生态环境 2006, 15(4): 720-723
Ecology and Environment
http://www.jeesci.com
E-mail: editor@jeesci.com
The Photodegradation of 2-mercaptobenzothiazole in the suspension of nitrogen-doped titania under visible light
QIN Haoli 1, 2, GU Guobang 1, LIU Song 1
1. College of Chemistry, South China University of Technology, Guangzhou 510640, China;
2. College of Science, Guizhou Normal University, Guiyang 551000, China
Abstract: In order to utilize visible light in photocatalytic reaction, yellow nitrogen-doped titania were prepared by sol-gel method in
mild condition, with the elemental nitrogen source from aqua ammonia. The catalysts were characterized by XRD, TEM, XPS, and
UV-Vis diffuse reflectance spectrophotometer. The analytical results demonstrated that all catalysts were anatase, and the crystallite
size of nitrogen-doped titania increased with increasing of N/Ti proportioning, and the doping of nitrogen could extend the absorption
shoulder into the visible light region. With a purpose of odor control, 2-mercaptobenzothiazole (MBT) was used in this study as a
model chemical, and photocatalytic activities of the nitrogen-doped titania were investigated based on the MBT photodegradation in
aqueous solution under visible light. The experimental results showed that the photocatalytic activity of nitrogen-doped titania were
nearly 3 times higher than that of the commercial titania photocatalyst Degussa P-25 for MBT degradation under visible light irradiation. In addition, there was an optimum N/Ti proportioning to exhibit the highest visible-light activity.
Key words: titania; 2-mercaptobenzothiazole; nitrogen-doped; visible light
CLC number: X13
Document code: A
Article ID: 1672-2175（2006）04-0720-06
Titania is well known as a cheap, stable, nontoxic,
and efficient photocatalyst without secondary pollution. However, because of the relatively high intrinsic
band gap of anatase TiO2 (3.2 eV), only 4% of the
incoming solar energy on the earth’s surface can be
utilized. On the other hand, the hole and electron excitated by the UV light can recombine easily, which
will reduce the efficiency of photons. It has been one
of the most challenge topics that how to reduce the
band gap to produce the visible-light photocatalysis
and suppress the recombination of hole-electron
pairs[1]. Therefore, considerable efforts have been
made to extend the photoactivity of titania-based systems further into the visible light region, using dopants.
Regarding nitrogen-doped titania, Sato[2] reported
for the first time that a titania-based material from the
mixtures of a commercial titanium hydroxide and
ammonium calcined at about 400 ℃ showed higher
photocatalytic activity in the visible light region. Asahi et al[3] reported that nitrogen-doped titania could
induce the visible-light activity in which nitrogen atoms substituted small quantity of oxygen atoms
(0.75%), and the doped nitrogen was responsible for
the visible light sensitivity due to the narrowing of the
band gap by mixing the N2P and O2P states. It has initiated a new research area to extend the photo absorbance into visible light region using nitrogen-doped
titania. Nitrogen-doped titania have been produced
through different techniques, such as hydrolytic process [4-7], mechanochemical technique[8-10], reactive
DC magnetron sputtering [11, 12], high temperature
treatment of titania under NH3 flow [3,13,14], sol-gel
method[15], solvothermal process [16] and calcination of
a complex of Ti4+ with a nitrogen-containing ligand[17].
Among these techniques, it is extremely difficult to
get anion-doped photocatalyst using wet-methods
such as sol-gel and co-precipitation, and rarely nitrogen-doped titania catalysts have been produced by
using sol-gel route. Burda et al [15] added triethylamine to the colloidal nanoparticle solution and heated
the samples to obtain nitrogen-doped titania with the
average grain size 6~10 nm, which can absorb well
into the visible region up to 600 nm, but the samples
must be prepared grindingly under low pH condition
and temperature as low as 2 ℃ through sol-gel process.
In this study, we incorporated nitrogen into titania by sol-gel method in mild condition, using tetrabutyl titanate as the titanium source and aqua am-
作者简介：秦好丽（1973－），女，讲师，博士研究生，研究方向为二氧化钛的可见光活性。Tel: +86-20-88371558；E-mail: hollyqin@126.com
收稿日期：2006-03-24
秦好丽等：可见光下氮掺杂二氧化钛对巯基苯并噻唑的降解
1
1.1
Experimental methods
Synthesis
In a typical preparation procedure, 17 ml of teter-n-butyl titanium (Ti(O-Bu)4) was dissolved in 40
ml of absolute ethanol and then this Ti(O-Bu)4 solution was added drop-wise under vigorous stirring into
55 ml of the mixture solution containing 40 ml of absolute ethanol, 10 ml glacial acetic acid, and 5 ml of
double-distilled water. The resulting transparent colloidal suspension was stirred for 0.5 hour and aged for
2 days till the formation of xerogel, then grounded
into powders. The powders were calcined at 400 ℃ for
2 h, then grounded in agate mortar and screened by
shaker to obtain fine titania powders finally (signed as
0#).
A series of nitrogen-doped titania (N-TiO2) catalyst were generated with the following procedure: different volumes aqua ammonia (corresponding different N/Ti proportioning of 2, 4, 6, 8, 10 mol% signed
as 1#, 2#, 3#, 4# and 5#, respectively) were added into
the resulting transparent colloidal suspension under
vigorous stirring and stirred for 1 hour, then aged for 2
days till the formation of xerogel. The following procedure was carried according to the pure titania.
1.2 Characterization
X-ray diffraction (XRD) were recorded using a
Shimadzu XD-3A diffractometer with Cu Kα1 radiation. An accelerating voltage of 30kV and emission
current of 30mA were applied. The absorption edges
of catalysts were determined from the onset of the
diffuse reflectance spectrum using a UV-Vis spectrophotometer equipped with an integrated sphere (Hitachi, UV-3010). The particle size and shape were
measured by transmission electron microscopy (TEM)
(JEM -100CXⅡ). The catalysts of X-ray photoelectron spectroscopy data were obtained through an ESCALab220i-XL electron spectrometer from VG Scientific under 300-W AlKα radiation. The base pressure was about 3×10-9 mbar. The binding energies
were referenced to the C1s line at 284.6 eV from adventitious carbon.
1.3 Photoreactor system
The photocatalytic activity of photocatalyst was
evaluated using the photocatalytic degradation of
MBT under 200-W tungsten halide lamp (THL) as the
visible-light source. The THL was out of the reactor.
The reactor was surrounded by a borosilicate glass
jacket with NaNO2 aqueous solution[18] (2 mol·L-1)
cycling inside. NaNO2 aqueous solution was used to
avoid the UV light. The MBT taken at given time intervals was centrifugally separated with 12 000 r/min,
then determined with a spectrophotometer by measuring the absorbance at 316.5nm. For comparison, a
photocatalytic reaction was also carried out using
commercial titania powers P25.
2
Results and discussion
2.1 Crystal phase composition and TEM
X-ray diffraction analyses indicated that the catalysts were anatase, shown in Fig. 1. Neither specific
peaks of Ti-N nor N-O was detected. Average grain
5#
Intensity /a.u.
monia as nitrogen source. The titania catalysts were
characterized by XRD, TEM, XPS, and UV-Vis diffuse reflectance spectrophotometer. The photocatalysts was found to be more active for MBT degradation under visible light irradiation compared to commercial titania photocatalyst Degussa P-25 (P25). The
effect of N/Ti proportioning on the visible-light-activity was also discussed.
721
4#
3#
2#
1#
0#
20
30
40
50
60
2 /degree
Fig. 1
XRD patterns of different titania catalysts
sizes calculated from the broadening of the (101) peak
of anatase phase were 7.2, 8.8, 12.6, 13.4, 14.4 and
15.5 nm for 0#, 1#, 2#, 3#, 4# and 5#, respectively.
The doping of elemental nitrogen resulted in the enlargement of the crystallite size, and the crystallite
size increased with increasing of N/Ti proportioning.
Fig. 2 showed TEM photographs of 0# and 2#
catalyst. The 0# catalyst possessed well-dispersed
5~15 nm particles, and 2# catalyst possessed 10~20
nm particles. This further demonstrated that the doping of nitrogen enlarged the particle size of titania,
which agreed with the results from the XRD patterns.
生态环境 第 15 卷第 4 期（2006 年 7 月）
722
(a)
(b)
Fig. 2
TEM photographs of titania catalysts
(a) the pure titania；(b) # 2
2.2 Diffuse reflectance spectrum of photocatalysts
The diffuse reflectance spectra of catalysts were
shown in Fig. 3. The same absorption edges were observed for 0# and N-TiO2, but noticeable shift of the
2.5
2.0
2#
3#
4# 5#
1#
0#
P25
Abs
1.5
1.0
0.5
0.0
300
350
400
450
500
550
N/Ti proportioning caused different optical absorption
intensity. In addition, the color of P25 was snow-white
and color of pure titania (0#) was white, whereas that
of N-TiO2 was yellow. It implied that the optical absorption intensity had something to do with the shade
of color, the darker the color, the higher the optical
absorption intensity.
2.3 XPS Studies
The N1S X-ray photoelectron spectroscopy (XPS)
of the pure titania 0#, 2# and 5# were showed in Fig. 4.
The samples of 2# and 5# all displayed a relatively
weak peak at about 396.2 eV (Fig. 4), which had previously been found to result from Ti-N bonds3,13. The
600
Wavelength /nm
UV-Visible absorption spectra of titania catalysts
prepared by sol-gel and P25
absorption shoulder extending to the visible light region were observed for N-TiO2 catalyst. Asahi et al [3]
and other investigators [8,10,16] reported that the optical
absorption edge shifted to visible-light region and
proved that mixing the N 2P and O 2P states narrowed
the band gap. However, our results were different
from theirs. The UV-Vis spectra was proved that an
isolated narrow N 2P band above the valence band[13],
so there were no shift of the optical absorption edge
between N-TiO2 and 0#. Compared to P25, the catalysts prepared by the sol-gel method exhibited larger
absorption edge shifted to the visible light region and
higher optical absorption intensity. The order of optical absorption intensity showed in Fig.3 was 2#, 3#,
4#～5#, 1#, 0# in turn, which indicated that different
5#
Relative Intensity / a.u.
Fig. 3
2#
0#
394
396
398
400
402
404
406
Band Energy /eV
Fig. 4
XPS spectra of N1S taken on the surface of catalysts
nitrogen was substituted for oxygen in the TiO2 lattice
and the substitutional β-N states peaking at 396 eV13
are the photoactive sites under visible light since N 2P
states contribute to the formation of a narrow N 2P
band close to the valence band. Due to the different
N/Ti proportioning, the peak of 5# at 396.2 eV was
stronger slightly than that of 2#. The peak around 400
秦好丽等：可见光下氮掺杂二氧化钛对巯基苯并噻唑的降解
eV was chemisorbed γ-N23, 13. The pure titania 0#
displayed a weak peak at 400 eV derived from pollution of N2 during the measurement.
NOx generated by oxidation of nitrogen during
the heat-treatment would escape from the titania lattice which induced the loss of nitrogen. Actually, the
residual nitrogen content in the titania lattice was
smaller greatly than the N/Ti proportioning in synthesis process, only 0.89 and 0.93 at.% (calculated by
XPS) for 2# and 5#, respectively, which implied absolute majority of nitrogen lost during heat-treatment.
The Ti2p XPS spectra of three catalysts were
shown in Fig. 5. It can be seen that the Ti2p XPS of 2#
showed a slight deformation in the direction of lower
723
Table 1 Peak parameters for Ti2p XPS spectrum
taken on the surface of catalysts
Ti3+2p3/2
Sample
B.E
FWHM
Area
B.E
FWHM
/eV
/eV
/%
/eV
/eV
/%
0#
458.71
1.09
0.46
459.20
1.04
99.54
2#
458.49
1.11
1.93
458.99
0.96
98.07
5#
459.31
1.13
2.41
459.78
1.11
97.59
Area
amount of Ti3+ existing on the surface of catalysts increased with the increase of nitrogen content. The fitting peaks at 458.99~ 459.78 eV represent Ti4+.
2.4 Evaluation of Photocatalytic Activity
Fig. 6 showed degradation of MBT in the presence of various titania catalysts under visible irradiation. The MBT degradation of blank test without any
5#
2#
0#
Relative Intensity / a.u.
Ti4+2p3/2
1.0
0.8
C/C0
0.6
0.4
0.2
0.0
454
456
458
460
462
464
466
468
-50
B
B
B
B
B
B
B
B
0
50
100
Fig. 5
XPS spectra of Ti2p taken on the surface of catalysts
150
200
250
300
350
t /min
Binding Energy /eV
Fig. 6
Degradation of MBT with different photocatalysts
under visible light
binding energy and 5# showed a slight deformation in
the direction of higher binding energy, corresponding
to the different oxidation states of titanium. Each contribution consisted of a doublet, Ti2p3/2 and Ti2p1/2
peaks. In general, the area ratio of the two peaks,
A(Ti2p1/2)/A(Ti2p3/2), was equal to 0.5 and the binding
energy difference, △Eb＝Eb(Ti2p1/2)－Eb(Ti2p3/2), was
always 5.7 eV19. In our investigation, the Ti 2p3/2 peak
was fitted into two peaks of Ti4+ and Ti3+. The binding
energy, full width at a half of the maximum height of
peaks (FWHM) and the percentage were listed in Table 1. The charge imbalance caused by nitrogen entering into the lattice of titania during heat-treatment
formed oxygen vacancy which further reduced Ti4+ to
Ti3+. For the Ti 2p3/2 peak of 0#, there was an almost
negligible peak at 457.54 eV attributed to Ti3+ because
residual carbon could reduce Ti4+ to Ti3+ during
heat-treatment slightly. As listed in Table 1, the
photocatalysts was zero. It was obviously that the visible-light activities of N-TiO2 were better than that of
P25 and pure one. The 2# catalyst demonstrated the
highest visible-light activity, the figure-of-merit was
nearly 3 times as that of P25. The little nitrogen content of 1# caused its lower visible light activity compared with the other N-TiO2 catalysts. While in the
range of 4～10 mol% (N/Ti proportioning), the visible-light activity decreased appreciably with increasing of N/Ti proportioning.
It was found in this study that the crystal composition of the photocatalysts was anatase. Alternatively
the modification of the surface state of the catalysts
might be another critical reason for promoting the effective separation of electron-hole pairs and photoactivity. In the nitrogen-doped titania catalysts, the oxygen sites were partially replaced with nitrogen atoms
while TiO2 was simultaneously reduced[20]. These
生态环境 第 15 卷第 4 期（2006 年 7 月）
724
changes caused an increase in oxygen vacancy and
amount of Ti3+. The oxygen vacancy and Ti3+ species
act as hole traps. While the electrons and holes were
generated in the initial stage of visible light illumination, the defects on the titania surface or in the bulk
could suppress the recombination of electron-hole
pairs and hence extend their lifetime[21]. As the concentration of dopant increased, the surface barrier becomes higher, and the space charge region becomes
narrow. The electron-hole pairs within the region were
efficiently separated by the large electric field. At
some degree, the higher content of Ti3+ on the surface
of N-TiO2 than that of pure titania would be one of
significant reasons to change their photocatalytic
properties and to enhance their photoactivity. However,
there must be an optimal content of Ti3+ existing on
the nitrogen-doped titania. When the concentration of
dopant was excessively high, the space charge region
became very narrow and the penetration depth of light
into titania greatly exceeded the space charge layer;
therefore the recombination of the photogenerated
electron-hole pairs became easier22. Here, excessive
oxygen vacancy and Ti3+ acted as a recombination
center for holes and electrons，which would decrease
the photoactivity. Therefore, the presence and optimal
content of Ti3+ might be the critical factors leading the
improvement of the photoactivity. In this study, it was
obviously that difference of nitrogen content between
2# and 5# calculated by XPS was very small, which
just agreed with the tiny difference of photoactivity.
On the other hand, with increasing of N/Ti proportioning, crystallite size increased and adsorption area
decreased, which could not be neglected to influence
the visible light activity of catalysts.
3
There was an optimum N/Ti proportioning at 4 mol%
to exhibit highest visible-light activity.
References:
[1] Vinodgopal K, Kamat P V. Enhanced rates of photocatalytic degradation of an azo dye using SnO2/TiO2 coupled semiconductor thin
filmsJ. Environmental Science Technology, 1995, 29(3): 841-845.
[2] Sato S. Photocatalytic of NOx-doped TiO2 in the visible light regionJ.
Chemical Physics Letters, 1986, 123: 126-128.
[3] Asahi R, Morikawa T, Ohwaki T, et al. Visible-light photocatalysis in
nitrogen-doped titanium oxidesJ. Science, 2001, 293: 269-271.
[4] Sakatani Y, Koike H, Koike H. Titanium oxide, photocatalyst comprising same and photocatalytic coating agent[P]. JP 2001072419,
2001-01-03.
[5] Ihara T, Miyoshi M, .Iriyama Y, et al. Visible-light-active titanium
oxide photocatalyst realized by an oxygen-deficient structure and nitrogen dopingJ. Applied Catalysis B: Environmental, 2003, 42:
403-409.
[6] Noda H, Oikawa K, Ogata T, et al. Preparation of Titanium(Ⅳ) oxides
and its characterizationJ.The Chemical Society of Japan, 1986, 8:
1084-1090.
[7] Salthivel S, Kisch H. Photocatalytic and photoelectrochemical properties of nitrogen-doped titanium dioxide J. CHEMPHYSCHEM, 2003,
4: 487-490.
[8] Yin S, Yamaki H, Komatsu M, et al. Preparation of nitrogen-doped
titania with high visible light induced photocatalytic activity by
mechanochemical reaction of titania and hexamethylenetetramineJ.
Journal of Materials Chemistry, 2003, 13: 2996-3001.
[9] S. Yin, H. Yamaki, Q.W. Zhang, et al. Mechanocehnimal synthesis of
nitrogen-doped titania and its visible light induced NOx destruction
abilityJ. Solid State Ionics, 2004, 172: 205-209.
[10]
Catalysis B: Environmental, 2004, 52 (1): 11-21.
[11] Lindgren T, Mwabora J. M, Avendano E, et al. Photoelectrochemical
and optical properties of nitrogen doped titanium dioxide films prepared by reactive DC magnetron sputteringJ. Journal of Physical
Chemistry B, 2003, 107: 5709-5716.
[12] Chen Songzhe, Zhang Pengyi, Zhu Wanping, et al. Nitrogen states
and photocatalytic activity of nitrogen-doped TiO2 films prepared by
Conclusions
Yellow nitrogen-doped titania catalysts, with the
elemental nitrogen source from aqua ammonia, were
prepared using sol-gel method in mild condition. The
crystallite size of anatase nitrogen-doped titania were
larger than the pure one, and increased with increasing
of N/Ti proportioning. The nitrogen incorporation in
the lattice of TiO2 formed a narrow N2P band above
the valence band which exhibited higher visible light
absorption and was responsible for the visible-light
activity. The amount of oxygen vacancy and Ti3+ on
the surface of catalysts, crystallize size and adsorption
area were all factors to influence the photoactivities.
Wang JS, Yin S, Komatsu M, et al. Photo-oxidation properties of
nitrogen doped SrTiO3 made by mechanical activationJ. Applied
reactive magnetron sputteringJ. Chinese Journal of Catalysis, 2004,
25(7): 515-517.
[13]
Irie H, Watanabe Y, Hashimoto K. Nitrogen-concentration dependence on photocatalytic activity of TiO2-XNX powdersJ. Journal of
Physical Chemistry B, 2003, 107: 5483-5486.
[14]
Diwald O, Thompson T L, Zubkov T, et al. Photochemical activity of
nitrogen-doped rutile TiO2 (110) in visible lightJ. Journal of Physical Chemistry B, 2004, 108: 6004-6008.
[15] Burda C, Lou Y, Chen X, et al. Enhanced nitrogen doping in TiO2
nanoparticlesJ. Nano Letters, 2003, 3(8): 1049-1051.
[16]
Aita Y, Komatsu M, Yin S, et al. Phase-compositional control and
visible light photocatalytic activity of nitrogen-doped titania via solvothermal processJ. Journal of Solid State Chemistry, 2004, 177:
3235-3238.
[17]
Sano T, Negishi N, Koike K, et al. Preparation of a visible
秦好丽等：可见光下氮掺杂二氧化钛对巯基苯并噻唑的降解
725
light-responsive photocatalyst from a complex of Ti4+ with a nitro-
[20] Shin C H, Bugli G, Mariadssou G D. Preparation and characterization
gen-containing ligandJ. Journal of Materials Chemistry, 2004, 14
of titanium oxynitrides with high specific surface areasJ. Journal of
(3): 380-384.
Solid State Chemistry, 1991, 95: 145-155.
[18] Christian L, Kunt H, Horst K, et al. Visible light photodegradation of
[21]
4-chlorophenol with a coke-containing titanium dioxide photo-
application to the removal of various types of aqueous pollutantsJ.
catlystJ. Applied Catalysis B: Environmental, 2001, 32: 215-227.
[19]
Yu J G, Yu J C, Cheng B, Zhao X J. Photocatalytic activity and char-
Linsebiger A L, Lu G, Yatas J T. Photocatalysis: fundamentals and
Chemical Reviews, 1995, 95:735-758.
[22]
Li F B, Li X Z, Hou M F. Photocatalytic degradation of
acterization of the sol-gel derived Pb-doped TiO2 thin filmsJ. Jour-
2-mercaptobenzothiazole in aqueous La3+-TiO2 suspension for odor
nal of Sol-Gel Science Technology, 2002, 24: 39-48.
controlJ. Applied Catalysis B: Environmental, 2004, 48: 185-194.
可见光下氮掺杂二氧化钛对巯基苯并噻唑的降解
秦好丽 1, 2，古国榜 1，柳 松 1
1. 华南理工大学化学科学学院，广东 广州 510640；2. 贵州师范大学理学院，贵州 贵阳 551000
摘要：光降解反应中为了有效地利用可见光，以氨水为氮源，采用溶胶凝胶法在温和条件下制备出黄色氮掺杂二氧化钛。分
别采用 XRD、TEM、XPS 和 UV-Vis 漫反射光谱对样品进行了表征。结果表明，所制备的样品均为锐钛矿相，晶粒随 N/Ti
配比的增加而增大；氮掺杂进入二氧化钛晶格中使可见光吸收增强。为控制水处理过程中的气味问题，以巯基苯并噻唑为探
针，考察了氮掺杂二氧化钛的可见光活性。结果显示氮掺杂二氧化钛在可见光照射下可使巯基苯并噻唑的降解率为商用二氧
化钛 Degussa P-25 的 3 倍。此外，存在一个最佳 N/Ti 配比显示出最高的可见光活性。
关键词：二氧化钛；光催化；氮掺杂；可见光