₂ particles deposited on the glass fibers. At 300 °C, the TiO₂ samples exhibited the highest photocatalytic activity for the photocatalytic oxidation of NO and for the further conversion of NO₂ (from NO₂ to HNO₃) due to the enhancement of crystallization of anatase TiO₂ particles. At 500 °C, the photocatalytic activity of the sample decreased significantly due to the dropping of many TiO₂ particles from the glass fibers. Compared with the TiO₂ film photocatalyst, the TiO₂ particles deposited on the glass fibers exhibited a lower deactivation rate.

Full text of DOI:10.1016/j.molcata.2005.11.007

Journal of Molecular Catalysis A: Chemical 246 (2006) 206–211
Photocatalytic activity of dispersed TiO2 particles deposited on glass fibers
Huogen Yua,b, S.C. Leea,∗, Jiaguo Yub,∗, C.H. Aoa
a Department of Civil and Structural Engineering, Research Center for Environmental Technology and Management,
The Hong Kong Polytechnic University, Hung Horn, Kowloon, PR China
b State Key Laboratory of Advanced Technology for Material Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, PR China
Received 28 September 2005; received in revised form 29 September 2005; accepted 7 November 2005
Available online 9 December 2005
Abstract
Anatase TiO2 particles were uniformly and dispersedly deposited on the surface of glass fibers by a liquid phase deposition (LPD) method from
a TiF4 aqueous solution upon addition of H3BO3 at 60 ◦C and then calcined at 60, 300 and 500 ◦C. The photocatalytic activity of the samples was
evaluated by the photocatalytic oxidation of nitrogen monoxide (NO) in the gaseous phase. It was found that calcination temperatures obviously
influenced the surface morphology and photocatalytic activity of the TiO2 particles deposited on the glass fibers. At 300 ◦C, the TiO2 samples
exhibited the highest photocatalytic activity for the photocatalytic oxidation of NO and for the further conversion of NO2 (from NO2 to HNO3)
due to the enhancement of crystallization of anatase TiO2 particles. At 500 ◦C, the photocatalytic activity of the sample decreased significantly due
to the dropping of many TiO2 particles from the glass fibers. Compared with the TiO2 film photocatalyst, the TiO2 particles deposited on the glass
fibers exhibited a lower deactivation rate.
© 2005 Elsevier B.V. All rights reserved.
Keywords: TiO2 particles; Photocatalytic activity; Glass fibers; LPD; Deactivation rate; Nitrogen monoxide
1. Introduction
concentration can cause headache, fatigue, dizziness, difficult
breaking, throat spasms and fluid build-up in the lungs. Studies
have indicated that NO concentration is usually in the range
70–500 ppb in the indoor environment [6,7]. Owing to its low
concentration, it is not suitable and effective to use traditional
remediation technique such as adsorption and filtration to
reduce or eliminate the pollutants [8,9]. Moreover, the use of
adsorbents merely transfers pollutants from the gaseous phase to
the solid phase and easily causes post-disposal and regeneration
problems. Despite the importance of IAQ, only few studies
have reported on the feasibility of applying photocatalytic
technology for the removal of indoor air pollutants [2,3].
There is an increasing concern about the indoor air quality
(IAQ) because the quality of indoor air has a direct impact on
human healthy due to the lengthened inhabitation in the indoor
environment [1–3]. Modern buildings have been designed
to be more airtight in order to decrease the consumption of
energy since energy conservation measures were instituted in
office buildings in the 1970s due to energy crisis. However, the
decrease of the intake of fresh air resulted in the build-up of
various indoor air pollutants. Indoor domestic appliances, such
as gas stoves and heaters, could be the main sources of pollutants
due to the burning of coal, oil and natural gas, particularly in the
areas that are poorly ventilated [4]. Moreover, a great number
of materials used in construction, furnishing and insulation
further increased the amount of pollutants [5]. Among various
pollutants, nitrogen oxides are the most common pollutants
found in the indoor environment [3]. It is well known that
the lengthened exposure to the nitrogen oxides with a high
Photocatalysis technique provides a very promising solu-
tion for the removal of indoor air pollutants and TiO2 is one
of the most effective photocatalysts due to its strong oxidiz-
ing power, non-toxicity and long-term photostability [10–20].
When TiO2 powder is used as a photocatalyst for water purifi-
cation, it shows high photocatalytic activity due to its large
surface area. However, conventional powdered photocatalysts
have a serious limitation—the need for post-treatment separa-
tion in a slurry system after photocatalytic reaction. Meanwhile,
mobile photocatalyst powder is also not applicable for air purifi-
∗
Corresponding authors.
E-mail addresses: ceslee@polyu.edu.hk (S.C. Lee), jiaguoyu@yahoo.com
(J. Yu).
1381-1169/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2005.11.007

H. Yu et al. / Journal of Molecular Catalysis A: Chemical 246 (2006) 206–211
207
cation, as it may contribute to respirable particles that cause
adverse human health problems. Though this can be overcome
by immobilizing TiO2 particles as thin films on solid substrates
[21–25], the formation of TiO2 films on the substrates signifi-
cantly reduced the specific surface area of TiO2 photocatalysts,
resulting in a decrease of photocatalytic activity. If anatase TiO2
particles can be uniformly and dispersedly deposited on the
surface of fibers, the prepared TiO2 photocatalysts not only
have a large surface area and keep high photocatalytic activity,
but also can avoid the disadvantages of TiO2 powdered pho-
tocatalysts. Therefore, it is very interesting to investigate the
photocatalytic activity of the TiO2 particles deposited on the
fibers.
In the present work, anatase TiO2 particles were uniformly
anddispersedlydepositedonthesurfaceoftheglassfibersfroma
TiF4 aqueous solution upon addition of H3BO3 at 60 ◦C and then
calcined at 60, 300 and 500 ◦C. The as-prepared TiO2 samples
were characterized with X-ray diffraction (XRD) and scanning
electron microscopy (SEM). The photocatalytic activity of the
samples was evaluated by the photocatalytic oxidation of nitro-
gen monoxide (NO) in the gaseous phase.
photocatalytic oxidation of NO, which was fed into a laboratory-
scale continuous flow photoreactor. The inlet concentration of
NO was 200 ppb. The detailed experimental set-up and process
have been reported elsewhere [26]. A reactor with a volume of
18.6 L (20.1 H × 44.2 L × 21 W cm) and its surface coated with
a teflon film (BYTAC Type AF-21) was used for this study. A
6 W 365 nm UV lamp (Cole-Parmer Instrument Co., USA) was
used as light source and its intensity was determined with a UV
meter (Spectroline DRC-100X). The UV lamp was horizontally
placed at the upper part of the reactor, 14 cm from both ends.
The UV intensity measured in all experiments was 600 ␮W/cm2.
The TiO2 sample was supported by a teflon film and fixed hori-
zontally at a vertical distance of 5 cm away from the UV lamp.
Stainless steel sampling ports and teflon tubing were used to
connect the reactor and the analytical instruments. A zero air
generator (Thermo Environmental Inc., Model 111) was used
to supply the air stream. The desired humidity of the flow was
controlled by passing a zero air stream through a humidifica-
tion chamber. The reactant stream and the zero air streams were
pre-mixed in a gas blender (Advanced Pollution Instrumenta-
tion Inc., Model 700) and a mass flow controller controlled
the desired flow. After the inlet and the outlet concentration
of the target pollutants achieved equilibrium (30 min), the UV
lamp was turned on and initiated the reaction. The concentra-
tion of NO was continuously measured by a Chemiluminescence
NO analyzer (Thermo Environmental Instruments Inc., Model
42c), which monitored NO, NO2 and NOx (NOx represents
NO + NO2) with a sampling rate of 0.7 L/min. The photocat-
alytic activity of TiO2 particle photocatalyst was characterized
by the removal rates of NO, NO2 and NOx. The NO, NO2 and
NOx removal rates (%) are calculated according to the following
equations [2,3]:
2. Experimental
2.1. Preparation
TiF4 and H3BO3 were dissolved in distillated water in
order to prepare the respective precursor solutions. The as-
prepared aqueous solutions of TiF4 and H3BO3 were mixed,
stirred and used as a deposition solution. The initial concen-
trations of the deposition solution were 0.025 M TiF4 and
0.075 M H3BO3. The pH value of the deposition solution
was adjusted to ca. 2.0 using hydrochloric acid (1 M HCl) or
aqueous ammonia (1 M NH4OH). Then the glass fiber clothes
(0.1 H × 20.0 L × 20.0 W cm) were immersed and suspended in
a 250 ml deposition solution at 60 ◦C for 12 h. After the TiO2-
coated glass fibers were taken out and rinsed with distilled water,
the samples were dried at 60 ◦C for 2 h and then calcined at 300
and 500 ◦C in air for 2 h, respectively. Apart from the above-
described TiO2 particle samples, TiO2 film deposited on the
stainless steel was also prepared under the same experimental
conditions.
[NO]inlet − [NO]outlet
NO removal (%) =
NO2 removal (%) =
NOx removal (%) =
× 100%
(1)
(2)
(3)
[NO]inlet
[NO2]inlet − [NO2]outlet
× 100%
× 100%
[NO]inlet
[NOx]inlet − [NOx]outlet
[NO]inlet
where [NO]inlet, [NO2]inlet and [NOx]inlet represent the inlet pol-
lutant concentrations and [NO]outlet, [NO2]outlet and [NOx]outlet
are the outlet concentrations measured at an irradiation time of
120 min after the UV lamp was turned on.
2.2. Characterization
X-ray diffraction (XRD) patterns were obtained on a Philips
MPD 18801 X-ray diffractometer using Cu K␣ irradiation at a
scan rate of 0.05◦ 2θ S−1 and were used to determine the crys-
talline phase and the crystallite size. The accelerating voltage
and the applied current are 35 kV and 20 mA, respectively. The
scanning electron micrographs (SEM) were obtained on a Leica
Stereoscan 440 microscope.
3. Results and discussion
3.1. Surface morphologies and crystalline phase
The glass fibers used as the substrates show a wide diam-
eter distribution range from 100 nm to 2 ␮m. When the glass
fibers were immersed into the deposition solution, TiO2 parti-
cles were gradually deposited on their surface. The formation
process of the TiO2 particles on the glass fibers was reported
in our previous study [26]. When the TiO2-coated glass fibers
were heat-treated at 300 ◦C, the morphology of the TiO2 parti-
cles on the glass fibers has no obvious change. Fig. 1(a) and (b)
2.3. Photocatalytic activity
The evaluation of photocatalytic activity of the TiO2 particle
photocatalyst was performed in the gas phase by measuring the

208
H. Yu et al. / Journal of Molecular Catalysis A: Chemical 246 (2006) 206–211
Fig. 1. SEM photographs of the TiO2 particles deposited on the glass fibers and calcined at 300 ◦C ((a) and (b)) and 500 ◦C ((c) and (d)).
show the SEM images of the surface of the TiO2-coated glass
fibers calcined at 300 ◦C. It can be found that the TiO2 parti-
cles with sizes of 200–400 nm are uniformly and dispersedly
deposited on the surface of the glass fibers. Further, observation
indicates that the TiO2 particles deposited on the glass fibers
are composed of many smaller TiO2 particles with a size of
20–70 nm (as shown in Fig. 1(b)). At 500 ◦C, the number of
the TiO2 particles deposited on the glass fibers decrease signifi-
cantly (as shown in Fig. 1(c) and (d)). This may be attributed to
the difference in thermal expansion coefficients between TiO2
and glass fibers, which causes the interfacial stresses and results
in the dropping of TiO2 particles from the surface of the glass
fibers.
The intensities of X-ray diffraction peaks of the TiO2 parti-
cle photocatalysts deposited on the glass fibers were very weak
for phase analysis due to the limited amount of TiO2 particles.
To determine the crystalline phase and crystallite size of the
TiO2 particles deposited on the glass fibers, TiO2 powders were
also prepared from the same deposition solution without the
addition of the glass fibers. Fig. 2 shows the XRD patterns
of the TiO2 powder samples calcined at 60, 300 and 500 ◦C.
At 60 ◦C, only the diffraction peaks of anatase are observed.
This indicates that crystalline anatase TiO2 particles could be
prepared at 60 ◦C. The average crystallite size of the TiO2 pow-
ders was calculated according to Scherrer’s equation from the
(1 0 1) diffraction peak of anatase and was ca. 6 nm at 60 ◦C.
With increasing calcination temperatures, the peak intensities
of anatase increase and the width of the (1 0 1) peak becomes
narrow, which is ascribed to the growth of anatase crystallites
and the enhancement of crystallization. The average crystal-
lite sizes of the TiO2 powders calcined at 300 and 500 ◦C are
ca. 10 and 15 nm, respectively. Therefore, it can be concluded
that the TiO2 particles deposited on the surface of the glass
fibers (as shown in Fig. 1) consist of many smaller anatase TiO2
crystallites.
3.2. Effect of calcination temperature on the photocatalytic
activity
Fig. 3 shows the photocatalytic activity of the as-prepared
TiO2 particles deposited on the glass fibers at 60 ◦C for the pho-
tocatalytic oxidation of 200 ppb NO. It can be seen that prior
to UV illumination, the adsorption and desorption of NO have
reached an equilibrium. When UV lamp was turned on, the
photocatalytic oxidation of NO was initiated immediately. The
concentration of NO dropped rapidly in the first 20 min and then
reached a lowest value of ca. 63 ppb. After that, the concentra-
tion of NO increased slightly with increasing irradiation time.
This was ascribed to the accumulation of HNO3 on the surface
of TiO2 particles, resulting in the deactivation of TiO2 photocat-
alyst [27]. After UV irradiation for 120 min, the concentration
of NO gradually reached a photo-steady-state concentration (ca.
Fig. 2. XRD patterns of the TiO2 powders calcined at 60 ◦C (a), 300 ◦C (b) and
500 ◦C (c).

H. Yu et al. / Journal of Molecular Catalysis A: Chemical 246 (2006) 206–211
209
health. Therefore, it is not enough to evaluate the photocatalytic
activity of TiO2 samples only by the removal rate of NO. More
attention should be paid to the further conversion of NO2 (from
NO2 to HNO3), because HNO3 is more easily removed in prac-
tice. During the photocatalytic oxidation of NO, NO2 is the
intermediate and can further react with OH• to form HNO3 (Eq.
(5)). To evaluate the further conversion from NO2 to HNO3, the
conversion rate of NO2was defined as follows:
[NO]inlet − [NOx]outlet
NO2 conversion (%) =
× 100% (6)
[NO]inlet − [NO]outlet
where [NO]outlet and [NOx]outlet were the outlet concentrations
measured at an irradiation time of 120 min after the UV lamp
was turned on. The conversion rates of NO2 are shown in Table 1.
It can be seen that the NO2 conversion rate is over 50% when
calcination temperature is not higher than 300 ◦C. At 500 ◦C,
however, it decreases significantly due to the less TiO2 photo-
catalysts on the surface of the glass fibers. Therefore, to obtain
the TiO2-coated glass fibers with highly photocatalytic activity,
the clacination temperature should be kept at or below 300 ◦C.
Fig. 3. Photocatalytic activity of the as-prepared TiO2 particles deposited on the
glass fibers at 60 ◦C for the photocatalytic oxidation of 200 ppb NO. Residence
time: 11.4 min; humidity levels: 2100 ppmv.
88 ppb). However, the concentration of the generated NO2 by the
photocatalytic oxidation of NO almost kept a constant.
To evaluate the effect of calcination temperatures on the pho-
tocatalyticactivityofTiO2 particlesdepositedontheglassfibers,
the prepared samples were then calcined at 300 and 500 ◦C for
2 h, respectively. When calcination temperature was higher than
500 ◦C, the fiber was easily destroyed due to its low melting
point. Therefore, themaximumcalcinationtemperaturewaslim-
ited to 500 ◦C. Table 1 lists the photocatalytic activities of the
TiO2 particles deposited on the glass fibers and calcined at 60,
300 and 500 ◦C. It can be observed that the removal rate of NO
increases with increasing calcination temperatures. At 300 ◦C,
the TiO2 particle sample shows the highest photocatalytic activ-
ity. This is ascribed to the enhancement of crystallization of
anatase TiO2 particles (see Fig. 2). At 500 ◦C, the removal rate
of NO obviously decreases from 64.87% (at 300 ◦C) to 19.35%.
This is due to the dropping of a large number of TiO2 particles
from the surface of the glass fibers (as shown in Fig. 1(c) and
(d)).
3.3. Effect of irradiation time and reaction cycles on the
photocatalytic activity
It is important for a photocatalyst to have a long-term and
repeated photocatalytic activity, which can reduce the times of
photocatalyst replacement. Fig. 4 shows the effect of irradiation
time on photocatalytic activity of the TiO2 particles deposited
on the glass fibers at 60 ◦C for the photocatalytic oxidation
of 200 ppb NO. It can be seen that the concentration of NO
slightly increases with increasing UV irradiation time. This indi-
cates that the TiO2 particles deposited on the glass fibers had a
low deactivation rate even for 12 h UV irradiation. However,
no deactivation was found in our previous study for the photo-
catalytic degradation of BETX (benzene, toluene, ethybenzene
and o-xylene) [3]. The difference in the deactivation rate may be
attributed to different pollutant concentrations and the amount of
For the photocatalytic oxidation of NO, the following reac-
tions may exist [28,29].
•
NO + HO2 → NO2 + OH•
(4)
(5)
NO2 + OH• → HNO3
It is well known that nitrogen oxides (NO and NO2) are a
major pollution source in our environment and harmful to human
Table 1
Effects of calcination temperatures on the photocatalytic activity of the TiO2
particles deposited on the glass fibers
Temperature
(◦C)
NO removal
(%)
NO2 removal
(%)
NOx removal
(%)
NO2
conversion
(%)
60
300
500
55.5
64.9
19.4
−24.9
−29.6
−17.8
30.6
35.2
1.6
55.2
54.3
8.2
Fig. 4. Effect of irradiation time on photocatalytic activity of the TiO2 particles
deposited on the glass fibers at 60 ◦C for the photocatalytic oxidation of 200 ppb
NO. Residence time: 11.4 min; humidity level: 2100 ppmv.

210
H. Yu et al. / Journal of Molecular Catalysis A: Chemical 246 (2006) 206–211
ically oxidized into NO2 and then further oxidized into HNO3.
The formed HNO3 would be probably adsorbed to the active
sites of TiO2 photocatalyst and led to the decrease of photo-
catalytic activity of TiO2 particles. In this study, however, it
was found that the photocatalytic activity of the TiO2 particles
deposited on the glass fibers was not obviously affected by the
previous photocatalytic reactions. Therefore, it was reasonable
to suggest that the HNO3 adsorbed on the active sites could
transfer to non-active sites of TiO2 particles or the surface of the
glass fibers and then recovered to a surface similar to the virgin
TiO2 before UV irradiation. Another possible reason was that
the NO2 intermediate might accumulate on the active sites of
TiO2 particles and let the TiO2 photocatalyst deactivate. When
UV lamp was turn off, the NO2 molecules could transfer into the
air steam due to the competitive adsorption of NO molecules,
leading to the recovery of active sites on the surface of TiO2
particle photocatalyst.
Fig. 5. Effect of reaction cycles on photocatalytic activity of the TiO2 particles
deposited on the glass fibers at 60 ◦C for the photocatalytic oxidation of 200 ppb
NO. Residence time: 11.4 min; humidity level: 2100 ppmv.
3.4. Comparison of photocatalytic activity of TiO2 particles
and thin films
the TiO2 photocatalysts used. In our previous study, the BETX
concentration was kept at ca. 35 ppb and the weight of the TiO2
photocatalyst used was ca. 1.64 g. However, in this study, the
NO concentration was maintained at ca. 200 ppb and the weight
of the TiO2 photocatalyst employed was lower than 0.5 g cal-
culated according to the experimental conditions. Our previous
results suggested that a higher pollutant concentration and less
amount of TiO2 photocatalyst might cause an obvious deacti-
vation, while the deactivation was hardly observed when the
concentration pollutants was very low and more photocatalyst
was applied in a reaction system [2,3]. Other researchers also
reported a similar deactivation of catalyst when pollutant con-
centrations were high (several hundreds ppm) [30,31].
Fig. 5 shows the effect of reaction cycles on photocatalytic
activity of the TiO2 particles deposited on the glass fibers at
60 ◦C for the photocatalytic oxidation of 200 ppb NO. After
adsorption and desorption reached equilibrium, the UV light was
turned on for 1 h and then turned off for 30 min to recover to the
equilibrium status of adsorption and desorption. This process
was repeated for four times to evaluate the effect of reaction
cycles on the photocatalytic activity of the TiO2-coated glass
fibers. It was found that when the UV lamp was turned on,
NO concentration decreased rapidly and reached a lowest value.
Then, with increasing UV irradiation time, the NO concentra-
tion gradually increased from 66.0 ppb (A) to 81.3 ppb (B). This
could be ascribed to the decreasing number of the active sites
of TiO2 particles due to the formation of HNO3. However, it
should be noted that at the following reaction cycle, a similar
low NO concentration of 66.5 ppb (C) could also be obtained
at the beginning of UV irradiation and then the photocatalytic
oxidation of NO showed a similar process to the former pho-
togradation reaction (from A to B). It could be inferred that the
previous reaction cycles had no an obvious effect on the photo-
catalytic activity of the TiO2 particle samples. This phenomenon
was also observed in the further repeated photocatalytic oxida-
tion experiments of NO, as shown in the Fig. 5 (D and E). When
UV lamp was turned on, the NO molecules were photocatalyt-
To further evaluate the photocatalytic activity and the deac-
tivation rate of the TiO2 particles deposited on the glass fibers,
the TiO2 film was also prepared on the stainless steel substrate
under the same deposition conditions. Fig. 6 shows a typical
surface morphology of the as-prepared TiO2 film deposited on
the stainless steel and dried at 60 ◦C. The TiO2 film is com-
posed of many TiO2 particles with a size of 50–100 nm. Further,
observation indicates that the TiO2 particles are the aggregates
of many smaller TiO2 particles with a size of 20–50 nm, which
was similar to the image of the TiO2 particles deposited on the
glass fibers (as shown in Fig. 1). Fig. 7 shows the compari-
son of photocatalytic activity of the TiO2 particles deposited
on the glass fiber and TiO2 thin film on the stainless steel for
the photocatalytic oxidation of 200 ppb NO. Compared with the
TiO2 particles deposited on the glass fibers, the TiO2 film shows
a higher photocatalytic activity at the beginning of photocat-
alytic reaction. However, the photocatalytic activity of TiO2 film
decreases rapidly. After 70 min, the photocatalytic activity of the
TiO2 particles deposited on the glass fiber is higher than that of
Fig. 6. SEM image of the TiO2 film deposited on the stainless steel at 60 ◦C.

H. Yu et al. / Journal of Molecular Catalysis A: Chemical 246 (2006) 206–211
211
Acknowledgements
This work was partially supported by the National Natural
Science Foundation of China (50272049, 20473059). This work
was also financially supported by the Excellent Young Teachers
ProgramofMOEofChina, Project-SponsoredbySRFforROCS
of SEM of China and the Dean Reserve Fund from the Hong
Kong Polytechnic University.
References
[1] A.P. Jones, Atoms. Environ. 33 (1999) 4535.
[2] C.H. Ao, S.C. Lee, Appl. Catal. B44 (2003) 191.
[3] C.H. Ao, S.C. Lee, C.L. Mak, L.Y. Chan, Appl. Catal. B 42 (2003)
119.
[4] S.O. Baek, Y.S. Kim, R. Perry, Atoms. Environ. 31 (1997) 529.
[5] S.C. Lee, N.H. Kwok, H. Guo, W.T. Hung, Sci. Total Environ. 302
(2003) 75.
[6] S.C. Lee, L.Y. Chan, Environ. Int. 24 (1998) 729.
[7] C.J. Weschler, H.C. Shields, D.V. Naik, Environ. Sci. Technol. 28 (1994)
2120.
Fig. 7. Comparison of photocatalylic activity of the TiO2 particles deposited on
the glass fiber and TiO2 thin films on stainless steel for the photocatalytic oxida-
tion of 200 ppb NO. Deposition temperature: 60 ◦C; residence time: 11.4 min;
humidity level: 2100 ppmv.
[8] C.H. Ao, S.C. Lee, J.C. Yu, J. Photochem. Photobiol. A156 (2003) 171.
[9] F.I. Khan, A.K. Ghoshal, J. Loss Prev. Process Ind. 13 (2000) 527.
[10] K. Honda, A. Fujishima, Nature 238 (1972) 37.
[11] H. Tada, M. Yamamoto, S. Ito, Langmuir 15 (1999) 3699.
[12] J.G. Yu, M.H. Zhou, B. Cheng, H.G. Yu, X.J. Zhao, J. Mol. Catal. A
227 (2005) 75.
[13] J.G. Yu, H.G. Yu, B. Cheng, X.J. Zhao, J.C. Yu, W.K. Ho, J. Phys.
Chem. B 107 (2003) 13871.
[14] F.B. Li, X.Z. Li, Appl. Cata. A228 (2002) 15.
[15] J. Peral, D.F. Ollis, J. Catal. 136 (1992) 554.
[16] J.G. Yu, J.C. Yu, M.K.P. Leung, W.K. Ho, B. Cheng, X.J. Zhao, J.C.
Zhao, J. Catal. 217 (2003) 69.
[17] J.C. Yu, W.K. Ho, J. Lin, H. Yip, P.K. Wong, Environ. Sci. Technol. 37
(2003) 2296.
[18] X.Z. Li, F.B. Li, Environ. Sci. Technol. 35 (2001) 2381.
[19] J.C. Yu, J.G. Yu, W.K. Ho, Z.T. Jiang, L.Z. Zhang, Chem. Mater. 14
(2002) 3808.
TiO2 thin film on the stainless steel, indicating that the TiO2
particles deposited on the glass fiber exhibits a lower deactiva-
tion rate for the photocatalytic oxidation of NO. This further
confirms that the formed HNO3 from the photocatalytic oxida-
tion of NO can diffuse to the surface of glass fibers due to its
larger surface area. On the contrary, for the TiO2 film deposited
on the stainless steel, the photocatalytic reaction of NO occurs
on the surface of the film and no other space can be used for
the diffusion and transfer of HNO3. Therefore, the accumula-
tion of HNO3 on the surface of the TiO2 film leads to a higher
deactivation rate.
4. Conclusion
[20] H. Kishimoto, K. Takahama, N. Hashimoto, Y. Aoi, S. Deki, J. Mater.
Chem. 8 (1998) 2019.
Anatase TiO2 particles could be uniformly and dispersedly
deposited on the surface of the glass fibers by a LPD method
using TiF4 as the precursor at 60 ◦C. Calcination temperature
obviously influenced the surface morphology and photocatalytic
activity of the TiO2 particles deposited on the glass fibers. When
the calcination temperature was not higher than 300 ◦C, the TiO2
samples showed a high photocatalytic activity for the photocat-
alytic oxidation of NO and for the further conversion of NO2
(from NO2 to HNO3). In contrast, at 500 ◦C, the sample exhib-
ited a low photocatalytic activity due to the dropping of TiO2
particles from the glass fibers. Compared with the TiO2 film
photocatalyst, the TiO2 particle photocatalyst prepared by this
method could maintain a long-term and repeated photocatalytic
activity and a low deactivation rate.
[21] G. Balasubramanian, D.D. Dionysiou, M.T. Suidan, Y. Subramanian, I.
Baudin, J.M. Laine, J. Mater. Sci. 38 (2003) 823.
[22] H. Nagayama, H. Honda, H. Kawahara, J. Electrochem. Soc. 135 (1988)
2013.
[23] H. Pizem, C.N. Sukenik, U. Sampathkumaran, A.K. McIlwain, M.R. De
Guire, Chem. Mater. 14 (2002) 2476.
[24] Y. Masuda, S. Ieda, K. Koumoto, Langmuir 19 (2003) 4415.
[25] S. Deki, Y. Aoi, O. Hiroi, A. Kajinami, Chem. Lett. 6 (1996) 433.
[26] H.G. Yu, S.C. Lee, C.H. Ao, J.G. Yu, J. Cryst. Growth 280 (2005)
612.
[27] I. Ibusuki, K. Yakeuchi, J. Mol. Catal. 88 (1994) 93.
[28] Y. Komazaki, H. Shimizu, S. Tanaka, Atoms. Environ. 33 (1999)
4363.
[29] S. Matsuda, H. Hatano, A. Tsutsumi, Chem. Eng. J. 82 (2001) 183.
[30] O. Hennezel, D.F. Ollis, J. Catal. 167 (1997) 118.
[31] R.M. Alberici, W.F. Jardim, Appl. Catal. B 14 (1997) 55.