Hydrothermal synthesis and characterization of TiO
2
nanorod arrays on glass
substrates
Yuxiang Li
a
, Min Guo
a
, Mei Zhang
a
, Xidong Wang
b,
*
a
Department of Physical Chemistry, University of Science and Technology Beijing, Beijing 100083, PR China
b
College of Engineering, Peking University, No. 5 of Yiheyuan Street, Haidian District, Beijing 100871, PR China
1. Introduction
TiO
2
-based one-dimensional structures, especially nanorod/
wire/tube arrays, have attracted much attention owing to their
excellent properties and important applications. Compared with
TiO
2
nanoparticles, TiO
2
nanorod/wire/tube arrays have lower
recombination rate for excited electron–hole pair, unique optical
and electric properties. Therefore, they can be widely applied in
many fields, such as photocatalyst, photovoltaic devices, solar

anodization of Ti foil which has 134
m
m in length, but it needs
high-purity polished titanium foil, which results in a high
production cost [14]. Moreover, the as-fabricated nanotubes are
amorphous and need to be annealed, which results in forming
polycrystalline TiO
2
structures and influencing their photoelectric
properties. Wu and Yu [15] synthesized well-aligned rutile and
anatase TiO
2
nanorods using CVD method. However, this method
involves the use of metal catalyst, high-temperature and vacuum
technique, which makes the preparation process complicated.
Compared to the above methods, hydrothermal synthesis of
TiO
2
nanorod arrays (TNAs) is a promising approach due to its
simple process, fast reaction velocity and low cost. Therefore, it is
fit for large-scale preparation of TNAs.
Up to now, preparing TNAs by hydrothermal approach is rarely
reported. Recently, Feng et al. [16] prepared TiO
2
nanorod films by
a low-temperature hydrothermal approach on a glass wafer
substrate. The as-prepared TiO
2
nanorod film looked like a pile
of radial papillae. Such morphology limits its applications in many

2
nanorod arrays grown on the pre-
treated glass substrate are well-aligned single crystal and grow along [0 0 1] direction. The average
diameter and length of the nanorods are approximately 21 and 400 nm, respectively. The photocatalytic
activity of TiO
2
nanorod arrays was investigated by measuring the photodegradation rate of methyl blue
aqueous solution under UV irradiation (254 nm). And the results indicate that TiO
2
nanorod arrays
exhibit relatively higher photocatalytic activity.
ß 2009 Elsevier Ltd. All rights reserved.
* Corresponding author. Tel.: +86 10 8252 9083; fax: +86 10 6275 7532.
E-mail address: [email protected] (X. Wang).
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Materials Research Bulletin
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doi:10.1016/j.materresbull.2009.01.009
effective means to control the growth of TNAs. Guo [17] and Wang
and co-workers [18] prepared well-aligned ZnO nanorod arrays by
pre-treating the ITO glass substrate, and the results indicated that
pre-treatment of the substrate played an important role for the
growth morphology of ZnO nanorod arrays.
In this study, the substrate was pre-treated by coating TiO
2
nanoparticles followed by heat treatment, and then the pre-treated
substrate (PT-substrate) was put into hydrothermal solution to
fabricate TNAs. The growth mechanism of TNAs and influence of
PT-substrate on the morphology of the prepared TNAs have been

2.4. Hydrothermal growth of TNAs
The hydrothermal precursor solution was prepared by mixing
0.05 M titanium trichloride (TiCl
3
) aqueous solution saturated
with sodium chloride. After the precursor solution was stirred for
5 min, it was transferred into a polytetrafluoroethylene vessel
which was placed in a sealed kettle, and then PT-substrate was
immersed into the precursor solution, and subsequently, the
hydrothermal growth of TNAs was carried out at 160 8C for 3 h.
2.5. Characterization
The morphology and size distribution of the as-prepared TNAs
were characterized by the field-emission scanning electron
microscopy (FE-SEM, ZEISS SUPRA
TM
55 operated at 10 keV).
Transmission electron microscope (TEM, PHILIPS-FEI TECNAI20)
and high-resolution TEM (HRTEM, JEM-2010) were used to further
elucidate the microstructure and phase characterization. X-ray
diffraction (XRD) analysis was performed with a Rigaku D
MAX
-RB
diffractometer using Cu K
a
radiation.
2.6. Photocatalytic activity measurement
The photocatalytic activity of TNAs was investigated by
measuring the photodegradation rate of methyl blue aqueous
solution. Photocatalytic reaction was carried out in a
200 ml quartz glass vessel under which there was an 18 W

This phenomenon can be explained that the glass substrate is
amorphous and the distribution of nucleation sites is not uniform.
After TiO
2
colloid solution is coated onto the glass substrate, the
surface is covered with a layer of compact TiO
2
nanoparticles.
Although TiO
2
nanoparticles are amorphous, they can provide
uniform heterogeneous nucleation sites effectively. Therefore, the
as-prepared TiO
2
nanorods have relatively better growth orienta-
Fig. 1. FE-SEM images of TNAs grown on the unmodified glass substrates at a hydrothermal growth temperature of 160 8C and growth time of 3 h. (a) Unmodified glass
substrate; (b and c) top view at different magnifications of TNAs.
Y. Li et al. / Materials Research Bulletin 44 (2009) 1232–1237
1233
tion and density distribution compared with those grown on the
unmodified substrate.
Fig. 3 shows XRD patterns of the different substrates, which
identify the phase structure of the substrates. From Fig. 3, it can be
seen that a wide peak in the angle range of 2
u
= 15–358 appears in
all XRD patterns, which is due to the influence of amorphous phase
of the glass substrate. Fig. 3a is XRD patterns of the unmodified
glass substrate, and no other peaks appear. Fig. 3b shows XRD
patterns of the substrate with pre-coated TiO

Fig. 4 shows XRD patterns of standard rutile phase (JCPDS No.
04-0551), standard anatase phase (JCPDS No. 01-0562) of TiO
2
and
TNAs grown on the different substrates. Fig. 4a shows XRD patterns
of TNAs grown on the unmodified glass substrate, which shows
that the main phase is rutile phase of TiO
2
. It can be seen from
Fig. 4b that the intensity of 1 1 0 peak of rutile phase increases
when TNAs grew on the substrate with pre-coated TiO
2
nanoparticles but not annealed. As shown in Fig. 4c, after the
pre-coated substrate was annealed, the diffraction intensity of
(1 1 0) planes increases even significantly. A number of works [19–
22] have reported that the prepared TiO
2
rods via hydrothermal
approach in strongly acidic solution are usually pure rutile phase.
This is in consistent with the results of XRD in this work. However,
a small part of anatase phase of the as-prepared TNAs was detected
by XRD, which might be due to the coated TiO
2
nanocrystal
particles on the glass substrate. From Fig. 4, we also see that the
diffraction intensity ratio of (1 1 0) to (1 0 1) becomes larger than
that of the standard rutile phase of TiO
2
, indicating that the as-
prepared TNAs prefer to grow along the (1 1 0) planes.

2
nanorod arrays grown on the substrate
becomes poor.
In addition, the diameter distribution of TiO
2
nanorods grown
on PT-substrate is illustrated in Fig. 6. Statistics show that 70% of
Fig. 2. FE-SEM images of TNAs grown on the TiO
2
-coated substrate without heat treatment at a hydrothermal growth temperature of 160 8C and growth time of 3 h. (a) PT-
substrate without heat treatment; (b and c) top view at different magnifications of TNAs.
Fig. 3. XRD patterns of the different substrates. (a) Unmodified glass substrate; (b)
PT-substrate without heat treatment; (c) PT-substrate at an annealing temperature
of 700 8C.
Fig. 4. XRD patterns of standard rutile phase (JCPDS No. 04-0551), standard anatase
phase (JCPDS No. 01-0562) of TiO
2
and TNAs grown on: (a) unmodified glass
substrate; (b) PT-substrate without heat treatment; (c) PT-substrate at an annealing
temperature of 700 8C.
Y. Li et al. / Materials Research Bulletin 44 (2009) 1232–1237
1234
the nanorods have a diameter between 15 and 25 nm and the
average diameter of TiO
2
nanorods is about 21 nm. Compared with
the TNAs reported previously [11,16], the as-prepared TNAs in this
work have been improved in the growth orientation, the density
distribution and the aspect ratio.
It can be seen from XRD patterns and SEM images, that the

spacing between two fringes is 0.325 nm, corresponding to the
interplanar distance of the (1 1 0) index planes of the rutile TiO
2
,
indicating that the as-prepared TiO
2
nanorods via hydrothermal
approach are the rutile structure. Furthermore, it is observed that
the (1 1 0) crystal planes are perpendicular to the c-axis, implying
Fig. 5. FE-SEM images of TNAs grown on PT-substrate at an annealing temperature of 700 8C and at a hydrothermal growth temperature of 160 8C and growth time of 3 h. (a)
PT-substrate; (b) top view of TNAs; (c) side view of TNAs.
Fig. 6. Diameter distribution of TiO
2
nanorods grown on PT-substrate at an
annealing temperature of 700 8C and at a hydrothermal growth temperature of
160 8C and with growth time of 3 h.
Fig. 7. SEM image of TiO
2
nanorod arrays grown on the substrate at an annealing
temperature of 700 8C at a hydrothermal growth temperature of 190 8C and growth
time of 3 h.
Y. Li et al. / Materials Research Bulletin 44 (2009) 1232–1237
1235
that TiO
2
nanorods grow along the (1 1 0) crystal planes, and this is
consistent with the results of XRD.
Considering the effect of annealing temperature, the pre-coated
substrates were annealed at 450 and 600 8C, respectively. However,
after hydrothermal reaction, TiO

direction. However, as for the structure of anatase TiO
2
, all the TiO
6
octahedra connect through shared edges, which results in the same
growth velocity in all directions. It is the reason that the as-
prepared TiO
2
nanorods are rutile phase instead of anatase phase.
The formation of rutile crystal nucleus in TiCl
3
strongly acidic
precursor solution can be described by the following process [27].
First, single polymer [TiO(OH
2
)
5
]
2+
forms by the following reactive
equations:
Ti
3þ
þ 6H
2
O !½TiðOH
2
Þ
6


þ
þ O
2
þ 4H
þ
! 4½TiOðOH
2
Þ
5

2þ
þ 2H
2
O (3)
Then the single polymers [TiO(OH
2
)
5
]
2+
combine through
dehydrating each other to form straight chain polymer by the
edge connection. Finally, the straight chain polymers connect
through points to form rutile crystal nucleus.
As is well known, the heterogeneous nucleation of crystalline
phase in solution is easier than homogeneous nucleation [28].
Therefore, TiO
2
nanocrystal particles coated onto the glass
substrate followed by heat treatment can be served as the seeds

crystal growing along
[0 0 1] direction to form rod-like structure.
3.3. Photocatalytic property of TNAs
Fig. 10 shows photodegradation rate curves of TNAs grown on
different substrates and TiO
2
nanoparticles for methyl blue
Fig. 8. TEM images of TiO
2
nanorods grown on PT-substrate at an annealing
temperature of 700 8C and at a hydrothermal growth temperature of 160 8C and
with growth time of 3 h. (a) TEM image and the associated selected area electron
diffraction of TiO
2
nanorods; (b) lattice fringes image of high-resolution TEM of one
single TiO
2
nanorod at the side surface.
Fig. 9. FE-SEM image of the as-prepared TiO
2
arrays grown on PT-substrate when
NaCl is not added to the hydrothermal precursor solution at a hydrothermal growth
temperature of 160 8C and with growth time of 3 h.
Fig. 10. Photodegradation rate curves of TiO
2
nanoparticles (a) and TNAs grown on
different substrates for methyl blue solution: (b) PT-substrate without heat
treatment; (c) PT-substrate; (d) unmodified substrate. Hydrothermal growth
temperature: 160 8C and growth time: 3 h.
Y. Li et al. / Materials Research Bulletin 44 (2009) 1232–1237

boundary than that of single crystalline TNAs, which will make it
easier for the recombination of electron and hole pair. On the other
hand, TiO
2
nanoparticles may be agglomerated together and reduce
the surface area, while the distribution of the TNAs will protect it
from agglomeration. As a result, the photocatalytic activity greatly
improves with the prepared TNAs.
4. Conclusions
Large-scale, well-aligned TNAs were fabricated on the modified
glass substrate using hydrothermal approach. It has been
demonstrated that TNAs grown on PT-substrate have a better
growth orientation and uniform density compared with those
grown on the unmodified substrates. TiO
2
nanorod is a single
crystal rutile structure with growth direction along the (1 1 0)
crystal planes. About 67% of TiO
2
nanorods have a diameter
between 15 and 25 nm and the average diameter is about 21 nm,
and the length of TiO
2
nanorods ranges from 300 to 500 nm. In
addition, it indicates that TiO
2
nanoparticles coated on glass
substrate are not completely transformed into rutile phase after
heat treatment at 700 8C, and the (1 1 0) planes are the preferred
orientation. The photodegradation experiment implies that single

[12] M. Barbic, J.J. Mock, D.R. Smith, S. Schultz, J. Appl. Phys. 91 (2002) 9341.
[13] D. Xu, Y. Xu, D. Chen, G. Guo, L. Gui, Y. Tang, Chem. Phys. Lett. 325 (2000)
340.
[14] O.K. Varghese, D. Gong, M. Paulose, K.G. Ong, E.C. Dickey, C.A. Grimes, Adv. Mater.
15 (2003) 624.
[15] J.J. Wu, C.C. Yu, J. Phys. Chem. B 108 (2004) 3377.
[16] X.J. Feng, J. Zhai, L. Jiang, Angew. Chem. Int. Ed. 44 (2005) 5115.
[17] M. Guo, P. Diao, S.M. Cai, J. Solid State Chem. 178 (2005) 1864.
[18] T. Ma, M. Guo, M. Zhang, Y.J. Zhang, X.D. Wang, Nanotechnology 18 (2007)
035605.
[19] Y.H. Jiang, H.B. Yin, Y.M. Sun, H. Liu, L.X. Lei, K.M. Chen, Y.J. Wada, Appl. Surf. Sci.
253 (2007) 9277.
[20] M.N. Tahir, P. Theato, P. Oberle, G. Melnyk, S. Faiss, U. Kolb, A. Janshoff, M.
Stepputat, W. Tremel, Langmuir 22 (2006) 5209.
[21] K. Kakiuchi, E. Hosono, H. Imai, T. Kimura, S. Fujihara, J. Cryst. Growth 293 (2006)
541.
[22] J. Yang, S. Mei, J.M.F. Ferreira, P. Norby, S. Quaresma
ˆ
, J. Colloid Interf. Sci. 283
(2005) 102.
[23] X. Bokhimi, A. Morales, M. Aguilar, J.A. Toledo-Antonio, F. Pedraza, Int. J. Hydrogen
Energy 26 (2001) 1279.
[24] P. Hartman, W.G. Perdok, Acta Cryst. 8 (1955) 49.
[25] P. Hartman, W.G. Perdok, Acta Cryst. 8 (1955) 521.
[26] P. Hartman, W.G. Perdok, Acta Cryst. 8 (1955) 525.
[27] E.W. Shi, Z.Z. Chen, R.L. Yuan, Y.Q. Zheng, Hydrothermal Crystallography, Science
Press, Beijing, 2004, p. 150.
[28] L. Vayssieres, K. Keis, S.E. Lindquist, A. Hagfeldt, J. Phys. Chem. B 105 (2001) 3350.
Y. Li et al. / Materials Research Bulletin 44 (2009) 1232–1237
1237