Dramatic visible light photocatalytic activity of MnOx-BiOI heterogeneous photocatalysts and the selectivity of the cocatalyst

Article abstract of DOI:10.1039/c3ta11441d

Charge separation is very important for increasing the activity of semiconductor-based photocatalysts. Here we show that the main active species of BiOI are photo-induced holes, rather than OH and O₂^-, under visible light irradiation. Based on this finding, the cocatalyst MnO _x was used to enhance the transfer of the photo-induced holes, resulting in much higher photocatalytic activity, compared with the photocatalyst without MnO_x. MnO_x-BiOI heterogeneous nanostructure photocatalysts have been prepared by photo-deposition in Mn(NO₃)₂ solution, and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and photoluminescence (PL) spectroscopy. As-prepared MnO_x-BiOI exhibited higher photoactivity than BiOI and Pt-BiOI for the degradation of Rhodamine B (RhB) dye under visible light irradiation. The PL spectrum showed that MnO _x enhances the separation efficiency of the photo-induced electrons and holes of BiOI. Finally, BiOI was selectively combined with a deriving-hole-type cocatalyst to enhance the photocatalytic activity, and the reason for the cocatalyst selectivity is also discussed. This finding may be useful in bismuth-based photocatalysts to construct highly efficient solar energy conversion systems.

Full text of DOI:10.1039/c3ta11441d

Journal of
Materials Chemistry A
View Article Online
View Journal | View Issue
PAPER
Dramatic visible light photocatalytic activity of
MnOx–BiOI heterogeneous photocatalysts and the
Cite this: J. Mater. Chem. A, 2013, 1,
8978
selectivity of the cocatalyst
a
a
a
a
b
*
*
Liqun Ye, Xiaodi Liu, Qiang Zhao, Haiquan Xie and Ling Zan
Charge separation is very important for increasing the activity of semiconductor-based photocatalysts. Here
we show that the main active species of BiOI are photo-induced holes, rather than_OH and O2_ꢀ, under visible
light irradiation. Based on this finding, the cocatalyst MnOx was used to enhance the transfer of the photo-
induced holes, resulting in much higher photocatalytic activity, compared with the photocatalyst without
MnOx. MnOx–BiOI heterogeneous nanostructure photocatalysts have been prepared by photo-deposition
in Mn(NO3)2 solution, and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy
(XPS), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM)
and photoluminescence (PL) spectroscopy. As-prepared MnOx–BiOI exhibited higher photoactivity than
BiOI and Pt–BiOI for the degradation of Rhodamine B (RhB) dye under visible light irradiation. The PL
spectrum showed that MnOx enhances the separation efficiency of the photo-induced electrons and
holes of BiOI. Finally, BiOI was selectively combined with a deriving-hole-type cocatalyst to enhance the
photocatalytic activity, and the reason for the cocatalyst selectivity is also discussed. This finding may be
useful in bismuth-based photocatalysts to construct highly efficient solar energy conversion systems.
Received 10th April 2013
Accepted 31st May 2013
DOI: 10.1039/c3ta11441d
www.rsc.org/MaterialsA
high recombination efficiency of photo-induced electrons and
holes. Therefore, cocatalysts are needed to enhance the sepa-
1 Introduction
Semiconductor photocatalysis is a very effective and green
technique for the elimination of most kinds of environmental
pollutants.1 The study of visible light-driven (VLD) photo-
catalysts has been undertaken by an increasing number of
researchers.2 Recently, BiOX (X ¼ Cl, Br, I) were reported as
efficient photocatalysts.3–11 BiOX have an indirect-transition
band-gap and a layered structure. The indirect-transition band-
gap of BiOX results in the excited electron having to travel a
certain k-space distance to be emitted to the valence band (VB),
which reduces the recombination probability of the excited
electron and the hole.12–14 On the other hand, the layered
structure provides a large enough space to polarize the related
atoms and orbitals, and then induce the presence of internal
static electric elds perpendicular to the [Bi2O2] slabs and the
halogen anionic slabs in BiOX.12–14 Finally, the effective sepa-
ration of the photoinduced electron–hole pairs along the [001]
direction is displayed. Because of this, BiOX display high pho-
tocatalytic activity.1–21
ration efficiency of the photo-induced electrons and holes of
BiOI, and then increase their VLD photocatalytic activity.22,23
Cocatalysts usually can be divided into deriving-electron-
types (Ag, Pt, Au) and deriving-hole-types (PbO2, MnOx).24 It has
been reported that a Pt cocatalyst can enhance the separation
efficiency of the photoinduced carriers of BiOI, and then
increase the VLD photocatalytic activity.22 However, to our best
knowledge, there are no reports about deriving-hole-type
cocatalyst depositing on BiOI. Additionally, it must be pointed
out that photo-induced holes are the main active species of
many bismuth-based photocatalysts for dye degradation. So,
deriving-hole-type cocatalysts may be more effective in
enhancing the separation efficiency of the photoinduced
carriers of BiOI.
In this paper, MnOx–BiOI heterogeneous nanostructure
photocatalysts have been prepared by photo-deposition and
used to study the selectivity of the cocatalyst. The photocatalytic
degradation (PCD) results showed that MnOx–BiOI exhibited
higher VLD photocatalytic activity than BiOI and Pt–BiOI. The
origin of the cocatalyst selectivity was also discussed.
Among the BiOX photocatalysts, BiOI shows the smallest
band-gap (1.8 eV) which results in more absorption of visible
light. On the other hand, the small band-gap also results in the
2 Materials and methods
2.1 Materials and preparation
aCollege of Chemistry and Pharmaceutical Engineering, Nanyang Normal University,
Nanyang 473061, People's Republic of China. E-mail: yeliquny@163.com
bCollege of Chemistry and Molecular Science, Wuhan University, Wuhan 430072,
People's Republic of China. E-mail: irlab@whu.edu.cn
BiI3 was analytically pure and bought from Aladdin Chemistry
Co., Ltd. Mn(NO3)2, H2PtCl6 and ethanol were analytically pure
8978 | J. Mater. Chem. A, 2013, 1, 8978–8983
This journal is ª The Royal Society of Chemistry 2013

View Article Online
Paper
Journal of Materials Chemistry A
and from Sinopharm Chemical Reagent Co., Ltd. Rhodamine B UV-visible spectra of the dye using a Shimadzu UV-3600
(RhB) wasanalytically pure andused without further purication. spectrophotometer.
BiOI without cocatalyst was synthesized according to ref. 25.
0.5 g BiI3 was added into a ceramic crucible for calcination.
2.4 Photoactivity mechanism
The annealing process was performed in air with a heating rate
For detecting the active species during the photocatalytic reac-
tion, hydroxyl radicals (_OH), superoxide radicals (O2_ꢀ) and
holes (h+) were investigated by adding 1.0 mM IPA (a quencher
of _OH), BQ (a quencher of O2_ꢀ) and TEOA (a quencher of h+),
respectively.26–32 The method is similar to the former photo-
catalytic activity test.
of 5 C minꢀ1, which was followed by cooling at room temper-
ꢁ
ature. Aer, the product was thoroughly washed with ethanol
ꢁ
and deionized water, and dried at 80 C.
MnOx–BiOI heterogeneous photocatalysts were synthesized
by photo-deposition. 0.5 g BiI3 powder and a calculated amount
of metal precursors (1 mol%) were mixed in 100 mL deionised
water. The suspension was then irradiated by a 500 W Xe lamp
under continuous stirring at 90 ꢁC. Aer 3 h photo-deposition,
the suspension was ltered, washed withꢁdeionised water more
than three times, and nally dried at 80 C.
Nitro blue tetrazolium (NBT) (2.5 ꢂ 10ꢀ5 mol Lꢀ1, exhibiting
an absorption maximum at 259 nm) was used to determine the
amount of O2_ꢀ generated by the BiOI photocatalytic system.
The production of O2_ꢀ was quantitatively analyzed by detecting
the concentration of NBT with a Shimadzu UV-3600 spectro-
photometer. The method is similar to the former photocatalytic
activity test, with NBT replacing RhB. O2_ꢀ production under
different monochromatic light wavelengths of 400 and 550 nm
was measured.26,27
For comparison, the simultaneous photo-deposition of Pt
(1 mol%) was synthesized according to ref. 22.
2.2 Characterization
X-ray diffraction (XRD) patterns of the samples were recorded at
room temperature, by a Bruker D8 advance X-ray diffractometer
using Cu Ka radiation and a 2q scan rate of 6ꢁ minꢀ1. The
diffraction patterns were recorded over the 2q range 8–60ꢁ. The
Brunauer–Emmett–Teller (BET) surface areas were collected
using quantachrome autosorb-1 automated gas sorption
systems at 77 K. TEM images were obtained by a JEM-2100 (HT)
transmission electron microscope operating at an accelerating
voltage of 200 kV. HRTEM images and fast-Fourier transform
(FFT) patterns were obtained by a JEOL JEM-2010FEF eld
emission electron microscope operating at an accelerating
voltage of 200 kV. X-ray photoelectron spectroscopy (XPS)
measurements were carried out by a VG Multilab 2000 spec-
trometer (Thermo Electron Corporation), with an Ar Ka X-ray
source and the spectra calibrated to the C 1s peak at 284.6 eV.
Photoluminescence (PL) spectra of BiOI powder was obtained
on a Jasco FP-6500 with lexc ¼ 400 nm.
3 Results and discussion
3.1 Characterization of MnOx–BiOI
Fig. 1 shows the XRD patterns of irregular BiOI and MnOx–BiOI.
All of the XRD peaks of BiOI can be indexed to tetrahedral BiOI
(JCPDS no. 00-073-2062), and no residual Bi, BiI3, Bi2O3 or
Bi5O7I phases were detected. This indicates that the BiOI
sample is pure BiOI. Additionally, it can be seen that the (001)
peak of BiOI is much higher than the (110) peak. It implies that
the BiOI has exposed {001} facets.25 Aer the photo-deposition
of MnOx, MnOx–BiOI showed the same pattern and I001/I110
ratio. This indicates that the modication of BiOI by MnOx did
not alter the lattice structure and the exposed {001} facet
percentage of BiOI.
Fig. 2 shows the high-resolution XPS spectra of the MnOx–
BiOI heterogeneous nanostructures compared to those of pure
BiOI. As shown in Fig. 2a, the two peaks of the Bi region at 159.1
and 164.5 eV are assigned to Bi 4f7/2 and Bi 4f5/2 respectively.
The two peaks located at 618.9 and 630.4 eV correspond to I
3d5/2 and I 3d3/2 respectively (Fig. 2b). They are related to Bi3+ in
2.3 Photoactivity tests
The photoactivity was evaluated by the degradation of RhB
under visible light (l $ 420 nm) irradiation. The visible light
was radiated by a 500 W high pressure xenon lamp (Changzhou
Yuyu Electro-Optical Device Co., Ltd. China) with a 420 nm
cutoff lter to ensure the desired irradiation light. The typical
photocatalytic degradation process was arranged as follows:
100 mL aqueous suspension of 5 mg Lꢀ1 RhB was placed in a
quartz beaker, and 20 mg photocatalyst was added. Prior to
irradiation, the suspensions were sonicated for 10 min and then
magnetically stirred in the dark for 30 min to obtain the
desorption–adsorption equilibrium. The suspensions were kept
under constant air-equilibrated conditions during their irradi-
ation. A magnetic stirrer was employed for continuous mixing.
At certain time intervals, 4 mL suspensions were sampled and
centrifuged by a TGL-16G centrifuge (Shanghai Anting Scientic
Instrument Factory, China) at 10 000 rpm for 15 min to remove
the particles. The upper clear liquid was analyzed by recording
the maximum absorption band (554 nm for RhB) and the Fig. 1 XRD pattern of BiOI and MnOx–BiOI.
This journal is ª The Royal Society of Chemistry 2013
J. Mater. Chem. A, 2013, 1, 8978–8983 | 8979

View Article Online
Journal of Materials Chemistry A
Paper
Fig. 3 (a) TEM image of BiOI; (b) HRTEM image and the corresponding FFT
pattern of BiOI; (c) TEM image of MnOx–BiOI (top view); (d) TEM image of MnOx–
BiOI (side view); (e) HRTEM image of MnOx on the BiOI surface.
ꢀ
of the {110} and {110} facets. As shown in the inset picture of
Fig. 3b, the angle labeled in the corresponding FFT image is 90ꢁ,
which is identical to the theoretical value for the angle between
ꢀ
the {110} and {110} facets. These observations also prove that
the BiOI single crystal exhibits the two {001} facets (top and
bottom surfaces).
Aer the photo-deposition of MnOx, it can be seen that MnOx
exists evenly on the surface of BiOI, and the thickness is about
80 nm (Fig. 3c and d). The HRTEM image of MnOx–BiOI shows
Fig. 2 High-resolution XPS spectra of BiOI and MnOx–BiOI: (a) Bi 4f, (b), I 3d, and
(c) Mn 2p regions.
˚
that the lattice spacing of 2.715 A is attributed to the (222) plane
˚
of cubic Mn2O3, and the lattice spacing of 1.663 A is ascribed to
the Bi–O band and I ꢀ in the BiOI layered structure.20–22 The two
peaks of the Mn 2p region at 641.8 and 654.2 eV are assigned to
Mn 2p3/2 and Mn 2p1/2 respectively, as shown in Fig. 2c. Based
on their binding energies, it can be concluded that MnOx (1.5 <
x < 2) forms on the surface of BiOI.24 It is also noted that the
content of iodine and bismuth decreases aer the photo-
deposition of MnOx. These results indicate a thicker and more
homogeneous coverage of MnOx formed on the BiOI.
the (102) plane of hexagonal MnO2. Since both Mn2O3 and
MnO2 are formed, the deposited manganese oxides are referred
to as MnOx for simplicity.24 This result is in agreement with the
XPS data.
3.2 Dramatic photocatalytic activity of MnOx–BiOI
The effects of MnOx deposition on the photocatalytic activity of
Fig. 3 shows the more detailed structural properties of BiOI nanoplates were evaluated by measuring the degradation
MnOx–BiOI. The TEM image (Fig. 3a) of BiOI shows that the of RhB in aqueous solution under visible light irradiation (l $
surface of BiOI is clean. The HRTEM image (Fig. 3b, viewed 420 nm). Fig. 4a shows the percentage removal of RhB by BiOI,
from the [001] axis) of BiOI clearly shows two sets of lattice Pt–BiOI and MnOx–BiOI. RhB self-photolysis without catalyst
fringes with a lattice spacing of 0.28 nm, corresponding to that under visible light irradiation is not observed, which indicates
8980 | J. Mater. Chem. A, 2013, 1, 8978–8983
This journal is ª The Royal Society of Chemistry 2013

View Article Online
Paper
Journal of Materials Chemistry A
Fig. 5 PL spectra of BiOI and MnOx–BiOI.
the PL spectra reects the higher rate of recombination.
Therefore, PL spectra are oen used to examine the efficiency of
charge carrier trapping, migration and transfer.24,25 With an
excitation wavelength of 400 nm, the PL spectra of MnOx–BiOI
and BiOI are presented in Fig. 5. It can be seen that BiOI shows a
strong emission peak at around 435 nm, which corresponds to
the direct electron and hole recombination at the band transi-
tion.25 However, the recombination rate of the photogenerated
carriers decreased aer MnOx loading, showing a higher sepa-
ration efficiency of photogenerated carriers. Thus, MnOx–BiOI
displays higher photocatalytic activity than pure BiOI.
Fig. 4 (a) The percentage removal of RhB by BiOI, Pt–BiOI and MnOx–BiOI under
visible light irradiation (l $ 420 nm); (b) PCD percentage of RhB in the initial 30
min by BiOI with different percentages of MnOx.
3.3 Cocatalyst selectivity of BiOI
Fig. 6 displays the results of the trapping experiment of the
active species during the photocatalytic reaction. It can be seen
that the photocatalytic degradation of RhB was not affected by
the addition of 1 mM IPA (a quencher of _OH). On the contrary,
the photocatalytic degradation of RhB decreased signicantly
with the addition of triethanolamine (TEOA, a quencher of h+)
and p-benzoquinone (BQ, a quencher of O2_ꢀ). Therefore, it can
be concluded that h+ and O2_ꢀ are the main active species of
BiOI in aqueous solution under visible light irradiation, rather
than _OH. However, it can be seen that h+ is more important
than O2_ꢀ for RhB degradation. This is in agreement with the
reported results.
that RhB is stable under visible light irradiation. At the same
time, our experimental data for acid orange II decolorization
with anatase P25 TiO2 as the catalyst shows that the dye
photosensitization process can be ignored. Aer 30 min of
visible light irradiation, RhB removal by BiOI is as low as 31%,
and Pt–BiOI also shows a relatively low photocatalytic perfor-
mance with a degradation ratio of 41.9%. Signicantly, the
photocatalytic activity of MnOx–BiOI displays a signicant
increase, inducing 78.8% degradation within 30 min. Fig. 4b
shows the PCD percentage of RhB in the initial 30 min by BiOI
with different percentages of MnOx. It can be found that the
best content of MnOx is 1.0 mol%. A lower or higher content
does not obtain better photocatalytic activity.
In a photocatalytic reaction, the catalyst activity is affected by
many factors, such as crystallinity, surface area and the reaction
conditions. Here, the crystallinity and reaction conditions of the
two types of photocatalysts are almost the same, and the surface
area of BiOI (0.83 m2 gꢀ1) is also close to that of MnOx–BiOI
(1.12 m2 gꢀ1). The only recognizable difference is the cocatalyst
MnOx.
What is the origin for MnOx–BiOI possessing high photo-
activity? It is known that MnOx is a deriving-hole-type cocata-
lyst. It can transfer holes, and then affect the separation
efficiency of photo-generated electron–holes, which is an
important factor in photocatalytic reactions.
Photoluminescence (PL) emerges from the recombination
Fig. 6 Active species trapping experiment of BiOI during the photocatalytic
of photo-generated electrons and holes. The higher intensity of reaction with 60 min visible light irradiation.
This journal is ª The Royal Society of Chemistry 2013
J. Mater. Chem. A, 2013, 1, 8978–8983 | 8981

View Article Online
Journal of Materials Chemistry A
Paper
Fig. 9 The mechanism of the cocatalyst selectivity of BiOI under visible light
irradiation (l $ 420 nm).
than _OH and O2_ꢀ. However, for Pt–BiOI, O2_ꢀ and h+ are the
main active species, and O2_ꢀ is more important than h+.
Therefore, it can be concluded that Pt promotes the transfer of
eꢀ and results in increased O2_ꢀ generation, and MnOx
promotes the transfer of h+. For conrmation of the different
roles of the cocatalysts, NBT was used to determine the amount
of O2_ꢀ generated by Pt–BiOI and MnOx–BiOI. As shown in
Fig. 8, Pt–BiOI can generate more O2_ꢀ than MnOx–BiOI and
BiOI. However, MnOx–BiOI does not show enhanced O2_ꢀ
generation compared with pure BiOI. This result is in agree-
ment with the active species trapping experiment.
Fig. 7 Active species trapping experiments during the photocatalytic reaction
with 60 min visible light irradiation: (a) MnOx–BiOI and (b) Pt–BiOI.
Base on the above discussion, the mechanism of the cocat-
alyst selectivity of BiOI is shown in Fig. 9. Under visible light
irradiation, for MnOx–BiOI, the h+ can transfer to MnOx and
degrade RhB. For Pt–BiOI, the eꢀ transfer to Pt and react with O2
to produce O2_ꢀ, but O2_ꢀ can not degrade aromatic compounds
(such as RhB) efficiently.33,34 So, BiOI is selective with deriving-
hole-type cocatalysts in enhancing the photocatalytic activity.
Deriving-electron-type cocatalysts can derive eꢀ, and
deriving-hole-type cocatalysts can derive h+. If the eꢀ and h+ play
different roles in the photocatalytic reaction, different cocata-
lysts may show different effects. For BiOI, h+ is more important
than O2_ꢀ (the single electron photoreduction results in O2_ꢀ
generation). So, as shown in Fig. 4a, the deriving-hole-type
cocatalyst MnOx may be more effective than the deriving-elec-
tron-type cocatalyst Pt for RhB degradation.
In order to study the reason of the cocatalyst selectivity of
BiOI, the active species trapping experiments of Pt–BiOI and
MnOx–BiOI were performed, and are shown in Fig. 7. For
MnOx–BiOI, it can be seen that h+ is the main active species of
BiOI in aqueous solution under visible light irradiation, rather
4 Conclusions
This paper presents a facile route for the preparation of MnOx–
BiOI heterogeneous nanostructure photocatalysts. They
exhibited higher photoactivity than BiOI and Pt–BiOI for the
degradation of RhB dye under visible light irradiation. We
found that BiOI is selective with deriving-hole-type cocatalysts
in enhancing the photocatalytic activity, and the reason of the
cocatalyst selectivity was also discussed. This nding may be
useful in bismuth-based photocatalysts to construct highly
efficient solar energy conversion systems. The research strategy
of cocatalyst selectivity and photoactivity in this work may
potentially be extended to other semiconductor photocatalysts
such as Bi2MoO6, BiVO4 and BiPO4.
Notes and references
1 C. Chen, W. Ma and J. Zhao, Chem.Soc.Rev., 2010, 39,4206–4219.
´
´
´
2 A. Kubacka, M. Fernandez-Garcıa and G. Colon, Chem. Rev.,
2012, 112, 1555–1614.
3 X. Zhang, Z. Ai, F. Jia and L. Zhang, J. Phys. Chem. C, 2008,
112, 747–753.
4 J. Henle, P. Simon, A. Frenzel, S. Scholz and S. Kaskel, Chem.
Mater., 2007, 19, 366–373.
Fig. 8 Transformationpercentage of NBTunder visible lightirradiation(l$ 420nm).
8982 | J. Mater. Chem. A, 2013, 1, 8978–8983
This journal is ª The Royal Society of Chemistry 2013

View Article Online
Paper
Journal of Materials Chemistry A
5 M. A. Gondala, X. Chang, M. A. Ali, Z. H. Yamania, Q. Zhou 20 X. Xiao and W. D. Zhang, J. Mater. Chem., 2010, 20,
and G. Ji, Appl. Catal., A, 2011, 397, 192–200. 5866–5870.
6 L. Ye, J. Liu, C. Gong, L. Tian, T. Peng and L. Zan, ACS Catal., 21 D. Zhang, M. Wen, B. Jiang, G. Lia and J. C. Yu, J. Hazard.
2012, 2, 1677–1683. Mater., 2012, 212, 104–111.
7 L. Ye, C. Gong, J. Liu, L. Tian, T. Peng, K. Deng and L. Zan, 22 C. Yu, J. C. Yu, C. Fan, H. Wen and S. Hu, Mater. Sci. Eng., B,
J. Mater. Chem., 2012, 22, 8354–8360. 2010, 166, 213–219.
8 Y. F. Fang, W. H. Ma, Y. P. Huang and G. W. Cheng, Chem.– 23 L. Zhu, C. He, Y. Huang, Z. Chen, D. Xia, M. Su, Y. Xiong,
Eur. J., 2013, 19, 3224–3229. S. Li and D. Shu, Sep. Purif. Technol., 2012, 91, 59–66.
9 Y. Feng, L. Li, J. Li, J. Wang and L. Liu, J. Hazard. Mater., 24 R. Li, F. Zhang, D. Wang, J. Yang, M. Li, J. Zhu, X. Zhou,
2011, 192, 538–544. H. Han and C. Li, Nat. Commun., 2013, 4, 1432.
10 Y. Fan, Y. Huang, J. Yang, P. Wang and G. Cheng, Environ. 25 L. Ye, L. Tian, T. Peng and L. Zan, J. Mater. Chem., 2011, 21,
Sci. Technol., 2011, 45, 1593–1600. 12479–12484.
11 J. Xu, W. Meng, Y. Zhang, L. Li and C. Guo, Appl. Catal., B, 26 L. Ye, K. Deng, F. Xu, L. Tian, T. Peng and L. Zan, Phys. Chem.
2011, 107, 355–362. Chem. Phys., 2012, 14, 82–85.
12 W. L. Huang and Q. Zhu, Comput. Mater. Sci., 2008, 43, 1101– 27 P. Ji, J. Zhang, F. Chen and M. Anpo, Appl. Catal., B, 2009, 85,
1108. 148–154.
13 L. Ye, L. Zan, L. Tian, T. Peng and J. Zhang, Chem. Commun., 28 G. A. Bowmaker, B. W. Skelton and A. H. White, Inorg. Chem.,
2011, 47, 6951–6953. 2009, 48, 3185–3197.
14 L. Ye, J. Chen, J. Liu, T. Peng, K. Deng and L. Zan, Appl. 29 L. Zhou, J. Liu and Z. Liu, J. Hazard. Mater., 2009, 172, 439–
Catal., B, 2013, 130–131, 1–7. 446.
15 J. Henle, P. Simon, A. Frenzel, S. Scholz and S. Kaskel, Chem. 30 S. A. Khan, N. Singh and K. Saleem, Eur. J. Med. Chem., 2008,
Mater., 2007, 19, 366–373. 43, 2272–2277.
16 X. Chang, J. Huang, C. Cheng, Q. Sui, W. Sha, G. Ji, S. Deng 31 A. E. Bolzana, T. Iwasita and A. J. Arvia, J. Electroanal. Chem.,
and G. Yu, Catal. Commun., 2010, 11, 460–464. 2003, 55, 49–60.
17 H. An, Y. Du, T. Wang, C. Wang, W. Hao and J. Zhang, Rare 32 F. Chen, H. Liu, S. Bagwasi, X. Shen and J. Zhang,
Met., 2008, 27, 243–250. J. Photochem. Photobiol., A, 2010, 215, 76–80.
18 X. Chang, J. Huang, Q. Tan, M. Wang, G. Ji, S. Deng and 33 J. L. Roberts Jr, T. S. Calderwood and D. T. Sawyer, J. Am.
G. Yu, Catal. Commun., 2009, 10, 1957–1961. Chem. Soc., 1983, 105, 7691–7696.
19 Y. Lei, G. Wang, S. Song, W. Fan, M. Pang, J. Tang and 34 Z. Wang, W. Ma, C. Cheng, H. Ji and J. Zhao, Chimica, 2011,
H. Zhang, Dalton Trans., 2010, 39, 3273–3278. 41, 1286–1297.
This journal is ª The Royal Society of Chemistry 2013
J. Mater. Chem. A, 2013, 1, 8978–8983 | 8983