Carbon coating stabilized Ti3+-doped TiO2 for photocatalytic hydrogen generation under visible light irradiation

Article abstract of DOI:10.1039/c5dt01204j

Self-doping by Ti³⁺ is a useful method to expand the light response of TiO₂ into the visible light region. However, to obtain a stable Ti³⁺-doped TiO₂ seems to be a challenge due to the easy oxidation of Ti³⁺ during the heterogeneous reaction. Here, we propose a simple carbon coating route to stabilize the Ti³⁺-doped TiO₂, in which both the Ti³⁺ and precursor of the carbon coating layer were in situ formed from the hydrothermal hydrolysis of titanium isopropoxide. The carbon coated Ti³⁺-doped TiO₂ exhibited excellent stability for photocatalytic hydrogen production. Based on electron paramagnetic resonance (EPR) analysis, the proposed stabilizing mechanism is that the conductive carbon coating layer as a barrier layer prevents the H₂O and O₂ from diffusing into the surface of the photocatalyst, which can oxidize the surface O vacancies and Ti³⁺ in TiO₂. Our findings offer a simple route to prepare a highly stable TiO₂-based photocatalyst with visible light response.

Full text of DOI:10.1039/c5dt01204j

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Article
3+
Carbon coating stabilized Ti -doped TiO for photocatalytic hydrogen generation
2
under visible light irradiation
a
a
b
a
,b,c,d
a,c,d
Gao Fu, Peng Zhou, Meiming Zhao, Weidong Zhu, Shicheng Yan* , Tao Yu*
Zou
and Zhigang
a,b,c,d
5
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
3
+
Abstract: Self doping by Ti is a useful way to expand the light response of TiO into visible light region. However, to obtain a stable
2
3+
3+
Ti ꢀdoped TiO seems a challenge due to the easy oxidation of Ti during the heterogeneous reaction. Here, we proposed a simple
carbon coating route to stabilize the Ti ꢀdoped TiO , in which both the Ti and precursor of carbon coating layer were in situ formed
2
from the hydrothermal hydrolysis of titanium isopropoxide. The carbon coated Ti ꢀdoped TiO exhibited the excellent stability for
2
3
+
3+
1
1
2
2
3
3
4
4
0
5
0
5
0
5
0
5
3+
2
photocatalytic hydrogen production. Based on electron paramagnetic resonance (EPR) analysis, a proposed stabilizing mechanism is that
the conductive carbon coating layer as a barrier layer prevents the H O and O from diffusing into the surface of the photocatalyst, which
2
2
3
+
can oxidize the surface O vacancies and Ti in TiO . Our findings offer a simple route to preparing the highly stable TiO ꢀbased
2
2
photocatalyst with visible light response.
3
+
1
. Introduction
Therefore, it seems a challenge to prepare the stable Ti ꢀdoped
TiO with anatase phase. Directly burning the carbonꢀcontaining
2
3
+
Since Fujishima discovered that TiO can act as a photoꢀ 50 Ti precursor in ethanol, the 200 h photostable Ti ꢀdoped TiO
2
2
1
electrochemical waterꢀsplitting catalyst in 1972, which was once
proposed as the most promising material for largeꢀscale hydrogen
production. However, the large band gap (3.2 eV for anatase and
with a mixture phase of anatase and rutile was prepared. However,
3
+
there was no explanation on the high stability of Ti in such
prepared TiO . Noting that the elemental analysis proved the
existence of the carbon in the sample, this probably means that
2
2
3
.0 eV for rutile) determined that the TiO only absorbed the
2
3
+
ultraviolet light which makes up 3.5% of the solar energy, 55 the surface carbon as a protective layer prevents Ti from
1
0
corresponding to a low solarꢀtoꢀhydrogen conversion efficiency
oxidizing by H
O and O . Indeed, it has been demonstrated that
2 2
2ꢀ5
of 1.8%. Enormous efforts, such as element doping, organic
compounds sensitizing and forming heterojunctions with narrowꢀ
bandꢀgap semiconductors were made for expanding light
the carbon coating can improve the stability of photocatalysts
such as CdS and MnO
transformation from anatase to rutile at high temperatures.
19
20
, and also can suppress the phase
x
2
1, 22
6
, 7
3+
absorption edge of TiO .
For element doping, selfꢀdoping of 60 These evidence indicated that the highly stable Ti ꢀdoped
2
3+
Ti into crystal lattice of TiO , which introduced an energy level
0.7ꢀ1.2eV) below the conduction band (CB) of TiO , could not
anatase TiO can be prepared by using the carbon coating method
2
to stabilize both the Ti and anatase phase.
2
3
3+
(
2
only red shift the absorption band edge, but also increase the
carries concentration. Therefore, Ti doping was considered to
Here, we used an in situ hydrolysis of titanium isopropoxide to
2
3+
3+
form carbonꢀcoated anatase TiO nanocrystals with Ti doping
2
3
+
be an effective and promising route for obtaining the visibleꢀ 65 into the crystal lattice. We found that both the bulk Ti and
8
, 9
3+
lightꢀresponse TiO ꢀbased photocatalysts.
surface oxygen vacancies were stable in the carbon coated Ti ꢀ
doped TiO photocatalyst during 12 h photocatalytic hydrogen
production. EPR analysis confirmed that the highly stable Ti in
carbon coated TiO resulted from the protective effect of surface
70 carbon coating layer. Our results provided a simple method to
2
3+
4+
Ti could be made from reduction of Ti or oxidization of
2
2+ 9
3+
3+
Ti . A general method to obtain the Ti ꢀdoped TiO is using
2
the reducers with strong reductive ability, such as 2ꢀ
2
1
0, 11
12
13
14, 15
4+
ethylimidazole
, N H , H2 and NaBH4
, to reduce Ti
2
4
3+
3+
to Ti by calcining or hydrothermal treatment. In these routes
obtain stable Ti ꢀdoped TiO
photocatalysis.
for applications in the field of
2
reported, the products usually were rutile TiO or a mixture of
2
rutile and anatase TiO due to the facile phase transformation
2
from anatase to rutile during the calcination. A few researches
Experimental details
3
+
have reported Ti
doped anatase TiO by a hydrolysisꢀ
75
A slightly improved hydrothermal way with subsequent
2
3
+
3+ 16ꢀ
3+
hydrothermal method, using Ti salts as the source of the Ti .
calcination was used to prepare the carbon coated Ti ꢀdoped
18
3+
23
In addition, the Ti either on the surface or in the bulk of TiO
TiO2 nanocrystals. Firstly, 31 g titanium isopropoxide was
2
1
8
are usually not stable enough and easily oxidized by H O or O .
added to 6.8 g acetic acid with magnetically stirring for 15 min at
2
2
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room temperature. After that, the mixture was added drop by drop
into 160 mLꢀvigorousꢀstirring distilled water. Due to the
hydrolysis of titanium isopropoxide, a suspension was made.
equation, indicating that no obvious change in particle size
occurred during the washing and annealing processes (Table S1
of ESI†). It was worth pointing out that the sample Aꢀ550 was
After stirring for 1 h, 2 mL 65 wt% HNO was added into the 60 anatase phase, but the sample Bꢀ550 exhibited a mixture phase of
3
o
5
0
5
0
5
0
5
0
5
0
5
suspensions and then were heated at 75 C for 80 min for
obtaining a colloid solution. Then, about 40 mL distilled water
was added and the resulting solution was transformed to a 300ꢀ
rutile (JCPDS No. 21ꢀ1276) and anatase. This probably resulted
from that surface organics from the hydrolysis of titanium
isopropoxide on the sample A suppressed the phase transition to
o
21, 24
mL titanium autoclave and heated at 250 C for 12 h to obtain the
occur, as demonstrated in the previous reports.
3
+
organics coated Ti ꢀdoped TiO nanocrystals (denoted as sample
65
2
1
1
2
2
3
3
4
4
5
5
A). For obtaining a thinner organics coating layer (Fig.S1, ESI†),
sample A was washed by 1M NaOH for four times and then by
ethanol and distilled water twice separately to partially remove
the surface organics (denoted as sample B). Both the two samples
were freezeꢀdrying to remove the remained water. Both the
o
samples A and B were calcined at 350 and 550 C for 4 h with a
o
heating rate of 5 C/min in Ar for the carbonization of surface
organics. According to the heating temperature, the
corresponding products were marked as sample Aꢀ350, Aꢀ550, Bꢀ
3
50 and Bꢀ550, respectively.
Fig.1 XRD patterns for samples A, Aꢀ350, Aꢀ550, B, Bꢀ350 and Bꢀ550 (a).
Phases of all the samples were identified by a powder Xꢀray
TGꢀDSC of sample A in air (b).
diffraction (XRD, Ultima III, Rigaku Corp., Japan) using Cu Kα
λ=1.54178 Å, 40 kV, 40 mA) with a scan rate of 10 º/min. The
(
7
7
8
8
9
9
0
5
0
5
0
5
TGꢀDSC analysis was performed to understand the thermal
stability of sample A and the result was shown in Fig.1b. There
diffuse reflectance spectroscopy were collected using a UVꢀ
visible spectrophotometer (Shimadzu Corp., UVꢀ2500PC, Japan).
Xꢀray photoelectron spectroscopy (XPS) was carried out on
Thermo ESCALAB 250 spectrometer (Al Kα), and the
photoelectrons were detected by a hemispherical analyzer
operating at a passive energy of 20 eV. The binding energy was
calibrated on the reference C 1s peak at 284.8 eV. The highꢀ
resolution transmission electron microscopy (HRꢀTEM) analysis
was conducted using a JEOL 3010 transmission electron
o
was a wide endothermic peak from 200 to 400 C in the DSC,
which could be assigned to the burning of surface organics. A
o
narrow endothermic peak at 420 C corresponded to the phase
transformation from anatase to rutile phase. This evidence
o
meaned that the samples Aꢀ350 and Bꢀ350 prepared at 350 C
were pure anatase phase and the carbon coating can be formed on
the surface by carbonization of surface organics. The samples Aꢀ
o
5
50 and Bꢀ550 prepared at the 550 C, which was much higher
microscope.
Electron
paramagnetic
resonance
(EPR)
than the phase transformation temperature, should be a mixture
phase. However, XRD pattern of the sample Aꢀ550 did not
exhibit obvious rutile phase, probably due to that the content of
rutile phase was lower than the XRD detection limitation (5% for
volume percentage), resulting from the suppression effect of
measurement was carried out on a Bruker EMXꢀ10/12 EPR
spectrometer with a frequency of 9.8485 GHz at the room
temperature. The massꢀnormalized EPR spectra were from the
intensity of measured EPR signal dividing the mass of the sample.
The qualitative EPR analysis was carried out on a JEOL JESꢀ
FA200 spectrometer with a frequency of 9.0615 GHz at 77K.
The thermogravimetricꢀdifferential scanning calorimetry analysis
(TGꢀDSC) was performed using a thermoanalytical apparatus
21
surface organic layer. Indeed, heating the sample A after
partially removing the surface organics by washing would
produce a product with a mixture phase (sample Bꢀ550). The
weight fraction of rutile content in sample Bꢀ550 was calculated
by the Scherrer’s equation of W = I /(I +0.079I ), where W
(
STA 449C, NETZSCH) under an air atmosphere at a heating
o
R
R
R
A
A
rate of 5 C/min.
was the weighted fraction of anatase in the mixed phase, and IA
and I were the integrated intensity of corresponding anatase (101)
R
Results and Discussion
25
and rutile (110) diffraction peaks, respectively. The calculated
WR was 0.1 for sample Bꢀ550, confirming that the surface
organics can suppress the phase transition compared to the
sample Aꢀ550.
The XRD patterns of the samples prepared by hydrothermal
treatment with or without sequent calcination were shown in
Fig.1a. It could be found that, except for sample Bꢀ550, which
was a mixture phase of rutile and anatase, all the other samples
were anatase (JCPDS No. 21ꢀ1272). As the annealing
temperature rose, the crystallinity of the samples had no obvious
The TEM observations (Fig.2a and Fig.S2 in ESI†) showed
that these samples were 20ꢀ30 nm nanocrystals, in good
agreement with the XRD calculations. The HRꢀTEM crystal
lattice fringes (Fig.2bꢀd) of the whole nanocrystal indicated that
change. This indicated that the crystalline anatase TiO was
2
1
00 these asꢀprepared samples were single crystals. A 2ꢀ3 nmꢀthick
formed during the hydrothermal treatment. The calcination did
not change the phase structure and crystallinity if the heating
amorphous layer was observed on the surface of the sample Aꢀ
o
o
350 (Fig.2b). Increasing the temperature to 550 C, thickness of
temperature was below 550 C. The average sizes of the TiO2
the amorphous layer decreased to about 1 nm due to the
particles were estimated to be 20ꢀ30 nm according to Scherrer’s
2
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decomposition or/and carbonization of organics at high 25 much better. These observations implied that the organics existed
temperature (Fig.2c), as demonstrated in DSC. However, no
amorphous layer is visible on the surface of sample Bꢀ350
on the surface of sample A. According to the TG result, the
content of surface organics was about 3.89 % of the total mass of
TiO2 nanocrystals. The isopropanol was detected by liquid
chromatography during the hydrolysis of titanium isopropoxide,
(Fig.2d), which convinced that the surface organics could be
5
washed away by the NaOH solution and ethanol.
3
3
4
0
5
0
which can be the main source of organics absorbed on the surface
o
of TiO . After heating the sample A at 350 C, the contents of ꢀ
2
COOH and CꢀOH decreased and a new C 1s peak at 284.3 eV
appeared and can be assigned to the C=C in the graphiticꢀphase
26
carbon (Fig.3b), originating from the carbonization of organics.
With increasing the heat temperature, the content of graphiteꢀ
phase carbon increased due to the increase of carbonized degree
of organics (Fig.S2, ESI†).
Three peaks were observed in the Ti 2p XPS spectrum of
4
+
sample A (Fig.3c). Peaks at 458.6 eV and 464.3 eV were Ti
2p and 2p . A lowꢀintensity peak at 457.4 eV was assigned to
3
/2
1/2
33
3+
3+
Ti 2p3/2
,
confirming that the Ti formed on the surface of
3+
TiO nanocrystals. The content of Ti slightly decreased after
heating sample A at 350 C due to its thermal instability (Fig.3d).
Sample Bꢀ350 exhibited much lower intensity of Ti XPS peak
than sample Aꢀ350 (Fig.S3, ESI ), meaning that the surface
2
o
3
+
4
5
†
3+
organics could partially prevent oxidation of Ti during the
annealing. However, no peak at 457.4 eV was found when the
o
sample A or B was heated at as high temperature as 550 C
Fig.2 TEM morphology of sample A (a). HRꢀTEM images for the samples Aꢀ
3+
(
Fig.S2, ESI
†
), instructing that the surface Ti was completely
3
50 (b), Aꢀ550 (c) and Bꢀ350 (d).
32
50
oxidized at such high temperature.
1
0
Fig.4 Normalized EPR spectra for Aꢀ350, Bꢀ350, Aꢀ550 and Bꢀ550. Inset
Fig.3 XPS spectra for C 1s and Ti 2p in sample A (a, c) and in sample Aꢀ350
b, d).
shows the normalized EPR spectra for samples A and B.
(
55
The EPR analysis is a useful tool to distinguish the surface
3
+
1
5
XPS measurement was performed for further confirming the
surface composition of asꢀprepared samples. The C 1s XPS
spectrum of sample A was shown in Fig.3a and can be divided
and bulk Ti . The observed g values in the sample A were 1.959
and 1.986, corresponding to the g and g (inset in Fig.4), are a
||
⊥
3+
clear indication of Ti doping into the bulk of TiO during the
into three peaks. The peak at 284.8 eV was mainly attributable to 60 hydrothermal reaction. The CꢀOH in the isopropanol from the
2
8
amorphous CꢀC bonding, 285.5 eV to the CꢀOH and 288.4 eV to
ꢀCOOH. Although sample B were washed by 1M NaOH,
ethanol and distilled water, the XPS spectrum of C 1s (Fig.S1b of
hydrolysis of titanium isopropoxide was considered to be a good
reducer for reducing Ti to Ti . In our case, the growth of
26
4+
3+ 33
2
0
TiO single crystal was kinetically slow in the presence of acetic
2
32
ESI
†
) still showed the existence of C–OH and –COOH, which
acid buffer solution. We believe that the isopropanol reducing
4+
3+
had been reported that the C–OH and –COOH were strong 65 Ti to Ti occurs during the whole growing process of TiO
anchoring groups on the surface of TiO2,
2
2
7ꢀ28
3+
and –COOH was
single crystal, thus forming a Ti bulkꢀdoped TiO
2
. In order to
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3
+
determine the concentration of Ti in the TiO2 catalyst, the
carbonized degree of surface organics. The gradual increasing
quantified EPR analysis was carried out. A qualitative EPR 45 color of samples (inset of Fig.5) further confirmed that the
analysis through double integration of the peak relative to that of
a 3d signal of Mn , showed that the concentration of Ti was
content increase of graphiteꢀphase carbon with increasing the heat
temperature, which would induce the strong background
absorption. The content of graphiteꢀphase carbon on sample Bꢀ
5
2+
3+
5
0
5
0
5
about 0.0033% of all the Ti centers in the TiO , which was the
2
1
1
comparable level with the reported results. An EPR signal at
350 or Bꢀ550 was obviously lower than that on the sample Aꢀ350
ꢀ
10
3+
g=2.026 represented the existence of the surface O , which 50 or Aꢀ550, confirming that the surface organics on Ti ꢀdoped
2
3
+
suggested that Ti also formed on the surface of TiO . For the
TiO indeed can be partially removed by chemical washing.
2
2
3+
samples Aꢀ350, Bꢀ350 and Aꢀ550, the surface Ti signal
disappeared due to its thermal instability and a strong EPR signal
at g=2.004, assigning to the formation of surface oxygen
vacancies. As annealing in the atmosphere without oxygen
could generated more oxygen vacancies by eliminating surface
1
1
2
2
10
8
oxygen atoms, largely enhancing EPR signal of oxygen
vacancies. The locally enlarged observations on Fig. 4 indicated
3
+
that the signal of bulk Ti became weak lightly after the heat
o
treatment (Fig.S7 of ESI†). All the samples calcined at 550 C
3
+
showed much weak intensity of Ti in the bulk, due to that the
3+
Ti was very sensitive to heating. Sample Aꢀ350 shows much
3
+
higher intensity of oxygen vacancies on the surface and Ti in
the bulk than sample Aꢀ550, indicating that at higher temperature
surface oxygen vacancies can be oxidized by oxygenꢀcontaining
3
+
4+
organics and the bulk Ti transformed to Ti by losing the
excess electron that was withdrawn by interstitial or surface
36
oxygen adatoms.
3+
Fig.6 Photocatalytic hydrogen generation over the carbon coated Ti ꢀdoped
TiO under irradiation of visible light (λ≥420 nm).
55
2
The photocatalytic hydrogen production was performed by
dispersing 0.1 g catalyst in a mixture solution of 220 mL distilled
water and 50 mL CH OH. 0.5wt% Pt coꢀcatalyst was loaded onto
3
3
+
60
the surface of the Ti ꢀdoped TiO by photoꢀdeposition method
2
33
under the full arc irradiation of Xe lamp for 2 h. As shown in
Fig.6, sample Aꢀ350 showed the highest and most stable activity
of hydrogen production with a slope of 1 ꢁmol/h, within the 12 h
visible light irradiation (Fig.S4 of ESI ). Sample A, Aꢀ550, B, Bꢀ
†
6
7
7
8
5
0
5
0
350 and Bꢀ550 got the slopes of 0.6, 0.75, 0.4, 0.6 and 0.7 ꢁmol/h
respectively in the first 2 h, but they all suffered a gradually
decreased activity during the sequential 10 h. Due to the
coexistence of rutile and anatase phase, sample Bꢀ550 exhibited a
better photoꢀactivity than sample B and Bꢀ350, probably resulting
from the improved charge separation efficiency by heterojunction
Fig 5. UVꢀVis absorption spectra of the asꢀprepared samples A, B, Aꢀ350, Bꢀ
50, Aꢀ550 and Bꢀ550. For comparison, UVꢀVis spectrum of the commercial
anatase TiO was also shown here.
42,43
3
effect.
Except for sample Bꢀ550, all the samples with carbon
30
35
40
2
coating layers showed better activity in hydrogen generation than
those without carbon coating layers under the visible light
irradiation. Sample Aꢀ350 contained 2.1wt% carbon on the
surface, which was determined by TG (Fig.S6 of ESI†), showed
the best activity and stability of utilizing visible light of
generating hydrogen. As the reported results, the carbon layer
coated on the surface of catalyst decreased the light absorption,
The optical properties for these asꢀprepared samples were
checked by UVꢀVis spectrophotometer, as shown in Fig.5. The
absorption spectra for all the samples shifted to a longer
wavelength revealing a decrease in the band gap. Meanwhile, the
absorbance in the visible range was enhanced, compared to the
stoichiometric anatase. This phenomenon was consistent with the
34ꢀ39
but enhanced the adsorption of CH OH.
of carbon coating on the surface of anatase TiO was reported to
An optimal amount
3
3+
theoretical calculation, owing to that an electronic band from Ti
2
doping was located just below the conduction band of pure TiO2.
be 3.5wt% for the best photoꢀactivity for decomposition of
3
9
It was obvious that these asꢀprepared samples exhibited
methylene blue, owing to the improved dye adsorption. In
addition, the carbon coating layer could work as a barrier layer
significant differences in the background absorption. With
increasing the heat temperature, the background absorption of
both the sample A and B increased due to the increase of
3+
19,20
avoiding the oxidation of Ti from H O or O ,
enhancing the
2
2
4
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3
+
stability of Ti in TiO . It is obvious that the difference in ability
surface of the asꢀprepared nanocrystals. After the calcination
treatment in Ar, a carbon layer formed by the carbonization of the
2
of hydrogen generation for the five anatase samples under visible
light irradiation mainly originated from the different 50 surface organics, which was an effectively protective layer to
3
+
3+
concentrations of bulk Ti , which could narrow the band gap for
more visible light absorption by inserting an impurity level below
avoid directly exposing the surface of Ti ꢀdoped TiO into
2
3
+
5
oxygenꢀrich environment. Therefore, the carbon coated Ti ꢀ
doped TiO2 exhibited excellent stability for photocatalytic
hydrogen production under visible light irradiation. Our results
demonstrated that the carbon coating is a simple method for
the conduction band of TiO , and the different stability must
reflect the different protection ability of the surface carbon layers.
2
55
3+
developing the stable and efficient Ti ꢀdoped TiO photocatalyst.
2
Acknowledgments
60
This work is supported by the National Basic Research Program
of China (2013CB632404 and 2011CB933303), the National
Natural Science Foundation of China (11174129, 51272101 and
6
1377051), the Science and Technology Research Program of
Jiangsu Province (BK20130053) and the State Key Laboratory of
NBC Protection for Civilian. (No. SKLNBC2014ꢀ09).
65
1
0
Fig.7 Normalized EPR spectra of samples Aꢀ350, Bꢀ350 (a) and Aꢀ550, Bꢀ550
(b) before and after 12 h visible light irradiation.
Notes and references
a
The excellent stability of photoactivity for the asꢀprepared
National Laboratory of Solid State Microstructures & Ecomaterials
3
+
carbon layer coated Ti ꢀdoped anatase TiO2 was also
demonstrated by 36 h light irradiation (Fig.S5 of ESI ), which
was a direct evidence to reflect the high stability of sample Aꢀ350
and Renewable Energy Research Center (ERERC) at Department of
Physics, Nanjing University, Nanjing 210093, P.R.China, Email:
yutao@nju.edu.cn
1
5
†
7
0
3+
b
College of Engineering and Applied Sciences, Nanjing University,
during the photoreaction. To confirm the stability of Ti in
sample Aꢀ350, the qualitative EPR analysis was carried out to
evaluate the concentrations of surface oxygen vacancies and bulk
2
c
10093, P.R.China, Email: yscfei@nju.edu.cn
Collaborative Innovation Center of Advanced Microstructures,
3
+
Nanjing University, Nanjing 210093, P.R.China
d
2
2
3
3
4
0
5
0
5
0
Ti of the asꢀprepared samples before and after photocatalytic
1
0,18
75
Jiangsu Key Laboratory for Nano Technology, Nanjing University,
hydrogen generation reaction,
as shown in Fig.7. Indeed, both
Nanjing 210093, P.R.China
of the samples Bꢀ350 and Bꢀ550 without carbon coating layer
exhibited the obvious decrease in EPR signal for both of surface
†
Electronic Supplementary Information (ESI) available: Details of
experimental procedures, characterizations, and supporting images. See
DOI: 10.1039/c000000x/
3
+
oxygen vacancies and bulk Ti after 12 h photoꢀreaction. No
visible difference in EPR peak intensity was observed for sample
Aꢀ350 with carbon coating layer before and after photoꢀinduced
hydrogen production reaction, demonstrating that the carbon
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1
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coating layer as a barrier layer avoided directly exposing the
7
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In summary, the stable carbon coated Ti ꢀdoped anatase TiO
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2
1
7.
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titanium isopropoxide. We found that isopropanol, the hydrolysis
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