Preparation and photocatalytic property of hexagonal cylinder-like bipods ZnO microcrystal photocatalyst

Article abstract of DOI:10.1016/j.dyepig.2012.05.027

Single crystalline ZnO with hexagonal cylinder-like bipods morphologies were successfully synthesized via a cationic surfactant-assisted hydrothermal microemulsion route. The structure, morphologies and properties of the as-prepared samples were determined using X-ray diffraction, scanning electron microscopy, photoluminescence spectrum and Ultraviolet and Visible absorption spectroscopy. The photocatalytic activities of the obtained products were evaluated by the degradation of Reactive Brilliant Red K-2BP in aqueous solution under a variety of conditions. Under the optimum condition, approximately 99.5% decolorization efficiency within 45 min and 65.3% TOC removal efficiency within 3 h were achieved, which were higher than that by the commercial ZnO. Moreover, the degradation products were analyzed by a gas chromatography coupled with mass spectrometry system and the probable pathways for the formation of the intermediates were proposed. The photocatalytic results indicated that the as-prepared ZnO showed good photocatalytic activity and it could be considered as a promising photocatalyst for dyes wastewater treatment.

Full text of DOI:10.1016/j.dyepig.2012.05.027

Dyes and Pigments 95 (2012) 443e449
Contents lists available at SciVerse ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Preparation and photocatalytic property of hexagonal cylinder-like bipods ZnO
microcrystal photocatalyst
*
Yumin Liu , Hua Lv, Shuangqing Li, Xinyan Xing, Guoxi Xi
College of Chemistry and Environmental Science, Henan Normal University, Xinxiang 453007, Henan, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 25 February 2011
Received in revised form
Single crystalline ZnO with hexagonal cylinder-like bipods morphologies were successfully synthesized
via a cationic surfactant-assisted hydrothermal microemulsion route. The structure, morphologies and
properties of the as-prepared samples were determined using X-ray diffraction, scanning electron
microscopy, photoluminescence spectrum and Ultraviolet and Visible absorption spectroscopy. The
photocatalytic activities of the obtained products were evaluated by the degradation of Reactive Brilliant
Red K-2BP in aqueous solution under a variety of conditions. Under the optimum condition, approxi-
mately 99.5% decolorization efficiency within 45 min and 65.3% TOC removal efficiency within 3 h were
achieved, which were higher than that by the commercial ZnO. Moreover, the degradation products were
analyzed by a gas chromatography coupled with mass spectrometry system and the probable pathways
for the formation of the intermediates were proposed. The photocatalytic results indicated that the as-
prepared ZnO showed good photocatalytic activity and it could be considered as a promising photo-
catalyst for dyes wastewater treatment.
29 April 2012
Accepted 10 May 2012
Available online 29 June 2012
Keywords:
ZnO
Hydrothermal microemulsion method
Photocatalytic
Reactive Brilliant Red K-2BP
Intermediate compounds
Degradation mechanism
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
a larger fraction of the UV spectrum and more light quanta [6]. In
addition, it has been reported that ZnO shows better activity than
Large amounts of colored dye wastewaters released into envi-
ronment mainly by dyestuff and textile industry lead to severe
surface water and groundwater contamination [1,2]. Conventional
methods such as physical methods, chemical methods or their
combinations are used for decolorization of these dyes [3]. Never-
theless, these methods are usually non-destructive, inefficient,
costly and result in secondary pollution. Thus, it is necessary to
develop treatment methods that are more effective in eliminating
dyes from wastewaters.
Advanced oxidation processes (AOPs) have been developed to
meet the increasing need of an effective wastewater treatment,
which are characterized by the generation of highly oxidative
hydroxyl radicals in the homogeneous or heterogeneous phase [4].
2
that of TiO in the photodegradation of some dyes in aqueous
solutions [7,8].
As is well known, the size and morphology of semiconductors
have great influences on their properties. Up to date, different
morphologies and sizes of ZnO have been successfully synthesized,
including nanowires [9], nanowhiskers [10], tubes [11], star-like
[12], tetrapod-like [13] and flower-like [14], etc. However, despite
great progress in this field, the shape-controlled synthesis of ZnO
materials still remains a remarkable challenge. Various approaches
have been employed to synthesize ZnO with unique microstruc-
tures, such as thermal decomposition method [15], homogeneous
precipitation [16], hydrothermal method [17], solegel processing
[18], microwave method [19], hydrothermal microemulsion [20]
and microemulsion method [21], etc. Among them, hydrothermal
microemulsion method is a promising method for synthesizing
ideal ZnO materials with special morphology. The main advantage
of this method is low reaction temperature and short processing
time that prevent agglomeration in the formed particles.
Among AOPs, cheaply available nontoxic semiconductors (TiO
ZnO) are the most extensively used photocatalysts due to their high
photocatalytic activity. It is well known that TiO is universally
considered as the most active photocatalyst, while ZnO is found to
be a suitable alternative to TiO because its photodegradation
mechanism has been proven to be similar to that of TiO [5]. The
biggest advantage of ZnO compared with TiO is that it absorbs
2
,
2
2
2
Recently, studies on synthesis of ZnO composed of hexagonal
microstructures have been reported [22e24]. For example, Sun and
Qiu have reported synthesis of single-crystalline ZnO microtubes
with hexagonal shape by gas method [22]. Bitenc et al. have re-
ported on the fabrication of hexagonal bipods ZnO by a facile-
2
*
Corresponding author. Tel.: þ86 373 3326335; fax: þ86 373 3326336.
E-mail address: ymliu2007@163.com (Y. Liu).
0143-7208/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.dyepig.2012.05.027

4
44
Y. Liu et al. / Dyes and Pigments 95 (2012) 443e449
template-free method in a mixture of water and ethylene glycol
23]. However, few efforts have been made to synthesize ZnO with
Reactive Brilliant Red K-2BP solution. All experiments were carried
out in a photoreaction apparatus as reported in our previous study
[25]. A 300 W high-pressure mercury lamp with the strongest
emission at 365 nm was used as light source (Shanghai Jiguang
Company, China). The temperature of the reactions was controlled
at room temperature by circulating water. The pH value of the
solution was controlled by adding 0.5 M HCl or NaOH solution. In all
experiments, 500 ml of the dye solution containing appropriate
quantity of ZnO suspensions was used. The suspension was soni-
cated for 10 min and stirred for 30 min in the dark in order to reach
the adsorptionedesorption equilibrium. At specific time intervals,
5 ml of the sample was withdrawn and centrifuged to separate the
catalyst before analysis.
[
hexagonal cylinder-like bipods morphology by hydrothermal
microemulsion route to the best of our knowledge. In this paper,
ZnO with hexagonal cylinder-like bipods morphology was
successfully synthesized via a cationic surfactant-assisted hydro-
thermal microemulsion route. The structure, morphologies and
properties of the as-prepared products were characterized by X-ray
diffraction (XRD), scanning electron microscopy (SEM), trans-
mission electron microscopy (TEM), photoluminescence (PL)
spectrum and Ultraviolet and Visible absorption spectroscopy
(
UVeVis). The photocatalytic activities of the prepared ZnO
microcrystal photocatalyst were evaluated by the degradation of
Reactive Brilliant Red K-2BP and a possible degradation pathway of
the reactive dye was proposed.
For the determination of the dye concentration, UVeVis spec-
trophotometer (Model T60, Beijing Purkinje General Instrument
Company, China) was used at
lmax of 537 nm. The total organic
2
. Materials and methods
carbon (TOC) of the dye before and after decolorization was also
measured by using a TOC analyzer (Apollo 9000, Terkmar Dohr-
mann, USA).
2.1. Materials
The degradation products were identified using a gas chroma-
tography coupled with mass spectrometry (GC/MS) system. The
samples collected at different time intervals during the degradation
process were acidified and extracted with dichloromethane. The
extracts were dehydrated using anhydrous sodium sulfate. After-
ward, the dehydrated solution was concentrated to 1 ml. The GC
system (TRACE GC, Thermo Fishier) was equipped with a TR-35MS
The dye of Reactive Brilliant Red K-2BP (purity ꢀ 98%) was
purchased from the Eighth Dye Chemical Factory of Shanghai
(
Shanghai, China) and used directly without further purification. All
other chemicals were of reagent grade and used as received.
2
.2. Preparation of hexagonal cylinder-like bipods ZnO
capillary chromatographic column (30 m ꢂ 0.25 mm, 0.25
mm) and
In a typical experimental procedure, two identical solutions
coupled to a MS system (DSQII, Finnigan). The injection was con-
ducted on a splitless mode, and the injector temperature was
were separately prepared by dissolving CTAB (2 g) in 20 ml of
cyclohexane and 4 ml of n-butanol. Then, 2 ml of 0.5 M zinc acetate
dihydrate and 2 ml of 0.25 M methenamine aqueous solutions were
added to the two solutions, respectively. After vigorous stirring at
room temperature for 30 min, the two optically transparent
microemulsion solutions were mixed and stirred for another
ꢁ
300 C with helium served as the carrier gas at the flow rate of
ꢃ1
1.0 ml min . The extracted samples were chromatographed under
the following temperature gradient: the initial column temperature
ꢁ
ꢁ
ꢁ
ꢃ1
ꢃ1
was held constant at 50 C for 5 min, increased at 10 C min to
ꢁ
100 C and kept constant for 2 min, then ramped at 8 C min to
250 C and maintained constant for 5 min, further increased at
20 C min to 280 C and retained constant for 5 min, and finally
raised at 25 C min to 300 C and stayed constant for 5 min.
ꢁ
3
0 min. The resulting microemulsion was transferred into a Teflon-
ꢁ
ꢁ ꢁ
ꢃ1
lined stainless-steel autoclave and heated at 140 C for 14 h, fol-
lowed by cooling to room temperature naturally. White products
were separated by centrifugation and washed with deionized water
and absolute ethanol several times. Then, the obtained products
ꢁ
ꢃ1
ꢁ
3. Results and discussion
ꢁ
were dried in a vacuum at 50 C for 12 h.
3.1. Characterization of the ZnO microcrystal photocatalyst
2.3. Characterization of hexagonal cylinder-like bipods ZnO
A typical XRD pattern of the synthesized ZnO is shown in Fig. 1.
The crystal structure of the synthesized ZnO was determined by
All the diffraction peaks in Fig. 1 can be well indexed to the
hexagonal wurtzite ZnO (JCPDS card No. 65-3411). The results
indicate that the products consist of pure phase and no character-
istic peaks can be found from other impurities. The sharp and
strong diffraction peaks reveal that the as-synthesized products are
of high purity and good crystallinity.
XRD (Bruker D8 Advance, Germany) using graphite monochromatic
ꢁ
copper radiation (Cu K
a
) in the 2
q
range of 20e80 . The crystal
morphology of ZnO was observed by SEM (JEOL JSM-63901, Japan)
and TEM (JEOL JEM-2100, Japan). The specific surface area of the
ZnO powder was determined, in terms of the N adsorption on the
2
powder, using the standard BrunauereEmmetteTeller (BET)
procedure. The measurement was performed using a volumetric
adsorption apparatus (NOVA Surface Area Analyzer Station A, USA).
The optical absorption spectra of ZnO were recorded by UVeVis
spectrophotometer (Lambda 17, PerkinElmer, USA). Prior to
UVeVis analysis the ZnO samples were ultrasonically dispersed in
deionized water at room temperature. The room temperature
photoluminescence (PL) spectra of ZnO microcrystal were
measured by using a Fluorescence Spectrophotometer (FP-6500,
Japan) equipped with a Xenon lamp at an excitation wavelength of
Fig. 2 shows the typical SEM and TEM images of the prepared
and commercial ZnO. It can be observed that the synthesized ZnO
exhibits an obviously different microstructure compared to the
commercial ZnO. As shown in Fig. 2a and b, hexagonal cylinder-like
bipods ZnO about 1
mm in diameter and 2.5 mm in length are
observed and a bipod structure can be clearly seen in the middle of
the hexagonal cylinder. A typical TEM image of the single hexagonal
cylinder-like bipod is shown in Fig. 2d. It is clear that the
morphology of samples is in accordance with the results of the
SEM. The corresponding selected area electron diffraction (SAED)
pattern of the synthesized ZnO demonstrates that the grown
products are single-crystalline and grown along the c-axis direction
in preference. On the contrary, various microstructures were
observed from the SEM image of the commercial ZnO (Fig. 2c).
Although the commercial ZnO exhibits a smaller particle size than
that of the prepared ZnO, it also can be seen from Fig. 2c that the
3
25 nm.
2.4. Photocatalytic experiments
The photocatalytic activities of the hexagonal cylinder-like
bipods ZnO were evaluated by photocatalytic degradation of

Y. Liu et al. / Dyes and Pigments 95 (2012) 443e449
445
individual bipod crystallite took place along the polar c-axis by
means of the incorporation of growth units on the growth inter-
faces (0001) and thus hexagonal cylinder-like bipods ZnO crystals
were formed ultimately.
The absorption of UVeVis light is an important factor for the eval-
uation of photocatalyst property. Fig. 3 shows the UVeVis absorption
spectra of the prepared and commercial ZnO. The prepared ZnO
microcrystal photocatalyst has a broad absorption band from ultravi-
olet to visible region and the maximum absorption peak is found at
375 nm. On the contrary, the commercial ZnO shows narrower and
weaker absorption in this region. The broad band-edge absorption of
the synthesized ZnO may be attributed to its bipods microstructure and
further investigation is needed for detailed explanation.
The room temperature photoluminescence (PL) spectra of the
prepared and commercial ZnO were recorded as shown in Fig. 4. For
the commercial ZnO, it has an UV emission band at about 383 nm
and several blue and green emission peaks at 420e550 nm. The UV
emission peak at 383 nm is due to the recombination of photo-
generated electrons and holes, while the blue and green emission
peaks are possibly associated with oxygen vacancies [27]. For the as-
prepared ZnO, only a very strong peak at 386 nm corresponding to
the near band-edge emission is observed, which means that the
synthesized ZnO are highlycrystallinewith no oxygenvacancies. It is
commonly accepted that high-quality ZnO crystals only emit UV
light. Therefore, it is reasonably believed that the synthesized ZnO
crystals with hexagonal cylinder-likebipods morphologyareof good
quality and may have wide application in the photocatalytic field.
Fig. 1. XRD pattern of the synthesized ZnO.
commercial ZnO particles are easy to agglomerate with each other,
which can result in the decreasing light utilization rate and lower
photocatalytic activity. The specific surface area of the synthesized
and commercial ZnO, measured using the BET method, were 8.60
and 2.47 m /g, respectively, which means that the hexagonal shape
and bipod structure can increase the surface area of the prepared
ZnO and consequently enhance its light absorption.
2
Previous report has been demonstrated that dumbbell-like ZnO
twinned crystals can be formed by the hydrothermal process using
KBr or NaNO
2
as the mineralizer [26]. In such a hydrothermal
3.2. Degradation
þ
þ
process, K or Na may be taken as the bond bridge between the
growth units to form a crystal nucleus of the dumbbell-like twin-
ning crystal. In our case, the growth units of [Zn(OH)
3.2.1. Spectral changes of Reactive Brilliant Red K-2BP during
decolorization process
2ꢃ
4
]
can be
bonded by the CTAB to form the nucleus of hexagonal cylinder-like
bipod crystal. To decrease the surface energy, the growth of the
Fig. 5 shows the UVeVis spectrum obtained for the Reactive
Brilliant Red K-2BP solution during the decolorization process
Fig. 2. SEM images of the synthesized ZnO (a and b) and commercial ZnO (c). (d) Low-magnification TEM image of the synthesized ZnO. Inset in part d is the SAED pattern of the
synthesized ZnO.

4
46
Y. Liu et al. / Dyes and Pigments 95 (2012) 443e449
Fig. 5. Variation of UVeVis absorbance spectra of Reactive Brilliant Red K-2BP with
different reaction time under UV light irradiation in the presence of the synthesized
ZnO. Experimental conditions: [ZnO] ¼ 0.5 g/l, pH ¼ 6.0, and [dye] ¼ 50 mg/l.
Fig. 3. UVeVis absorption spectra of the synthesized ZnO (a) and commercial ZnO (b).
taken along time in a typical experiment. Regarding the dye spec-
trum, it is characterized by three bands in the ultraviolet region
located at 247, 288 and 378 nm and by one band in the visible
region, with a maximum located at 537 nm. The absorbance peaks
in the UV region can be assigned to the benzene, triazine and
naphthalene rings [28], whereas the band observed in the visible
region can be attributed to chromophore-containing azo linkage of
Reactive Brilliant Red K-2BP [29]. By comparing the original spec-
trum (t ¼ 0 min) with that achieved within 45 min of decoloriza-
tion, it is evident that the treated dye sample is almost colorless and
doesn’t show significant absorbance in the visible region, indicating
that color removal is practically complete. The disappearance of the
absorbance peak at 537 nm reflects, unequivocally, the breakdown
in the chromophoric group. However, the spectrum in the ultravi-
olet region shows that the dye is not completely mineralized, even
though the absorption intensity is reduced within the ultraviolet
range. The slower decrease of the intensities of the bands in the
ultraviolet region, with respect to that of the azo bond, can be
attributed to the formation of intermediates, resulting from the
decolorization of the azo dye, which still contain benzoic-and
naphthalene-type rings [30].
increases sharply from 11.5 to 99.5% after 45 min irradiation when
the concentration of the catalyst increases from 0 to 0.5 g/l. Higher
reaction rates at higher amount of catalyst loading may be
explained in terms of the complete utilization of incident photons
striking on the catalyst surface and/or availability of active sites at
the surface [31]. Nevertheless, it should be pointed out that the
decolorization efficiency decreases to 97.9% with further increasing
the ZnO dosage to 0.7 g/l. These observations can be rationalized in
terms of availability of active sites on ZnO surface and the pene-
tration of photo activating light into the suspension. Firstly, high
catalyst concentration may lead to the aggregation of ZnO particles,
which consequently causes a decrease in the number of surface
active sites and reduces the catalytic activity. Secondly, high cata-
lyst concentration can increase opacity of the suspension and light
scattering, and thus decreases the passage of irradiation through
the sample [32]. On the basis of these results, 0.5 g/l is selected as
the optimum dosage of ZnO for the subsequent experiments.
3.2.3. Effect of initial pH
The influence of pH on the decolorization of Reactive Brilliant
Red K-2BP was studied with pH ranging from 4.0 to 10.0. As it is
presented in Fig. 7, the color removal increases significantly from
3
.2.2. Effect of catalyst dosage
The influence of catalyst dosage on the decolorization efficiency
against time is illustrated in Fig. 6. The decolorization efficiency
Fig. 6. Effect of catalyst dosage on the photocatalytic degradation of Reactive Brilliant
Red K-2BP. Experimental conditions: pH ¼ 6.0 and [dye] ¼ 50 mg/l.
Fig. 4. PL spectra of the ZnO samples at room temperature.

Y. Liu et al. / Dyes and Pigments 95 (2012) 443e449
447
Fig. 7. Effect of initial pH on the photocatalytic degradation of Reactive Brilliant Red K-
BP. Experimental conditions: [dye] ¼ 50 mg/l and [ZnO] ¼ 0.5 g/l.
Fig. 8. Effect of initial dye concentration on the photocatalytic degradation of Reactive
Brilliant Red K-2BP. Experimental conditions: pH ¼ 6.0 and [ZnO] ¼ 0.5 g/l.
2
compared with the commercial ZnO powders. Similar results were
reported earlier for the degradation of organic compound by ZnO
photocatalyst with novel morphology. Sun et al. had synthesized
dumbbell-shaped ZnO and found that 16e22% higher TOC removal
efficiency was obtained by the dumbbell-shaped ZnO compared to
commercial ZnO [36]. The good performance for the degradation of
the dye by the synthesized ZnO may be attributed to its high
specific surface area and excellent optical properties (as shown in
Figs. 3 and 4).
7
3.7% at a pH of 4.0 to 99.5% at a pH of 6.0, and then increases
slightly with the increase of pH to 10.0. The point worthy to
mention is that the results indicate alkaline conditions can promote
photocatalytic performance. The possible explanation is that ZnO is
a poor photocatalyst in the oxidative degradation of Reactive Bril-
liant Red K-2BP at pH 4.0, because it corrodes in aqueous acidic
media [33]. In alkaline medium, excess of hydroxyl anions typically
act as scavenger of holes on the surface of ZnO and become
hydroxyl radicals with strong oxidation ability after they lose
ꢄ
electrons. Consequently, a higher concentration of OH species is
3.4. Degradation pathway of Reactive Brilliant Red K-2BP
formed, and the decolorization efficiency is enhanced [34]. Because
the difference between the decolorization efficiency in the basic
solution (about 10.0) and in its natural solution (about 6.0) is very
small, the pH value of 6.0 is chosen as a moderate and optimum pH
value and the experiments is followed under this pH value.
The samples of Reactive Brilliant Red K-2BP oxidized at different
intervals were collected to determine the intermediate compounds
by GC/MS and four compounds were detected (Isocyanatobenzene
(D
1 2 3 4
), Aniline (D ), Phenol (D ), Phthalic acid (D )). A tentative
degradation pathway based on the GC/MS identification is
proposed in Fig. 10. We theorize that the initial Reactive Brilliant
Red K-2BP and the intermediates are degraded by direct oxidation,
hydrolysis, and free radical attack. The CeN bonds are initially
3
.2.4. Effect of initial dye concentration
It is important from an application point of view to study the
dependence of dye concentration on the photocatalytic reaction
rate. As shown in Fig. 8, the effect of initial dye concentration was
investigated by varying the initial concentration from 30 to 100 mg/
l. The decolorization efficiency decreases with the increase in the
initial dye concentration. This behavior is attributed to that the
amount of dye adsorbed on the catalyst surface increases with the
increase of dye concentration, but the intensity of light and irra-
diation time are constant, so the path length of photons entering
broken down to form compounds S
CeS bonds of compounds S (oxidized by active radicals at the
same time), S , S and S are cleaved to yield the corresponding
1 2 3 4
, S , S and S . Then the CeCl,
1
2
3
4
ꢄ
the solution decreases and consequently the OH radicals formed
on the surface of ZnO decrease and thus results in the decrease of
photodegradation efficiency [35].
3.3. Comparison of the photocatalytic activity of the synthesized
and commercial ZnO
To evaluate the photocatalytic activity of the synthesized
hexagonal cylinder-like bipods ZnO, the decolorization and TOC
removal experiments using the synthesized ZnO and commercial
ZnO as catalyst were carried out. As shown in Fig. 9, the decolor-
ization efficiency of the dye by the synthesized ZnO is higher than
that by the commercial ZnO after 45 min of reaction time. After 3 h
of reaction time, the TOC removal efficiency of the dye by the
synthesized ZnO and commercial ZnO is 65.3% and 49.8%, respec-
tively. It is evident that the synthesized ZnO is more efficient for the
mineralization and decomposition of the model compound as
Fig. 9. Decolorization (after 45 min irradiation) and TOC removal (after 3 h irradiation)
efficiencies of Reactive Brilliant Red K-2BP by the synthesized ZnO and commercial
ZnO. Experimental conditions: [dye] ¼ 50 mg/l, [ZnO] ¼ 0.5 g/l and pH ¼ 6.0.

4
48
Y. Liu et al. / Dyes and Pigments 95 (2012) 443e449
Fig. 10. Proposed pathways of the photocatalytic degradation of Reactive Brilliant Red K-2BP.
compounds D
aqueous solution to form S
yield compound D . Compounds D
radicals yielding S and D , which could be further oxidized to yield
compound S10. Compound S can be oxidized by active radicals
yielding compound S and generating D by the breakdown of the
aromatic ring. The compounds S , S10 and D are further oxidized to
yield low molecular weight compounds.
1
, D
2
, S
5
and S
, which then could be decarboxylated to
can be attacked by active
6
. Compound D
1
can be hydrolyzed in
surfactant-assisted hydrothermal microemulsion process. The
characterization results show that the prepared ZnO microcrystal
photocatalyst is pure and belongs to the hexagonal wurtzite family.
The photocatalytic activity of the prepared ZnO has been evaluated
by the degradation of Reactive Brilliant Red K-2BP in aqueous
solution. Operational parameters such as ZnO dosage, pH value and
dye concentration have significant influence on the photo-
degradation efficiency. For degradation of 50 mg/l of Reactive
Brilliant Red K-2BP, the most suitable operation conditions are:
catalyst dosage 0.5 g/l, pH value 6.0. Under the optimum conditions,
the decolorization and TOC removal efficiencies are achieved 99.5%
(45 min) and 69.3% (3 h), respectively, which is higher than that by
the commercial ZnO. In addition, the possible degradation
7
2
2
9
3
5
8
4
6
4
4
. Conclusion
Single crystalline ZnO with hexagonal cylinder-like bipods
morphologies have been successfully synthesized by a cationic

Y. Liu et al. / Dyes and Pigments 95 (2012) 443e449
449
pathways of the dye have been proposed. Overall, the good optical
absorption properties of the as-prepared ZnO may be very inter-
esting for further application on catalyst and chemical sensors.
[17] Zhang ZQ, Mu J. Hydrothermal synthesis of ZnO nanobundles controlled by
PEO-PPO-PEO block copolymers. Journal of Colloid and Interface Science
2007;307:79e82.
[
18] Rani S, Suri P, Shishodia PK, Mehra RM. Synthesis of nanocrystalline ZnO
powder via solegel route for dye-sensitized solar cells. Solar Energy Materials
and Solar Cells 2008;92:1639e45.
Acknowledgments
[19] Komarneni S, Bruno M, Mariani E. Synthesis of ZnO with and without
microwaves. Materials Research Bulletin 2000;35:1843e7.
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20] Sun GB, Cao MH, Wang YH, Hu CW, Liu YH, Ren L, et al. Anionic surfactant-
assisted hydrothermal synthesis of high-aspect-ratio ZnO nanowires and
their photoluminescence property. Materials Letters 2006;60:2777e82.
The authors gratefully acknowledge the financial support from The
Youth Fund of Henan Normal University (Grant No. 01036400069) and
The National NaturalScience Foundation of China (Grant No. 51174083).
[21] Agrell J, Germani G, Järås SG, Boutonnet M. Production of hydrogen by partial
oxidation of methanol over ZnO-supported palladium catalysts prepared by
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