DSpace at VNU: Fabrication of photocatalytic composite of multi-walled carbon nanotubes TiO 2 and its application for desulfurization of diese

Materials Research Bulletin 47 (2012) 308–314

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Materials Research Bulletin
journal homepage: www.elsevier.com/locate/matresbu

Fabrication of photocatalytic composite of multi-walled carbon
nanotubes/TiO2 and its application for desulfurization of diesel
Thu Ha Thi Vu a,*, Thu Trang Thi Nguyen a, Phuong Hoa Thi Nguyen a, Manh Hung Do a,
Hang Thi Au a, Thanh Binh Nguyen b, Dinh Lam Nguyen c, Jun Seo Park d
a

Vietnam Institute of Industrial Chemistry, Hanoi, Viet Nam
Faculty of Chemistry, Hanoi University of Science, Vietnam National University, Hanoi, Viet Nam
Faculty of Chemical Engineering, Danang University of Technology, University of Danang, Viet Nam
d
Division of Chemical Engineering, Hankyong National University, Ansung 456-749, Republic of Korea
b
c

A R T I C L E I N F O

A B S T R A C T

Article history:
Received 25 May 2011
Received in revised form 24 September 2011
Accepted 9 November 2011
Available online 19 November 2011

Composite of multi-walled carbon nanotubes (MWNTs) and titanium (IV) oxide (TiO2) were prepared by
a heterogeneous gelation method. The activities of the MWNTs/TiO2 composites were evaluated by
photocatalytic oxidative desulfurization using dibenzothiophene (DBT), 4,6-dimethyl dibenzothiophene
(4,6-DMDBT), n-tetradecane, and commercial diesel under irradiation using a high-pressure Hg lamp.
The microstructures of MWNTs/TiO2 composites were characterized by N2 adsorption, scanning electron
microscopy, transmission electron microscope, and X-ray diffraction. It was found that more than 98% of
sulfur compounds in commercial diesel were oxidized and removed by the use of the MWNTs/TiO2
composite as a photocatalyst.
ß 2011 Elsevier Ltd. All rights reserved.

Keywords:
Desulfurization
Composite
Multi-walled carbon nanotubes
TiO2

1. Introduction
In the fuel combustion process, sulfur compounds in the fuel are
transformed into SOx causing air pollution and acidic rain. To
reduce the negative effects on human health and the environment,
the reduction of the sulfur content in fuel has been investigated.
Desulfurization by hydrogen (HDS) in the presence of a catalyst has
been commonly employed to reduce the sulfur content in fuel [1].
However, it is difficult to use this method for deep desulfurization
(<50 ppm), because dibenzothiophene (DBT) and its derivatives,
such as 4,6-dimethyl dibenzothiophene (4,6-DMDBT), are strongly
stable to hydrogenation [2]. Hence, DBT and (4,6-DMDBT) have
been commonly used as model compounds for the investigation of
desulfurization.
To reduce the sulfur content in fuel, semiconductor photocatalysts have attracted much recent attention. TiO2 has been

widely studied as a semiconductor photocatalyst to oxidate DBT
and its derivatives in diesel into sulfone and sulfoxide which is
easier to remove using adsorption by silicagel [3–5]. Besides TiO2,
semi-conductors such as ZnO [6], CdS and GaP [7] have also been
employed as photocatalysts. These substances can absorb more
solar energy than TiO2, but they are easily disintegrated during the

* Corresponding author. Tel.: +84 422189067; fax: +84 439335410.
E-mail address: (T.H.T. Vu).
0025-5408/$ – see front matter ß 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.materresbull.2011.11.016

photocatalytic process. Anatase TiO2 has been used as a photocatalyst because of its high photocatalytic activity, chemical
stability, non-toxicity, physical properties and low cost [8,9].
However, TiO2 powder has some drawback such as lower interface
and easy recombination of the electron–hole pair [9,10]. To
overcome this shortcoming of TiO2, many researchers have sought
to improve the photocatalytic activity of TiO2 under visible light.
There has been considerable progress in the production of new
functional materials by coupling TiO2 with other organic or
inorganic material [10]. One of the most commonly used methods
for improving the photocatalytic activity is the combination of
MWNTs with TiO2 [11–14].
Carbon multiwall nanotubes (MWNTs) have been extensively
studied because they have many useful properties such as good
electrical conductivity, nanosize absolute black, excellent mechanical properties, large surface area, and high adsorption capacity
[12,15,16]. In addition, MWNTs have a large electricity-storage
capacity, and therefore, it may accept photon-excited electrons in
mixtures or nanocomposites with titania, thus retarding or
hindering recombination [12]. Hence, the combination of MWNTs

with TiO2 can reduce charge recombination, enhance reactivity
and enhance photocatalytic ability of TiO2 [10,17,18].
MWNTs/TiO2 composites not only retain the characteristics of
each component, but also exhibit high photo-chemical activity
[18–20]. The rate of photo-catalytic oxidation of DBT and its
derivative was increased using MWNTs/TiO2 [3,21]. These


T.H.T. Vu et al. / Materials Research Bulletin 47 (2012) 308–314

composite materials have been fabricated by various methods such
as the sol–gel method [11,13], electro-spinning [17,22], electrophoretic deposition [22], and chemical vapor deposition (CVD)
[23]. The uniformity of the MWNTs coating and the physical
properties of the composite materials vary according to the
fabrication method [12]. Uniform coating of MWNTs on TiO2 can be
achieved by employing CVD and electrospinning [22,23]; however,
these techniques are not simple and require specialized equipment
[12].
In this study, MWNTs were prepared by employing CVD
method because its procedure is simple. The composite was then
formed by homogeneous granulation by realingzing the heterogeneous gelation of the MWNTs and TiO2. The microstructure of the
MWNTs/TiO2 composites was characterized by N2 adsorption,
scanning electron microscopy, transmission electron microscope,
and X-ray diffraction. Photoluminescence spectroscopy was
employed to study the effects of MWNTs on the photocatalytic
activity of MWNTs/TiO2 composites. The photocatalytic activity
was evaluated by the photocatalytic reaction of DBT and 4,6DMDBT in the presence of TiO2 and the MWNTs/TiO2 composite.
Deep desulfurization of diesel was carried out by two consecutive
processes involving the photo-oxidation of the sulfur compound to
sulfone and sulfoxide which are easier to adsorb, followed by the

adsorption of these compounds by silicagel. The effect of photooxidation and adsorption using MWNTs/TiO2 as the photocatalyst
for the desulfurization of diesel was also investigated.
2. Experimental
2.1. Material
Commercial titanium oxide (99.4% about 130 nm, ROHA
Dyechem Vietnam Co., Ltd., Vietnam) was used without further
treatment. Carbon source and CaCl2 were purchased from Sigma
Aldrich (USA).
2.2. Fabrication of MWNTs and MWNTs/TiO2 composite catalyst
MWNTs was fabricated by the CVD method using Fe/g-Al2O3 as
the catalyst and LPG as the feedstock at 690–710 8C [23]. In center
of a gypsum calciner, 0.2 g of Fe/g-Al2O3 was placed, and LPG was
bellowed into the calciner. The reaction temperature and reaction
time were around 690–710 8C and 2 h, respectively.
The MWNTs/TiO2 composite photocatalyst was prepared as
follows: 0.4 g of sodium alginate was slowly added to 60 ml of
distilled water with stirring to form a homogeneous solution.
MWNTs and TiO2 were dispersed in the solution with different
MWNTs:TiO2 mass ratios of 1:20, 1:10, and 1:3 using an
ultrasonifier (VC 505/VC 750). The catalyst was granulated in
0.5 M CaCl2 solution. The catalyst particles were carefully washed
and then dried at 80 8C for 5 h. The final product was obtained after
calcining at 400 8C in air for 5 h.
2.3. Characterization of the catalyst
The morphology of the MWNTs/TiO2 composites was observed
by SEM using an S-4800 microscope (Hitachi, Japan).
Transmission electron microscopy was performed on a Leica
LEO 906E instrument operating at 120 kV. The samples were first
dispersed in ethanol.
X-ray diffraction (XRD) was determined over the 2u range 10–

808 (D8 ADVANCE, Bruker, Germany) using copper radiation Cu
Ka1 (l = 0.16 A˚) as the X-ray source.
The Brunauer–Emett–Teller (BET) surface area of the MWNTs
was evaluated from the N2 adsorption isotherm at 77 K using a BET
Sorptometer. (Automated Sorptometer BET 201-A, USA).

309

The photoluminescence spectra of MWNTs/TiO2 composites
were obtained using a fluorescence spectrophotometer iHR550
(Jobin-Yvon, French).
2.4. Photo-oxidation of MWNTs/TiO2 composites with DBT and 4,6DMDBT
Evaluation of the photocatalytic activity of the MWNTs/TiO2
composite by the photo-oxidation of DBT and 4,6-DMDBT was
carried out in with the solid catalyst suspended in solution. The
reactor system consisted of a high-pressure mercury lamp, a
500 ml volume glass reactor containing the reaction solution, a
magnetic stirrer, and a reflective mirror system. The beaker was
placed in the middle of the system to focus the maximum amount
of light to the reaction solution.
Evaluation of photo-catalytic activity of MWNTs/TiO2 composite (mass ratio 1:20) included the following steps: DBT or 4,6DMDBT was dissolved in n-tetradecane. The sulfur content in the
reaction solution was 200 ppm. The total content of sulfur was
determined using a TS-100V (Mitsubishi, Japan) according to ASTM
D5453-06. An amount of 100 ml of the reaction solution was
poured into a glass reactor and 1 g of photo-catalyst was added.
The mixed solution was then placed in the dark for at least 2 h to
establish an adsorption–desorption equilibrium, which is hereafter
considered to be the initial concentration after dark adsorption.
The reactor was then inserted into the above photo-catalytic
reaction system. The photo-catalytic reaction was initiated by

irradiation with a high pressure Hg lamp while stirring. As a result
of the photo-catalytic reaction the sulfur compound was changed
into sulfone and sulfoxide which is easier to adsorb. Then the
sulfone and sulfoxide in the solution were absorbed by silica gel.
The products formed after adsorption were determined by
elemental analysis according to the ASTM D5453-06 method.
2.5. Desulfurization of commercial diesel
Commercial diesel, whose total sulfur content is 714 ppm, was
added 1 g photocatalysis and placed in the dark for at least 2 h to
establish an adsorption–desorption equilibrium. This solution was
then pretreated to remove colored and sulfur compounds in order
to lower the sulfoxide and sulfone contents. The diesel was
subsequently treated with the MWNTs/TiO2 photocatalyst (mass
ratio, 1:20) (with a concentration of 1 g of catalyst/100 ml of
diesel) and irradiated with the high-pressure Hg lamp (OSRAM
250W, Germany). The samples were periodically taken out every
20 min and centrifuged to remove solid catalyst. The sulfur
compound in the diesel was changed into sulfone and sulfoxide.
The sulfone and sulfoxide were absorbed by silica gel and its
content of sulfur was determined by X-ray fluorescence (XRF) (TS100V, Mitsubishi, Japan).
3. Results and discussion
3.1. Morphology of MWNTs and MWNTs/TiO2 composite
photocatalyst
The BET surface area of TiO2, MWNTs and MWNTs/TiO2
composites prepared from MWNTs and TiO2 with different
MWNTs/TiO2 mass ratios are shown in Table 1. The surface area
of TiO2 and MWNTs are 8.44 m2/g and 152.48 m2/g, respectively.
The BET surface area of MWNTs/TiO2 composites were 17.32 m2/g,
34.23 m2/g, and 38.34 m2/g for MWNTs/TiO2 mass ratios of 1:20,
1:10, and 1:3, respectively. It is observed from Table 1 that there is

a significant change in the micropore size of the MWNTs/TiO2
catalyst composites compare to that of the corresponding bare
TiO2, and the surface area of MWNTs/TiO2 composites increased


310

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Table 1
BET surface area (SBET) of the MWNTs/TiO2 composites.
Samples

SBET (m2/g)

TiO2
(1:20) MWNTs/TiO2
(1:10) MWNTs/TiO2
(1:3) MWNTs/TiO2
MWNTs

8.44
17.32
34.23
38.34
152.48

with increasing MWNTs content in the composites. This can be
explained by the fact that MWNTs have a high surface area and the
combination of MWNTs with TiO2 can increase the surface area of

TiO2 in the composites. This suggests that MWNTs has a significant
effect on the adsorption ability of TiO2.
Fig. 1 shows SEM micrographs of MWNTs/TiO2 composites with
different MWNTs/TiO2 mass ratios. Fig. 1(e) shows that the average
diameter of nano-carbon tubes is around 14 nm. This result

corresponds to the value of the high specific surface area of MWNTs
obtained using the BET method. In Fig. 1(b) at a mass ratio of 1:20,
few MWNTs were evident, but those that were visible were
interwoven among the TiO2 particles. At a 1:10 mass ratio, the
MWNTs were in contact with one another and interwoven among
the TiO2 particles (as shown in Fig. 1(c)). At a 1:3 mass ratio (Fig. 1(d)),
the MWNTs were well dispersed, and draping over and nearly
covering some of the TiO2 particles. It was found that the MWNTs
were uniformly distributed, which resulted in anatase crystallites.
Fig. 1 indicates that the MWNTs and TiO2 were mixed well, forming
uniform microstructures in the MWNTs/TiO2 composites.
Fig. 2 shows TEM micrographs of MWNTs/TiO2 composites with
different MWNTs/TiO2 mass ratios. It was found that few MWNTs
cover the TiO2 particles in MWNTs/TiO2 composites with mass
ratios of MWNTs/TiO2 of 1:20 (as shown in Fig. 2(b)). When the
content of MWNTs in the MWNTs/TiO2 composites increased and
the mass ratios became 1:10 and 1:3, the MWNTs came in contact
with one another and embedded the TiO2 particles (as shown in

Fig. 1. SEM micrographs of the MWNTs/TiO2 composites with different MWNTs/TiO2 mass ratios: (a) TiO2, (b) MWNTs/TiO2: 1:20, (c) MWNTs/TiO2: 1:10, (d) MWNTs/TiO2:
1:3, and (e) MWNTs.


T.H.T. Vu et al. / Materials Research Bulletin 47 (2012) 308–314

311

Fig. 2. TEM micrographs of the MWNTs/TiO2 composites with different MWNTs/TiO2 mass ratios; (a) TiO2, (b) MWNTs/TiO2: 1:20, (c) MWNTs/TiO2: 1/10, (d) MWNTs/TiO2: 1/
3, and (e) MWNTs.

Fig. 2(c) and (d), respectively). When the MWNTs/TiO2 composites
had mass ratios of 1:3, the MWNTs were uniformly dispersed and
covered all the TiO2 particles. This indicates again that MWNTs
were well dispersed on the surface of the TiO2 particles and that
the MWNTs and TiO2 particles were in close contact with each
other.
3.2. XRD analysis
XRD patterns of the MWNTs, TiO2 and the MWNTs/TiO2
composite after calcining at 400 8C for 5 h are shown in Fig. 3. A

characteristic peak of the MWNTs corresponding to the 258
reflection planes is identified (shown in Fig. 3(a)) [2,24]. It was
reported that the anatase phase of TiO2, which was formed at
temperatures less than 500 8C, started changing into the rutile
phase at 600 8C and was completely changed to the rutile form at
900 8C [25]. In this sample, only the anatase phase was identified in
theTiO2 and MWNTs/TiO2 composite. The reflection at around
2u = 48.18 was attributed to the crystalloid form of anatase TiO2,
where there was no interference from MWNTs. From the
comparison of spectra between Fig. 3(b) and (c), the structure of
TiO2 in the MWNTs/TiO2 catalyst is almost the same. This indicates


T.H.T. Vu et al. / Materials Research Bulletin 47 (2012) 308–314

312

TiO2
MWNTs

(c)

(b)

Fig. 4. Photoluminescence spectra of the MWNTs/TiO2 composites with different
MWNTs/TiO2 mass ratios: (a) TiO2, (b) (1:20) MWNTs/TiO2, (c) (1:10) MWNTs/TiO2,
(d) (1:3) MWNTs/TiO2, and (e) MWNTs.

(a)

5

10

20

30

40

50

60

70

80

2-Theta - Scale
Fig. 3. XRD patterns of (a) MWNTs, (b) TiO2, and (c) (1:20) MWNTs/TiO2 composite.

that there is no difference in the microstructure of TiO2 before and
after combination with MWNTs.
3.3. Photoluminescence spectra
Photocatalytic activity is, in part, a function of the life-time and
trapping of electrons and holes. Photoluminescence is often
employed to investigate surface structure and excited states and
to follow surface processes involving the electron/hole fate of TiO2
[8,10]. When electron/hole pair recombination occurs after a
photocatalyst has been irradiated (i.e., laser), photons are emitted,
resulting in photoluminescence. This behavior is attributed to the
reverse radiative deactivation from the excited-state of the Ti [10].
The photoluminescence intensity of material is decrease the
charge recombination of electron/hole is increase. Fig. 4 shows the
photoluminescence spectra of the MWNTs/TiO2 composite with
various MWNTs/TiO2 mass ratios. The photoluminescence spectrum for anatase TiO2 shows a characteristic by a broad peak at
around 475 nm, whereas no luminescence of MWNTs is observed

in the range of 450–650 nm. The photoluminescence intensities of
the MWNTs/TiO2 composites with various mass ratios were lower
than that of TiO2 indicating reduced charge recombination of
MWNTs/TiO2 composites in comparison to TiO2 anatase alone. In
other words, the combination of MWNTs and TiO2 contribute to
improving photocatalytic activity of TiO2.

Two mechanisms have been proposed to explain the enhancement of photocatalytic activity of the MWNTs/TiO2 composite
which is due to the decreased charge recombination of excited
electrons and holes, and the efficient electron transport by
MWNTs. The first mechanism was proposed by Martin et al.
[26]. Under UV illumination, electrons (eÀ) are excited from the
valence band (VB) to the conduction band (CB) of the anatase,
creating a charge vacancy, or hole (h+) in the VB. In the absence of
the MWNTs, most of these charges recombine quickly without
doing any chemistry. Typically, only a small number of electrons
and holes are trapped and these trapped electros and holes
participate in photocatalytic reactions, resulting in low reactivity.
Hence, when a high energy photon is absorbed by titanium oxide, it
will stimulate an electron of the photocatalyst to transfer from the
valence band to the conduction band. These electrons are absorbed
by the MWNTs, and the holes of TiO2 participate in redox reactions.
A diagram of the mechanism is shown in Fig. 5(a) [15,26]. The
second mechanism was proposed by Wang et al. [27]. When
MWNTs absorb photons, they are considered as sensitive
substances. MWNTs release electrons and then these electrons
are transferred into the conduction band of TiO2, which are
absorbed by oxygen molecules forming strong oxidant radicals.

Fig. 5. Mechanism of the enhancement of photocatalytic activity of the composite MWNTs/TiO2 proposed by (a) Martin et al. [26], and (b) Wang et al. [27].


T.H.T. Vu et al. / Materials Research Bulletin 47 (2012) 308–314

313

Fig. 6. Adsorbability of TiO2, MWNTs/TiO2 composites (mass ratios 1:20) for DBT,

4,6-DMDBT and diesel under dark condition.

When this process occurs, a positive charge on the MWNTs, which
is created when electrons move to the conduction band of TiO2,
removes one of the valence electrons of TiO2 and leaves a hole on
the TiO2. This hole is positively charged, and it can react with
adsorbed water molecules to create hydroxyl radicals (OH). This is
illustrated in Fig. 5(b) [15,27].
3.4. Adsorption ability
The adsorption ability of TiO2 and MWNTs/TiO2 composite
(mass ratio = 1:20) on DBT, 4,6-DMDBT and sulfur compound in
diesel under dark condition are shown in Fig. 6. It was found that
the absorption ability of TiO2 and MWNTs/TiO2 composite is very
low. The level of DBT, 4,6-DMDBT and diesel absorption by
MWNTs/TiO2 composite is slightly higher than that of the TiO2.
This behavior can be explained that the surface area of the MWNTs/
TiO2 composite (mass ratios 1:20) (17.32 m2/g) is slight larger than
that of TiO2 (8.44 m2/g) (as shown in BET results). In addition, the
enhanced adsorption ability can be related to the amount of
MWNTs in the MWNTs/TiO2 composite [9]. Hence, there is not
much difference in adsorption ability between the MWNTs/TiO2
composite (mass ratios 1:20) and TiO2.

Fig. 7. Comparison between the photo-activity of TiO2 and that of (1:20) MWNTs/
TiO2 in the photo-oxidation reaction of (a) DBT, and (b) 4,6-DMDBT.

3.5. Photocatalytic activity of desulfurization of DBT and 4,6-DMDBT
The conversion of DBT and 4,6-DMDBT using TiO2 and the
MWNTs/TiO2 composite photocatalysts (mass ratio = 1:20) are
shown in Fig. 7. The results show that the photocatalytic activity

of MWNTs/TiO2 is higher than that of commercial TiO2 in the photooxidation of both DBT and 4,6-DMDBT. This indicates that MWNTs
enhance the photocatalytic activity or there was a synergistic effect
between the photocatalytic activities of TiO2 and MWNTs in the
photo-oxidation reaction of DBT and 4,6-DMDBT. The photoluminescence spectra given in Fig. 4 also demonstrate the enhancement
of the photocatalytic activity of TiO2 by using MWNTs.

composite for 120 min, most of the sulfur compounds were
oxidized to sulfone and sulfoxide, which could be easily absorbed
by silica gel. This result indicates that there was a synergistic effect
between the TiO2 and MWNTs in the MWNTs/TiO2 composite
during the photocatalysis of sulfur compounds in diesel.

3.6. Photocatalytic activity of desulfurization of diesel
The relationship between the sulfur content in diesel and
reaction time using TiO2 and the MWNTs/TiO2 composite
photocatalyst (mass ratio = 1:20) is shown in Fig. 8. The result
shows that the rate of photocatalysis by using commercial TiO2
was significantly lower than that of photocatalysis by using
MWNTs/TiO2 composite. After treating with the MWNTs/TiO2
composite for 120 min followed by absorption with silica-gel, the
sulfur content in the diesel was approximately 0 ppm. On the other
hand, when the diesel was treated with commercial TiO2 under the
same conditions, the sulfur content was around 400 ppm. The
reason for this is that after treating with the MWNTs/TiO2

Fig. 8. Relation between sulfur content and reaction time.


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T.H.T. Vu et al. / Materials Research Bulletin 47 (2012) 308–314

4. Conclusions
A photo-catalytic MWNTs/TiO2 composite was successfully
fabricated by the heterogeneous gelation method. MWNTs and
TiO2 were mixed to form MWNTs/TiO2 composites with a uniform
microstructure. The microstructure of TiO2 before combination
with MWNTs is similar with that of TiO2 after combination with
MWNTs. The addition of MWNTs to the composites improved the
photocatalysis of TiO2. The MWNTs/TiO2 composite was evaluated
on the basis of the oxidation of model compounds such as DBT and
4,6-DMDBT with heterocyclic sulfur compounds in diesel. Most of
the sulfur in diesel was removed after 120 min of photocatalytic
reaction using the MWNTs/TiO2 composite, followed by adsorption. This success is attributed to the synergistic effect of TiO2 and
MWNTs in the MWNTs/TiO2 composite during the photo-catalytic
reaction. The MWNTs/TiO2 composite is an effective photocatalyst for the removal of sulfur from commercial diesel.
Acknowledgement
This project was carried out within the framework of the basic
topics in 2009–2011 and was funded by the National Foundation
for Science and Technology Development.
References
[1] T.V. Rao, P.M. Krishna, D. Paul, B.R. Nautiyal, J. Kumar, Y.K. Sharma, S.M. Nanoti, B.
Sain, M.O. Garg, Petrol. Sci. Technol. 29 (2011) 626–632.
[2] C.G. Silva, J.L. Faria, Appl. Catal. B: Environ. 101 (2010) 81–89.

[3] J. Robertson, T.J. Bandosz, J. Colloid Interface Sci. 299 (2006) 125–135.
[4] J.T.S. Matsuzawa, S. Dato, T. Ibusuki, J. Photochem. Photobiol. A: Chem. 149 (2002)
183–189.
[5] D. Zhao, J. Zhang, J. Wang, W. Liang, H. Li, Petrol. Sci. Technol. 27 (2009) 1–11.
[6] J. Rabani, J. Phys. Chem. 93 (1989) 7707–7713.

[7] T.S.I. Honma, H. Komiyama, J. Phys. Chem. 97 (1993) 6692–6695.
[8] K. Fujihara, S. Izumi, T. Ohno, M. Matsumura, J. Photochem. Photobiol. A: Chem.
132 (2000) 99–104.
[9] K. Zhang, F.J. Zhang, M.L. Chen, W.C. Oh, Ultrason. Sonochem. 18 (2011) 765–772.
[10] Y. Yao, G. Li, S. Ciston, R.M. Lueptow, K.A. Gray, Environ. Sci. Technol. 42 (2008)
4952–4957.
[11] T.C.A. Jitianu, M. Berger, R. Benoit, F. Be´guin, S. Bonnamy, J. Non-Cryst. Solids 345–
346 (2004) 596–600.
[12] M.L. Chen, F.J. Zhang, W.C. Oh, New Carbon Mater. 24 (2009) 159–166.
[13] W.D. Wang, P. Serp, P. Kalck, J.L. Faria, Appl. Catal. B: Environ. 56 (2005) 305–312.
[14] H. Yu, X. Quan, S. Chen, H. Zhao, J. Phys. Chem. C 111 (2007) 12987–12991.
[15] K. Woan, G. Pyrgiotakis, W. Sigmund, Adv. Mater. 21 (2009) 2233–2239.
[16] X. Gui, J. Wei, K. Wang, A. Cao, H. Zhu, Y. Jia, Q. Shu, D. Wu, Adv. Mater. 22 (2010)
617–621.
[17] S. Aryal, C.K. Kim, K.-W. Kim, M.S. Khil, H.Y. Kim, Mater. Sci. Eng. C 28 (2008) 75–
79.
[18] A. Jitianu, T. Cacciaguerra, R. Benoit, S. Delpeux, F. Be´guin, S. Bonnamy, Carbon 42
(2004) 1147–1151.
[19] Y. Yu, J.C. Yu, C.-Y. Chan, Y.-K. Che, J.-C. Zhao, L. Ding, W.-K. Ge, P.-K. Wong, Appl.
Catal. B: Environ. 61 (2005) 1–11.
[20] W. Fan, L. Gao, J. Sun, J. Am. Ceram. Soc. 89 (2006) 731–733.
[21] R. Vargas, O. Nu´n˜ez, J. Mol. Catal. A: Chem. 294 (2008) 74–81.
[22] J. Cho, S. Schaab, J. Roether, A. Boccaccini, J. Nanopart. Res. 10 (2008) 99–105.
[23] M. Corrias, B. Caussat, A. Ayral, J. Durand, Y. Kihn, P. Kalck, P. Serp, Chem. Eng. Sci.
58 (2003) 4475–4482.
[24] W. Zhou, K. Pan, Y. Qu, F. Sun, C. Tian, Z. Ren, G. Tian, H. Fu, Chemosphere 81 (2010)
555–561.
[25] S. Yang, W. Tang, Y. Ishikawa, Q. Feng, Mater. Res. Bull. 46 (2011) 531–537.
[26] S.T. Martin, M.R. Hoffmann, W. Choi, D.W. Bahnemannt, Chem. Rev. 95 (1995) 69–
96.

[27] P.S.W.D. Wang, P. Kalck, J.L. Faria, J. Mol. Catal. A: Chem. 235 (2005) 194.