Preparation of carbon–TiO
2
nanocomposites by a
hydrothermal method and their enhanced
photocatalytic activity
Guozhi Zhang,† Feng Teng,† Youqing Wang, Peng Zhang, Chengshi Gong,
Lulu Chen, Changhui Zhao and Erqing Xie
*
Carbon–TiO
2
nanocomposites were fabricated by a simple hydrothermal process, and the content of
carbon in the composites was adjusted by etching in air at high temperature. The synthesized
nanocomposites were characterized by SEM, TEM, XRD, Raman, UV-vis spectroscopy and PL
spectroscopy. The nanocomposites, with an average size of 50 nm, are composed of well-defined
crystallized TiO
2
with the amorphous carbon either on the surface or among particles. And the TiO
2
are
the mixed phase system of both anatase and rutile. Measurements of the photocatalytic degradation of
rhodamine B show that the photocatalytic activity of the carbon–TiO
2
nanocomposites, especially after
annealed at 400
C, is higher than that of pure TiO
2
. Experimental results indicate that the existence of
the carbon enhances the photocatalytic activity of C–TiO
2
nanocomposites via the synergistic effect
between carbon and TiO
2
, such as improving the adsorption, retarding the recombination of photo-
generated electron–hole pairs and absorbing more light.
Introduction
The photocatalytic properties of a semiconductor oxide are
derived from the formation of photo-generated charge carriers
(hole and electron), which occurs upon the absorption of
ultraviolet-visible (UV-vis) light corresponding to the band gap.
The photo-generated holes in the valence band diffuse to the
surface and react with adsorbed water molecules, forming
hydroxyl radicals (_OH). The photo-generated holes and the
hydroxyl radicals oxidize and decompose the organic molecule
around the photocatalyst. Meanwhile, photo-generated elec-
trons in the conduction band typically participate in the
reduction process, that they react with adsorbed molecular
oxygen to produce superoxide radical anions (O
2
).
1
Among all
the semiconductor oxides, titanium dioxide (TiO
2
) has been
intensively investigated in photocatalysis due to its relatively
low cost, high stability, non-toxicity, high photocatalytic effi-
ciency.
2–4
However, the applications of TiO
2
are greatly
restricted by its high recombination of photo-generated elec-
tron–hole pairs and wide band gap (3.2 eV for anatase).
5,6
In the
past decades, amounts of effective approaches have been
developed to increase the lifetime of photo-generated electron–
hole pairs and narrow the band gap, such as coupling with other
narrow band gap semiconductor materials,
7–10
modication
with metal and non-metal elements and structures,
11–15
hybridization with carbon materials,
16,17
noble metal deposition
or encapsulating noble metal core to form metal core@TiO
2
shell composites,
18–20
and surface sensitization by organic dye
molecules.
21–23
Although the absorption spectrum of TiO
2
is
broadened aer the bandgap narrowing, the recombination
rate of photo-generated carries becomes higher because
numerous recombination centres are produced, which result
from the i ntro duction of many impurities and defects for
narrowing the bandgap. Moreover, among t he various struc-
tures, nano sized TiO
2
particle shows great potential for high
photocatalytic activity and photoelectrical efficiencies
24
because of its huge surface area, which imply that many
defects e xist on the surface of TiO
2
nanoparticles. Theref ore,
in order to maximize the utilization of electron–hole pairs, the
photo-generated electrons should b e transferred off the TiO
2
because t he hole has the most direct e ffect i n the proces s of
organic degradation.
Among all candidate materials, carbon shows great advan-
tages. For example, carbon exhibits metallic conductivity as one
of the many possible electronic materials.
25
It has a large elec-
tron-storage capacity
26
and can accept the photon-excited elec-
trons to promote the separation of photo-generated carries.
Besides, it can sensitize TiO
2
by absorbing more visible light.
27,28
Carbon also can be used as a supporter for TiO
2
in the photo-
catalytic process.
29,30
Among all the allotrope of carbon, gra-
phene and carbon nanotubes are the two most commonly used
materials to suppress the recombination of electrons and holes
in the photocatalytic process. However, graphene (or CNT) can
School of Physical Science and Technology, Lanzhou Univers ity, Lanzhou 730000,
People's Republic of China. E-mail: xieeq@lzu.edu.cn; Fax: +86 9318913554; Tel:
+86 9318912616
† G. Z. Zhang and F. Teng contr ibuted equally to this work.
Cite this: RSC Adv., 2013, 3, 24644
Received 8th September 2013
Accepted 10th October 2013
DOI: 10.1039/c3ra44950e
www.rsc.org/advances
24644 | RSC Adv., 2013, 3, 24644–24649 This journal is ª The Royal Society of Chemistry 2013
RSC Advances
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