A highly efficient sunlight driven ZnO nanosheet photocatalyst: Synergetic effect of p-doping and MoS2 atomic layer loading

Article abstract of DOI:10.1002/cctc.201402191

A novel kind of highly efficient photocatalyst composed of ultrathin P-doped ZnO nanosheets decorated with atomic MoS2 layers is reported. Under natural sunlight, 95% of the organic dyes can be degraded within six minutes. The photodegradation rate constant reaches up to 1.413 min^-1, which is 3.4 times larger than that of commercial P25 under the same reaction conditions. The superior photocatalytic activity of the hybrid photocatalyst can be attributed to the synergetic effects of many advantages, including enhanced light adsorption efficiency, suppression of charge recombination, improvement of interfacial charge transfer, and an increase in the number of reaction sites.

Full text of DOI:10.1002/cctc.201402191

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DOI: 10.1002/cctc.201402191
A Highly Efficient Sunlight Driven ZnO Nanosheet
Photocatalyst: Synergetic Effect of P-Doping and MoS2
Atomic Layer Loading
Yangyang Liu,[a] Shufan Xie,[a] Hui Li,[b] and Xianying Wang*[a]
A novel kind of highly efficient photocatalyst composed of ul-
trathin P-doped ZnO nanosheets decorated with atomic MoS2
layers is reported. Under natural sunlight, 95% of the organic
dyes can be degraded within six minutes. The photodegrada-
tion rate constant reaches up to 1.413 minÀ1, which is 3.4
times larger than that of commercial P25 under the same reac-
tion conditions. The superior photocatalytic activity of the
hybrid photocatalyst can be attributed to the synergetic effects
of many advantages, including enhanced light adsorption effi-
ciency, suppression of charge recombination, improvement of
interfacial charge transfer, and an increase in the number of re-
action sites.
To suppress the recombination of photogenerated carriers,
semiconducting photocatalysts are often decorated with noble
metal nanoparticles or other cocatalysts.[17] Noble metals are
rare and expensive, consequently alternative cocatalysts based
on inexpensive noble-metal-free cocatalysts have been studied
and have been shown able to outperform in the photocatalytic
efficiency of semiconducting oxides.[7,18–20] Among those cata-
lysts, molybdenum disulfide (MoS2) has been demonstrated as
an inexpensive and promising alternative to platinum for the
electrochemical and photochemical generation of hydrogen
from water. Xiang et al. reported that the H2 production rate
was greatly enhanced by the synergetic effect of MoS2 and
graphene as cocatalysts, for which TiO2 was used as the main
catalyst.[7] Wei et al. reported that the photocatalytic hydrogen
evolution activity over hexagonal ZnIn2S4 can be significantly
increased by loading MoS2 as a co-catalyst and that the photo-
catalytic activity of MoS2/ZnIn2S4 nanocomposites could be
even higher than that of Pt/ZnIn2S4 under similar reaction con-
ditions.[18] MoS2 cocatalyst has also been shown to be effective
in enhancing the photocatalytic performance of TiO2 nano-
belts,[19] CdS,[20] CdSe, etc. Recently, there is great interest in
two dimensional MoS2 catalysts for their potential applications
in nanodevices including batteries, sensors, transistors, etc.[21]
Owing to its large surface area, high electron mobility, moder-
ate bandgap, and rich active sites, 2D MoS2 is also expected to
have good photocatalysis qualities.
Ultra-efficient, eco-benign, and low-cost photocatalysts are
highly desired for renewable energy generation and environ-
mental remediation.[1–5] Semiconductors are commonly applied
to degrade organic pollutants, as they are generally non-toxic
and easy to obtain commercially. To achieve superior photoca-
talytic efficiency, the semiconductor should have adequate
band-edge positions, large surface-to-volume ratio, rapid
charge separation rate, and high carrier mobility.[6–8] Metal-
oxide based semiconducting nanomaterials, such as TiO2 and
ZnO, are particularly interesting in this regard.[3,9,10] A signifi-
cant amount of research has been devoted to modify the mor-
phologies of metal oxides to increase the specific area and/or
reduce photoinduced carrier recombination, by which better
photocatalyst performance can be achieved.[6,11–13] Compared
with the classical photocatalytic material TiO2, low dimensional
ZnO has the most abundant morphologies, which enables the
surface area to be tuned through a large range. By tuning the
size and morphology, the photocatalytic activity of ZnO has
been greatly improved. For example, hollow ZnO spheres,[14]
flower-like ZnO,[15] hierarchical ZnO,[16] and so on were shown
to have superior photocatalytic performance. In addition, ZnO
is more cost-effective than TiO2 and has larger charge mobility.
Herein, we report a nanocomposite photocatalyst based on
P-doped ZnO nanosheets and 2D MoS2. P-doped ZnO nano-
sheets with large surface area can offer high interfacial contact
area with the target pollution molecules. Mono or few layer
MoS2 is decorated on the surface of P-doped ZnO nanosheets.
The desirable 2D ZnO nanosheets loaded with the MoS2 co-
catalyst simultaneously increase the surface area and reduce
recombination, which greatly enhanced the photocatalyst per-
formance. The reaction rate constant of such hybridized
heterojunction nanostructure can reach up to 1.413 minÀ1
,
which is much larger than most reported values in the litera-
ture.[9,22] The superior photocatalytic performance is attributed
to a number of factors: First, the 2D nanosheet morphology of
a ZnO nanosheet has great properties, such as large surface
areas and permeable channels, which can facilitate light ad-
sorption and increase the effective photocatalytic reaction
area. These factors facilitate the movement of photoinduced
electron and hole pairs to transfer to the surface and act with
the organic molecules. Secondly, 2D–2D intimate contacts be-
tween ZnO/MoS2 heterojunctions can achieve fast charge
transfer from the conduction band (CB) of ZnO nanosheets to
[a] Y. Liu, S. Xie, Prof. X. Wang
School of Materials Science and Technology
University of Shanghai for Science and Technology
Shanghai, 200093 (P.R. China)
E-mail: xianyingwang@usst.edu.cn
[b] Dr. H. Li
Department of Physics and Materials Science
City University of Hong Kong
83 Tat Chee Avenue, Kowloon Tong (Hong Kong)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cctc.201402191.
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the CB of MoS2, reducing the recombination of carries and
thus increasing the reaction rate. Additionally, the potential
barrier at ZnO/MoS2 generates a driving force, which can fur-
ther help the charge separation. Thirdly, the loading of MoS2
can significantly enhance the light adsorption in the visible
range. Finally, doping the catalyst with phosphorous generates
abundant defect sties on the surface of the ZnO nanosheets,
which can trap light induced carriers. Taking advantage of the
synergetic effect of large surface area, 2D–2D ZnO/MoS2 con-
tact and P-doping, ZnO/MoS2 nanocomposite showed signifi-
cant higher photocatalytic performance than most of the
counterparts of other metal-oxide photocatalysts.
P-doped ZnO nanosheets were prepared using conventional
chemical vapor transportation and condensation (CVTC)
method as described elsewhere.[23] The amount of O2 gas
played an important role in controlling the morphologies and
sizes of ZnO nanosheets, as such the volume ratio of O2 and Ar
was kept at 1:10. Two dimensional MoS2 layers were prepared
by using a liquid exfoliation method. The details of the sample
preparation process can be found in the Supporting Informa-
tion. Shown in Figure 1a is the scanning electron microscope
(SEM) image of the P-doped ZnO nanosheets (loading:
0.1 wt% of MoS2). It can be seen that ZnO nanosheets are gen-
erally quite thin, transparent, and have irregular shapes. The di-
mensions of the nanosheets are in the range of tens of micro-
meters long and several micrometers wide. Atomic force mi-
croscope (AFM) scanning demonstrates that the ZnO nano-
sheets are generally around 50 nm thick (Figure S1). The dark
areas on the surface of ZnO nanosheets are described as MoS2,
which are generally a single layer or a few layers roughly 5–
15 nm to a side (Figure S2). Analysis by Raman and photolumi-
nesence (PL) reveal typical natures of 2D MoS2 (Figure S3).
Transmission electron microscope (TEM) images were taken to
further confirm the formation of ZnO/MoS2 heterojunctions. As
can be seen from the low resolution TEM image (Figure 1b),
transparent MoS2 layers can be clearly observed at the edges
of P-doped ZnO nanosheets. The HRTEM image taken from the
red circled area of Figure 1b displays two fringes with lattice
spacings of 0.52 nm and 0.27 nm, which correspond to the
(0001) planes of ZnO nanosheets and (100) planes of MoS2,
respectively. The lattices of ZnO nanosheets were partly dis-
torted, which is attributed to P doping. Also it can be found
that [0001] direction was per-
Figure 1. a) SEM image, b) low magnification TEM image, c) HRTEM image
taken from the selected red circles shown in b, d) full spectrum XPS (with
high-resolution Mo3d XPS as the inset) of hybridized P-doped ZnO nano-
sheets with the loading level of 0.1 wt% MoS2.
ure S4). These results suggest that the MoS2 layer is in close
contact with the ZnO nanosheets, which is essential for effec-
tive charge separation in the photocatalytic experiments. The
composition and the surface chemical bonding properties
were examined with XPS (Figure 1d). Except for the Zn and O
peaks, P and Mo peaks were also detected (Figure S5 and inset
of Figure 1d). The two typical peaks of Mo 3d were measured
at around 228.7 eV and 232 eV, which is consistent with a previ-
ous study.[7]
To identify the photocatalyst efficiency of the MoS2 hybrid-
ized P-doped ZnO nanosheets, two typical dyes: Methylene
blue (MB) and Rhodamine B (RhB), were selected as the indica-
tors. The reaction process is monitored spectrophotometrically
by measuring the degradation of MB and RhB, which exhibit
a distinct spectral profile with an adsorption maximum at l=
664 and 554 nm, respectively. Natural sunlight was used as the
pendicular to edges of the nano-
sheets. The detailed growth
mechanisms of P-doped ZnO
nanosheets will be presented
elsewhere. Furthermore, the se-
lected area diffraction (SAED)
pattern in the inset of Figure 1c
shows milky rings besides the
ZnO diffraction spot, which
arises from the stacking of few
Figure 2. a) Absorption spectra of MB solution at different time after irradiating under the natural solar light using
P-doped ZnO/0.1wt% MoS2 as the photocatalyst. b) The ln(C/C0) vs. time curves of MB under five different photo-
catalyst: the control P25, P-doped ZnO nanosheets with the loading level of MoS2 at 0, 0.01, 0.1, 1 wt%, respec-
tively. c) The apparent rate constants of MB photodegradation on the five different photocatalyst as described in
layers of MoS2 with different
crystal orientations. HRTEM
images taken at another area
demonstrate similar results (Fig- b.
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light source for all the experi-
ments. From Figure 2a, it is clear
that the MB adsorption peak de-
creases dramatically when pho-
tocatalyzed by ZnO nanosheets-
MoS2. After exposure to sunlight
for only 2 mins, 83% of MB dye
had decomposed and, interest-
ingly, after 6 mins that value had
increased to 95%. The degrada-
tion of RhB followed a similar
profile (Figure S6).
To investigate the effect of
MoS2 cocatalyst, the photode-
gradation measurements with
different loading amounts of
MoS2 were carried out while
other experiment conditions
were kept at the same. The load-
ing level of the MoS2 was set to
be 0, 0.01, 0.1, and 1 wt%, with
respect to the total composi-
tions. The photocatalyst efficien-
cy of commercial P25 was also
measured for comparison. The
original C/C0 values which were
calculated according to the UV/
vis spectra can be found in
Figure 3. a) Transient photocurrent response and b) Absorption spectra of P25, ZnO nanosheets and ZnO/
0.1 wt%-MoS2. c) Tentative mechanisms of photocatalytic process.
Table S1. All the kinetic curves show linear relationships with
time and can be fitted using the kinetic equation ln(C/C0)=
Àkt (Figure 2b), demonstrating that the photodegradation re-
action of MB can be considered as a pseudo-first-order reac-
tion. Distinct comparisons of the rate constants are given in
Figure 2c. Noticeably, the reaction rate constant for P25 is
0.422 minÀ1, whereas the value is significantly larger for ZnO
can increase the effective charge transport channels. It is evi-
dent from the UV/vis diffusion absorption spectrum (Figure 3b)
that the light harvesting capacity become stronger owing to
the loading of MoS2 on the surface of ZnO nanosheet. The
bandgap of ZnO is 3.37 eV, therefore it can only adsorb the
light in the UV region. However, the band gap of mono MoS2
layer is 1.87 eV,[24] which closely matches the solar spectrum so
that visible energy from the natural solar light can also be ad-
sorbed.
nanosheets with 0.1 wt% MoS2, 1.413 minÀ1 Even only a small
.
amount of MoS2 (0.01 wt%) acted as cocatalyst, remarkably in-
creased degrading rate of organic moleculars can also be
achieved. The photocatalytic activity improved with increasing
amount of cocatalyst from 0.01 to 0.1 wt%, however, further
increase of MoS2 led to a decrease in the efficiency. This is rea-
sonable because a thick MoS2 layer would block the sunlight,
such that light could not be absorbed by whole catalyst scope,
reducing the effective catalyst area.
The photodegradation mechanism of ZnO/MoS2 photocata-
lyst is schematically illustrated in Figure 3c. When the semicon-
ductor samples are irradiated with photons whose energy is
higher than its bandgap, holes and electron pairs can be creat-
ed and react with H2O and O2 on the surface of the semicon-
ductors. These reactions generate highly reactive hydroxyl radi-
À
C
C
cals ( OH) and superoxide anion radicals ( O2 ) that can de-
grade organic molecules (Figure 3c). Compared with metal
oxide nanoparticles or nanowires/nanotubes, the effective light
adsorption and photodegradation reaction areas of ZnO nano-
sheets are greatly enlarged because of the two dimensional
feature. As the ZnO nanosheets are extremely thin, the photo-
generated carriers inside ZnO can be easily transported to the
surface and contribute to the photocatalytic activity. Moreover,
the surface oxygen defects (Figure S7) caused by P doping can
also play an important role in the trapping of photocarriers.[25]
From the band diagram (Figure 3d and Figure S8), it is clear
that the conduction band (CB) of ZnO is higher than that of
MoS2, which facilitates the electron transportation from ZnO to
MoS2. Therefore, the heterojunction between P-doped ZnO
To examine the significantly enhanced photocatalyst efficien-
cy for the MoS2 hybridized P-doped ZnO nanosheets, transient
photocurrent response and UV/vis spectra were employed for
a range of samples: control P25, P-doped ZnO nanosheets and
ZnO/0.1 wt%-MoS2. Impressively, the photocurrent density of
ZnO/0.1wt%-MoS2 is about 3 times as high as that of the pure
P-doped ZnO electrode and 9 times that of P25 (Figure 3a).
The photocurrent enhancement of the MoS2/ZnO photocata-
lyst indicates an enhanced separation rate of photoinduced
electrons and holes, which could be attributed to the synerget-
ic effect of fast charge transfer between 2D–2D contacts of
ZnO and MoS2. Compared with 0D–0D, 1D–0D and other types
of contacts, 2D–2D contacts have larger contact areas, which
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rolidone solution (NVP) and then sonicated for 400 mins at low
temperatures. The working power of the sonicator was 350 W.
After sonication, the dispersion was centrifuged at 11000 rpm for
60 min. The top supernatants were transferred to a glass bottle.
The content of the solid MoS2 in the solution was measured to be
and MoS2 can help the separation of the photogenerated
charges. (Figure 3d). In addition, the photocatalytic activity of
ZnO nanosheets with 0.1 wt% MoS2 displayed the best activity
of all the samples and this could be attributed to mainly the
increased absorbance and scattering of photons through
excess MoS2 in the photosystem. The nanoscale MoS2 mono-
layer is also highly active, which may provide additional sites
for the photodegradation reaction. On the basis of the above
analysis, it can be concluded that the notable enhancement of
photocatalytic activity of ZnO/MoS2 composite photocatalyst
can be attributed to the positive synergetic effect of the fol-
lowing: increase of light adsorption and photodegradation re-
action areas by tailoring the morphologies, improvement of in-
terfacial charge transfer by forming 2D–2D contacts, suppres-
sion of charge recombination and enhancement of light ad-
sorption by MoS2 loading and P doping, and increase of the
active reaction sites by loading mono layer MoS2.
0.29 mgmLÀ1
.
Formation of ZnO nanosheet/MoS2 hybrid photocatalyst
40 mg of the P doped ZnO nanosheets were dispersed in 100 mL
distilled water, then 1.5 mL, 0.15 mL, 0.015 mL aforementioned
2D MoS2 solution were added to the ZnO nanosheets suspension
respectively to change the weight ratio of MoS2/ZnO from 1 wt%
to 0.01 wt%. The mixed solution was ultrasonically handled for
30 min and magnetically stirred for 2 h. The solution was dried
under 1108C for 24 h to get the mixed powder. The obtained
hybrid nanocomposites were used to do photocatalytic experi-
ments under sunlight. TiO2 nanopowder is commercial available
P25 (Degussa Co., Ltd., Germany).
In summary, we demonstrated a highly efficient P-ZnO/MoS2
composite photocatalyst which exhibits a high photodegrada-
tion rate constant of 1.413 minÀ1 when degrading MB dyes
under natural sunlight irradiation. Large and ultrathin ZnO
nanosheets were successfully synthesized by CVTC method
where P doping amount and oxygen carrier gas are critical in
obtaining such nanostructures. Plenty of carries generated
inside the ZnO crystalline have opportunity to transfer to the
surface and act with the organic molecules. The formation of
mono or few layer of MoS2 makes it easy to attach to the sur-
face of ZnO nanosheets by Van-der-Waals force and form 2D–
2D heterojunctions. The superior photocatalytic activity of the
hybrid can be attributed to the synergetic effects of many ad-
vantages including enhanced light adsorption efficiency, sup-
pression of charge recombination, improvement of interfacial
charge transfer, and an increase in the number of reaction
sites. This study will provide important inspirations for the ra-
tional design of novel high efficient photocatalysts.
Characterizations
The morphologies of the photocatalysts were examined by using
a field-emission scanning electron microscopy (FE-SEM, Quanta
FEG, FEI) and high resolution transmission electron microscopy
(HRTEM, Tencai G20, FEI). The thickness of ZnO nanosheets were
characterized by using Atomic force microscope (AFM, Cypher,
Oxford Inc.). XPS experiments were performed by an upgraded PHI
5000C ESCA System with MgKa irradiation (hn=1253.6 eV). Absorp-
tion spectra were measured using UV/vis absorption spectropho-
tometer (UV-vis-2550).The photocurrent response of the samples
was measured by using a semiconductor characterization system
(Keithley 4200). A xenon lamp was employed as the irradiation
source.
Photocatalytic degradation measurement
The photocatalytic activities of the as-prepared samples were
tested for the degradation of MB and RhB in solution under
sunlight. Case in MB, 40 mg of the hybrid photocatalysts with
different MoS2 loading levels were placed in 40 mL MB aque-
ous solution with the concentration of 10 mgLÀ1. Then the so-
lution was magnetically stirred without radiation in the dark
for 10 mins in order to judge of the absorption capacity of
sample to MB. The photodegradation experiments were carried
out under natural sunlight for 8 min (the power intensity was
measured to be 1.8 mWcmÀ2). The solutions were sampled at
intervals of 2 mins., then analyzed by recording variations in
the absorption band (664 nm) in the UV/vis spectra of MB
using UV-vis-2550. The effect of commercial P25 photocatalyst
was also examined under the same reaction conditions for
comparisons.
Experimental section
Fabrication of P doped ZnO nanosheets
P-doped ZnO nanosheets were fabricated using conventional
chemical vapor transport and condensation (CVTC) method. Single
crystal silicon coated with a thin layer of Au film was used as the
substrate. The phosphor pentoxide (P2O5, Alfa Aesar 99.99%) nano-
powders mixed with equal amount of ZnO (Alfa Aesar 99.99%) and
graphite (200 mesh, Alfa Aesar 99.9%) powders were used as pre-
cursors for the ZnO nanosheets growth. The weight amount of
P2O5 in the precursors was kept at 15%. High purity argon (Ar,
99.999+%) and oxygen (O2, 99.999+%) with the volume ratio of
10:1 were used as the carrier (reaction) gas at a constant total flow
rate of 110 sccm. The growth was carried out at 10008C for
30 mins and the samples were then cooled down to room temper-
ature. The white powders on the surface of silicon substrate were
then collected for further hybridization with MoS2.
Acknowledgements
We acknowledge the financial support from the Natural Science
Foundation of China (51072119), Innovation Program of Shang-
hai Municipal Education Commission (12ZZ139), the Key Project
Synthesis of two-dimensional MoS2
Single or few layer MoS2 was prepared using liquid exfoliation
method. 50 mg MoS2 powers were added into 20 mL 1-vinyl-2-pyr-
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[14] H. Zeng, W. Cai, P. Liu, X. Xu, H. Zhou, C. Klingshirn, H. Kalt, ACS Nano
2008, 2, 1661.
[15] M. Ahmad, Y. Y. Shi, A. Nisar, H. Y. Sun, W. Shen, M. Wei, J. Zhu, J. Mater.
Chem. 2011, 21, 7723.
of Chinese Ministry of Education (12057), and The Hujiang Foun-
datiion of China (B1406).
[16] F. Lu, W. Cai, Y. Zhang, Adv. Funct. Mater. 2008, 18, 1047.
[17] M. Murdoch, G. I. N. Waterhouse, M. A. Nadeem, J. B. Metson, M. A.
Keane, R. F. Howe, J. Llorca, H. Idriss, Nat. Chem. 2011, 3, 489.
[18] L. Wei, Y. G. Chen, Y. P. Lin, H. S. Wu, R. S. Yuan, Z. H. Li, Appl. Catal. B
2014, 144, 521.
[19] W. Zhou, Z. Yin, Y. Du, X. Huang, Z. Zeng, Z. Fan, H. Liu, J. Wang, Small
2013, 9, 140.
[20] X. Zong, H. J. Yan, G. P. Wu, G. J. Ma, F. Y. Wen, L. Wang, C. Li, J. Am.
Chem. Soc. 2008, 130, 7176.
[21] M. Chhowalla, H. S. Shin, G. Eda, L. J. Li, K. P. Loh, H. Zhang, Nat. Chem.
2013, 5, 263.
[22] T. Xu, L. Zhang, H. Cheng, Y. Zhu, Appl. Catal. B 2011, 101, 382.
[23] P. D. Yang, H. Q. Yan, S. Mao, R. Russo, H. J. Choi, Adv. Funct. Mater.
2002, 12, 323.
[24] J. Mann, P. M. Odenthal, M. Isarraz, D. Le, E. Precisdo, D. Barroso, K. Ya-
maguchi, T. S. Rahman, R. Kawakami, L. Bartels, Adv. Mater. 2014, 26,
1399.
[25] J. Yan, G. Wu, N. Guan, L. Li, Z. Li, X. Cao, Phys. Chem. Chem. Phys. 2013,
15, 10978.
Keywords: doping · nanomaterials · photocatalysis · sulfide ·
zinc
[1] M. R. Hoffmann, S. T. Martin, W. Choi, D. W. Bahnemann, Chem. Rev.
1995, 95, 69.
[2] Y. Okamoto, S. Ida, J. Hyodo, H. Hagiwara, T. Ishihara, J. Am. Chem. Soc.
2011, 133, 18034.
[3] I. Paramasivam, H. Jha, N. Liu, P. Schmuki, Small 2012, 8, 3073.
[4] Z. W. Seh, S. Liu, M. Low, S.-Y. Zhang, Z. Liu, A. Mlayah, M.-Y. Han, Adv.
Mater. 2012, 24, 2310.
[5] X. Wang, G. Liu, Z.-G. Chen, F. Li, L. Wang, G. Q. Lu, H.-M. Cheng, Chem.
Commun. 2009, 3452.
[6] J. M. Macak, M. Zlamal, J. Krysa, P. Schmuki, Small 2007, 3, 300.
[7] Q. J. Xiang, J. G. Yu, M. Jaroniec, J. Am. Chem. Soc. 2012, 134, 6575.
[8] O. Akhavan, ACS Nano 2010, 4, 4174.
[9] C. Tian, Q. Zhang, A. Wu, M. Jiang, Z. Liang, B. Jiang, H. Fu, Chem.
Commun. 2012, 48, 2858.
[10] Y. Li, W. Xie, X. Hu, G. Shen, X. Zhou, Y. Xiang, X. Zhao, P. Fang, Langmuir
2010, 26, 591.
[11] S. Chakrabarti, B. K. Dutta, J. Hazard. Mater. 2004, 112, 269.
[12] H. Li, J.-W. Cheng, S. Shu, J. Zhang, L. Zheng, C. K. Tsang, H. Cheng, F.
Liang, S.-T. Lee, Y. Y. Li, Small 2013, 9, 37.
Received: April 2, 2014
Revised: April 29, 2014
[13] J. Zhang, W. X. Que, Sol. Energy Mater. Sol. Cells 2010, 94, 2181.
Published online on July 17, 2014
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