Controllable fabrication of various ZnO micro/nanostructures from a wire-like Zn-EG-AC precursor via a facile solution-based route

Article abstract of DOI:10.1016/j.materresbull.2011.03.030

In this paper, ZnO particles with various morphologies were prepared though a facile solution-based route. The complexes Zn-EG-AC (EG: ethylene glycol; AC: CH₃COO^- groups) obtained by reaction of anhydrous zinc acetate and EG were used as precursors. It is found that the precursor could transform into ZnO in water with no need of assistant of additional alkali as it is sensitive to water. At the same time, it is well dispersed in reaction medium (water and ethanol). Experimental results showed that ZnO particles with various morphologies, such as the hexagonal rings, the hexagonal plates, the tubes, the prisms, and some interesting hierarchical structures, could be obtained by controlling hydrolysis of precursor in water and water/ethanol medium through finely tuning the experimental parameters. The success of shape-controllable fabrication was related intimately with the Zn-EG-AC precursor used in our synthesis.

Full text of DOI:10.1016/j.materresbull.2011.03.030

Materials Research Bulletin 46 (2011) 1283–1289
Contents lists available at ScienceDirect
Materials Research Bulletin
journal homepage: www.elsevier.com/locate/matresbu
Controllable fabrication of various ZnO micro/nanostructures from
a wire-like Zn–EG–AC precursor via a facile solution-based route
Chungui Tian, Wei Li, Qi Zhang, Kai Pan, Honggang Fu *
Key Laboratory of Functional Inorganic Material Chemistry, Ministry of Education of the People’s Republic of China, Heilongjiang University, Harbin 150080, PR China
A R T I C L E I N F O
A B S T R A C T
Article history:
In this paper, ZnO particles with various morphologies were prepared though a facile solution-based
Received 25 October 2010
Received in revised form 18 March 2011
Accepted 29 March 2011
Available online 5 April 2011
ꢀ
route. The complexes Zn–EG–AC (EG: ethylene glycol; AC: CH
3
COO groups) obtained by reaction of
anhydrous zinc acetate and EG were used as precursors. It is found that the precursor could transform
into ZnO in water with no need of assistant of additional alkali as it is sensitive to water. At the same time,
it is well dispersed in reaction medium (water and ethanol). Experimental results showed that ZnO
particles with various morphologies, such as the hexagonal rings, the hexagonal plates, the tubes, the
prisms, and some interesting hierarchical structures, could be obtained by controlling hydrolysis of
precursor in water and water/ethanol medium through finely tuning the experimental parameters. The
success of shape-controllable fabrication was related intimately with the Zn–EG–AC precursor used in
our synthesis.
Keywords:
A. Nanostructures
A. Semiconductor
B. Chemical synthesis
ß 2011 Elsevier Ltd. All rights reserved.
1
. Introduction
Precise control of size and shape is current research topics in the
and condensation methods [10]. Besides, the rod-like ZnO particles
were successfully prepared with the assistance of ethylenediamine
and NaOH through a hydrothermal route [11]. Hexagonal ZnO
areas of nanomaterials [1]. Especially, the control of the
morphology has received special attention because of the essential
effect of the morphology on surface atomic arrangement and
coordination of the particles, and consequently, the performance of
the materials [2,3]. Zinc oxides (ZnO), a wide band gap (3.37 eV)
semiconductor, have great potential in the fields of catalysis,
sensor, photoelectric transformation and piezoelectric devices [4].
The morphology plays key role on governing the property of the
ZnO materials. Typically, the (0 0 0 1) and (0 0 0 1¯ ) facets of the ZnO
have exhibited specific adsorption activity for CO during the
synthesis of methanol [5], and for photodegradation reaction of the
organic contaminations [6]. Recently, the shape-related optical
properties of ZnO were detailed reviewed by Djuri sˇ i c´ et al. [7].
Furthermore, the effect of microstructures on the photo-electric
transformation performance of ZnO has been analyzed by Cao et al.
single-crystal slices with predominant (0 0 0 1) and (0 0 0 1¯ ) facets
were fabricated by poly(ethylene glycol)-assisted chemical bath
deposition route [12]. Recently, the large arrays of hierarchical
ordered crystal architectures of ZnO were designed by ‘‘sequential
nucleation and growth’’ strategy [13,14]. In addition, ZnO
nanoparticles were prepared from nanowhisker precursor through
a simple solvothermal route [15]. Above analyses showed that
there are already large successes in shape-controllable fabrication
of ZnO micro/nanostructures. Nevertheless, it still holds intensive
interest and remains a big challenge for preparing various ZnO
micro/nanostructures via a facile process. Doing it real should be
important for further applications of ZnO-based materials.
In this paper, we reported the fabrication of ZnO particles with a
wide variety of morphologies via an effective solution chemical
route (SB route) under alkali-free conditions. As known, the
physical process needs usually harsh reaction conditions in
company with lower yield, which are disadvantageous for the
practical application of the materials. In this regards, SB routes are
promising for the preparation of ZnO crystals due to their merits of
low cost, mild reaction condition and potential mass production. In
the route, tuning the balance of nucleation and growth process is
key factor to control the microstructure of ZnO crystals [11,13,14].
Notably, the precursor to ZnO plays important role for tuning the
balance based on their intrinsic ability to release Zn source [16].
The typical precursor to ZnO included zinc salts or water-soluble
[
8]. All of the studies showed the importance of morphology in the
areas of the technological applications and fundamental studies for
ZnO materials. Consequently, it is not surprising that much effort
has been devoted into controllable synthesis of ZnO particles.
Wang and co-workers have reported the fabrication of ZnO
nanobelts by the vapor deposition technique [9]. ZnO nano-nails
and nano-bridges were obtained through thermal vapor transport
*
Corresponding author. Tel.: +86 451 86608458; fax: +86 451 86673647.
2+
3 2 3 2 3 4
ZnO complex, such as Zn(CH COO) , Zn(NO ) , Zn(NH ) , etc.
E-mail address: fuhg@vip.sina.com (H. Fu).
0025-5408/$ – see front matter ß 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.materresbull.2011.03.030

1
284
C. Tian et al. / Materials Research Bulletin 46 (2011) 1283–1289
Recently, it was reported that the metal–ethylene glycol (metal–EG)
complexes could be used as precursor to prepare corresponding
oxides via solid-state pyrolysis process [17–19]. Typical samples
included Sn–EG, V–EG and Zn–EG. It has been found that Zn–EG
complexes were sensitive to water, that is, could hydrolyze to form
ZnO in pure water with no adding additional alkali [19]. This
phenomenon stimulated us think if the characteristic could be
utilized to controllably synthesize corresponding oxides. Herein, we
demonstrate, for the first time, the complexes obtained by reaction
recorded on a Rigaku D/Max-2550 (40 kV, 200 mA) diffractometer
using Cu K radiation with wavelength of = 0.15406 nm. FT-IR
spectra were recorded on a PerkinElmer Spectrum One spectrom-
eter using KBr pellets in the range of 400–4000 cm . Thermo-
gravimetric analysis was performed on a TG (TA, Q600) thermal
analyzer under air with a heating rate of 10 K/min. The nitrogen
adsorption–desorption isotherms were measured at 77 K using an
Micromeritics Tristar. Before measurement, the samples were out
gassed at 150 8C for 4.5 h, the specific surface area of the materials
was calculated by the Brunauer–Emmett–Teller (BET) theory.
a
l
ꢀ1
of anhydrous zinc acetate and EG (refereed as Zn–EG–AC in here, EG:
ꢀ
ethylene glycol, AC: CH
3
COO groups) could act as a suitable
precursor for fabricating ZnO crystals with various morphologies,
including typically hexagonal rings, hexagonal plates, tubes, prisms,
twinned discs and some hierarchical structure. Compared to the
methods reported before, present route has several obvious
advantages. First, ZnO particles with a variety of morphologies
and uniform shape (up to 15 kinds) were easily fabricated by simply
tuning the experimentalparameters. Second, nodangerous reagents
3. Results and discussion
Scheme 1 is a schematic procedure to prepare ZnO micro/nano
structures. The process includes the first preparation of Zn–EG–AC
precursor (Step 1), and its subsequent hydrolysis to form ZnO
crystals (Step 2). The precursor was characterized by IR, TG, XRD,
and SEM techniques. In IR spectra (Fig. S1), the broad peak at about
ꢀ
1
3
(such as strong alkali NaOH and NH ) were used in whole
3416 cm is assigned to
n(O–H) from adsorbed water, while the
ꢀ1
preparation process. The shape-controllable synthesis was related
intimately with the characteristics of Zn–EG–AC precursor used in
here, such as easily adjusting the hydrolysis rate by water amount
and good dispersity in reaction medium.
peaks located at 2830–2960 cm are indexed to the vibration of
ꢀ
1
C–H bands. In addition, the peaks in the range of 1000–1250 cm
can be indexed to (CH ), (C–C) and (C–O) bands. As control, IR
r
2
n
n
spectra of EG is also provided. It can be seen that most peaks in IR
spectra of EG and Zn–EG–AC spectra are same. The results indicate
the presence of EG unit in the precursor. In addition, the two peaks
2
. Materials and methods
ꢀ1
at 1425 and 1561 cm in Zn–EG–AC precursor are ascribed to the
ꢀ
2.1. Chemicals
n
as and
n
s
(O 55 C–O–) bands of CH
3
COO groups, indicating the
ꢀ
presence of CH
3
COO in the products. TG analysis is also
Zinc acetate dihydrate (Zn(CH
ethylene glycol (EG), ethanol, cetyltriethylammonium bromide
CTAB), sodium dodecyl sulfate (SDS), polyvinyl pyrrolidone (PVP,
K30), glucose and starch were purchased from Tianjin Kermel
Chemical Reagent Co., Ltd. PEO–PPO–PEO (P123) was purchased
form Sigma. All reagents were used as received without further
purification.
3
COOH)
2
ꢁ2H
2
O, Zn(Ac)
2
ꢁ2H
2
O),
performed to give deep insight on structure of Zn–EG–AC
precursor. As shown in Fig. S2, the loss weight before 100 8C
(about 3.5%) is due to the residual ethanol in the products from the
washing process. A major mass loss is observed at around 350 8C,
attributing to the decomposition of the Zn–EG–AC. Final weight
loss of as-prepared Zn–EG–AC within 350-600 8C is about 43%.
Based on proposed structure by Zhang et al. [20], the theoretical
loss weight from precursor to ZnO is about 35.13% calculated as
below:
(
2
.2. The preparation of ZnO micro/nanostructures
The anhydrous zinc acetate was obtained by heating
1
25:45 ꢀ 81:38
Zn(CH
3
COOH)
2
2
ꢁ2H O at 100 8C for 12 h. To prepare the precursor
Ratio of weight loss ¼
ꢂ 100% ¼ 35:15%
125:45
Zn–EG–AC, 4.0 g of anhydrous zinc acetate and 40 mL of the EG
were added in a 250 mL round-bottom flask and the solution was
heated at 160 8C for 1 h. After naturally cooling to room
temperature, the white solids were separated by centrifugation
and washed with anhydrous ethanol for 3 times. The products
were saved under vacuum at 40 8C. The reaction could be scaled-up
by increasing the amount of the anhydrous zinc acetate and EG.
where 125.45 is the theoretical molecular weight of Zn(OCH2-
CH O), and 81.38 is that of ZnO. The value (35.13%) is very close to
value tested by our TG results. The deviation between experimen-
2
tal (about 43%) and theoretic (35.13%) values should be due to
ꢀ
presences of CH
3
COO groups. Compared with –OCH
2
CH
2
O–, the
ꢀ
CH
3
COO have similar molecular but with little coordination
‘The ZnO micro/nanostructures were prepared by the hydrolysis
number (2:1). Thus, the ratio of ZnO will decrease in precursor. In
addition, XRD pattern of the precursor shows an intensive peak at
about 108 (Fig. S3), which is characteristic to M (metal)–EG
composites (metal = Sn, V and Zn) [17–19]. By combination of XRD,
IR, TG analyses and previous work, the proposed structure of
precursor should be Zn (OCH
< x + y < 2. For convenience, we call the precursor as Zn–EG–
AC. SEM analysis shows that the precursor are the long wire with
the diameter about 500 nm and length of several tens micrometers
of Zn–EG–AC precursor in water/ethanol solvent (or pure water).
Typically, for the preparation of ZnO nanorings, 4.0 g of Zn–EG–AC
precursor and 0.5 g of CTAB were added into the solvent that was
2
composed of 20 mL of H O and 20 mL of ethanol. After stirring at
room temperature for 1 h, the mixture was transferred to a 50 mL
Teflon-lined stainless steel autoclave. The autoclave was heated at
00 8C for 10 h. Final white products were separated by centrifuga-
tion, and purified through washing with distilled water and ethanol
for several times, finally dried at 60 8C. The experimental
parameters, including reaction temperature, time, kinds of surfac-
tant and volume ratioof ethanol/water (denoted as R), were tuned to
studythe influence of the parameters onthe morphologies of ZnO. In
all experiment, 4.0 g of Zn–EG–AC precursor was used.
ꢀ
2
CH
2
O)x(CH
3
COO )y, where
1
1
2.3. Characterizations
The morphology of the samples was studied by Hitachi S-4800
scanning electron microscope. X-ray diffraction pattern was
Scheme 1. Schematic process for fabrication of ZnO (n ꢃ 15).

C. Tian et al. / Materials Research Bulletin 46 (2011) 1283–1289
1285
500 nm and length about 1
m
m are main products. The organic
structure-directing agents play a key role for controlling morphol-
ogy of ZnO micro/nano-sized particles. To demonstrate this, the
CTAB was replaced with other capping reagent, including SDS, PVP,
P123, and saccharose. Typical SEM figures are given in Fig. 3. When
SDS was added, the thin ZnO nanoplates with diameter below
1
mm were obtained (Fig. 3a). Also, some large plate-like structures
are observed. As PVP was used, the twinned ZnO hexagonal with
unsymmetrical morphology are mainly products (Fig. 3b). At the
same time, a little of hollow rings could also be observed. In the
case of using P123 and saccharose, the twinned ZnO hexagonal
with unsymmetrical morphology are obtained (Fig. 3c and d).
However, the size and the thickness of two samples are different.
The particles from saccharose have a larger size and thickness.
Based on above results, one can see that the ZnO with other
morphologies other than nanorinds could be obtained when CTAB
was replaced by other capping agent, further demonstrating
importance of CTAB in the formation of ZnO nanorings. Recently,
Li’s and Peng’s groups reported the synthesis of ring-like ZnO
particles by sodium bis(2-ethylhexyl) sulfosuccinate [22] and
polyacrylamide [23] assisted routes. It was proposed that the
formation of ZnO nanorings should be contributed to a selected
etching process. However, the hexagonal plates with corrosive
centre (that should be intermediate products) are rarely observed.
In our work, we have observed the intermediates for the first time,
which provided a direct evidence for the formation process of ZnO
rings. Based on the above results, it was proposed that the
formation of ZnO rings is relative with a CTAB-assisted etching
process. Importantly, it also indicates that the microstructures of
ZnO could be easily tuned as rings, plates, prisms, etc.
Fig. 1. (a) SEM image and (b) XRD pattern of ZnO nanorings.
We found that the ZnO morphology could be easily tuned in
pure water assisted by different surfactants. Specifically, with
assistant of 1 g P123, ZnO prisms with the length about 2
mm and
diameter about 1 m are obtained when the synthesis was
m
(
Fig. S4a). Also, a magnified SEM image indicates the existence of
performed in 40 mL of water at 100 8C for 10 h (Fig. 4a). From the
inset of Fig. 4a, we can seen that the prisms are composed of
twinned hexagonal prisms that have a larger population of
nonpolar {0 1 1¯ 0} faces than polar {0 0 0 1} ones [4]. By replacing
many rumples on the wire surface (Fig. S4b).
ZnO particles were obtained by controlling the hydrolysis of
Zn–EG–AC precursor in water/ethanol solvent. Fig. 1a shows SEM
image of ZnO nanorings that was obtained by hydrolysis of the
P123 with PVP, the ZnO microtubes are formed as shown in Fig. 4b.
precursor in 20 mL ethanol + 20 mL H
2
O (R = 1) at 100 8C for 10 h
The tubes are twined with the diameter about 1
mm and length
with assistant of 0.5 g CTAB. As shown, the products are mainly
composed of the hexagonal rings with thickness about 400 nm and
about 3 m. The thickness of the tube wall is about 100 nm as
shown in inset of Fig. 4b. In addition, the cobble-like ZnO are
m
diameter about 2
= 31.78, 34.48, 36.28, 47.58, 56.68, 62.88, and 67.88 are,
respectively, indexed to (1 0 0), (0 0 2), (1 0 1), (1 0 2), (1 1 0),
mm. In XRD pattern (Fig. 1b), the peaks located at
formed when the SDS was selected as structure-directed agents.
The size of the ‘‘cobbles’’ is in the range of 20–100 mm. The high
2u
magnification SEM images (inset in Fig. 4c and d) show that the
cobbles are composed of the many sheets with thickness about
300 nm. Above results indicated important effect of surfactants
and ratio of ethanol to water on ZnO microstructure. Notably,
further experiments indicted that the ZnO particles with uniform
shape and narrower size distribution could be fabricated via this
facile solution-based route by tuning reaction temperature,
reaction, and the kinds of capping agents (Fig. 5a–i, Fig. 5a’–i’ is
corresponding figure of particle size distribution). Typical samples
include asymmetric hexagonal prisms (Fig. 5a), drums (Fig. 5b),
twinned hexagonal prisms (Fig. 5c), yo-yo balls (Fig. 5d),
hamburgers (Fig. 5e), cauliflowers-1 (Fig. 5f), hoofs (Fig. 5g),
cauliflowers-2 (Fig. 5h) and acalephs (Fig. 5i). Noteworthy is that
the ‘‘cauliflower’’ and ‘‘twinned prism’’ have represented different
microstructures for different samples (for example, cauliflower-
like particles in Fig. 5f and h, twinned hexagonal prisms in Figs. 4b
and 5b). XRD patterns of the typical samples were given in Figs. S5–
S7. From the XRD patterns, we can see that the samples are
crystalline ZnO with hexagonal structure (Wurtzite, JCPDS card no.
36-1451).
(
(
1 0 3) and (1 1 2) diffractions of hexagonal structure ZnO
wurtzite) (JCPDS card no. 36-1451). The experimental parameters,
including reaction time, CTAB and R value, have obvious effect on
the microstructure of resulting ZnO crystals. Fixing the other
parameters, the solid hexagonal ZnO plates with size about 2 um
are obtained after performing the reaction for 1 h (Fig. 2a). With
prolonging time to 5 h, the hexagonal plates with corrosive centre
are main products as shown in Fig. 2b. Hollow hexagonal plates
(hexagonal rings) are obtained as predominated product after
performing the reaction for 10 h as depicted in Fig. 1a. Besides the
reaction time, the CTAB are also important factor that affect ZnO
shape. More specifically, ZnO thin plates with predominant
(
0 0 0 1) and (0 0 0 1¯ ) facets [21] were gained in the absence of
CTAB, as shown in Fig. 2c. The diameter of the plates is about
00 nm with thickness of 50 nm. As 0.2 g CTAB was added, ZnO
5
hexagonal plate in company with a little of ZnO hexagonal ring are
observed as shown in Fig. 2d. Increasing the dose of CTAB to 0.5 g,
the hexagonal rings were formed with high yields. The effect of R
value is also very obvious. Based on SEM analyses, we found that
the products are composed of irregular ZnO particles as R is 9/1.
While decreasing R to 0, the hexagonal prisms with diameter about
Above results indicate that Zn–EG–AC complex is a suitable
precursor for the controllable fabrication of ZnO particles with

1
286
C. Tian et al. / Materials Research Bulletin 46 (2011) 1283–1289
Fig. 2. SEM images of ZnO particles obtained in the case: (a) R = 1:1, 100 8C, 1 h, 0.5 g CTAB; (b) R = 1:1, 100 8C, 5 h, 0.5 g CTAB; the inset is magnified SEM image of the sample;
c) R = 1:1, 100 8C, 10 h, without CTAB; (d) R = 1:1, 100 8C, 10 h, 0.1 g CTAB; (e) R = 9:1, 100 8C, 10 h, 0.5 g CTAB; (f) R = 0, 100 8C, 10 h, 0.5 g CTAB.
(
either single morphological or hierarchical (assembly) structure.
Although great success was done previously, it still holds intensive
interest and remains a key challenge in broadly tuning ZnO
microstructure. There are two obvious characteristics for our
present synthesis. First, ZnO with a wide variety of microstructures
could be fabricated by simply tuning the experimental parameters.
Second, Zn–EG–AC precursor could transform into ZnO by using
2
H O as alkali without need of using additional basic agents, such as
2
Fig. 3. SEM image and of ZnO structures obtained by hydrolysis of Zn–EG–AC in 20 mL H O + 20 mL ethanol at 100 8C for 10 h with assistance of SDS, (b) PVP, (C) P123 and (d)
saccharose.

C. Tian et al. / Materials Research Bulletin 46 (2011) 1283–1289
1287
Fig. 4. SEM images of ZnO structures obtained by hydrolysis of Zn–EG–AC in 40 mL of H
2
O at 100 8C for 10 h with assistance of (a) P123, (b) PVP and (c and d) SDS. The insets in
Fig. 3a–c are corresponding high-magnification SEM image of the samples.
ammonia, NaOH. In contrast, the excessive alkali needs to be
adopted for transformation of the precursors into ZnO in many
previous works. Based on our analysis, the advantages of our
method are related with the Zn–EG–AC precursor. The Zn–EG–AC
complexes have a wire-like microstructure, which could acts as a
observed (Fig. 6, curve a). However, we can see that the XRD
patterns of the product are different with origin Zn–EG–AC. Two
typical new peaks located at about 58 and 138 indicate formation
of layered hydroxide zinc acetate (LHS-Zn) based on the
previous reports of Zhang’s and Jouini’s groups [20,28]. As no
additional acetate was used in the synthesis, the acetate in LHS-
Zn should be from precursor. This further indicated presence of
acetate groups in the Zn–EG–AC precursor. This observation
further sustains the results obtained by TG and IR analyses.
When the time prolonged to 2 h, the peaks corresponding to ZnO
and LHS-Zn could be observed simultaneously (Fig. 6, curve b).
The intensity ratio of ZnO phase to LHS-Zn phase gradually
increased as the increase of reaction time (Fig. 6, curve c).
Finally, the phase pure ZnO were obtained after 8 h of hydrolysis
reaction (Fig. 6, curve d). In general, the more direct medium
‘‘solid’’ precursor for ZnO. As demonstrated before, the solid
precursor could act as the slow-release reagent that provides an
opportunity for proper regulating balance between the rates of
nucleation and growth [24]. This indicated that, by using ‘‘solid’’
Zn–EG–AC as precursor, we can easily tune the balance of the
nucleation and growth rates in the synthesis of ZnO particles, and
thus regulate ZnO shape. On the other hand, the Zn–EG–AC
2+
precursor composed of Zn coordinated with alkoxy groups have a
similar structure with the metal alkoxides (such as titanium tert-
2
butoxide). Because H O is a more strong alkali than EG group, thus
2
ꢀ
the precursor could transform into ZnO by using water as ‘‘alkali’’.
In previous reports, the ‘‘solid’’ precursors used to prepare ZnO
were composed of inorganic compounds from a precipitation
reaction that have relatively high stability. For example, the
precursor remained stabilization after hydrothermal treatment at
proposed in the formation of ZnO are Zn(OH)
4
. To demon-
strate this speculation, the followed experiments were per-
formed. The reaction was firstly performed at 70 8C for 1 h. After
centrifugation, the supernatant (colorless, transparent) was
collected followed by heating at 100 8C for 1 h. The solution
became turbid and finally white precipitation (ZnO) was
1
00 8C for 4 h. Thus, the excessive alkali was adapted to effectively
2
ꢀ
transform the precursors into ZnO. At the same time, only several
hierarchical ZnO structures were obtained in these ‘‘solid’’
precursor routes, including the flower-like cupped-end ZnO
microrod bundles [25], the hierarchical ZnO with a bladed
bundle-like architecture [26] and ring-like nanosheets standing
on spindle-like rods [27].
obtained. The results showed that the existence of Zn(OH)
in the supernatant, implying further that the direct medium
4
2
ꢀ
should be Zn(OH)
4
in present synthesis.
Based on above analysis, we proposed that, in our synthesis,
ZnO was formed through three steps as follows:
ZnꢀEGꢀAC ! LHS-Zn ! ZnðOHÞ4 ꢀ ! ZnO
2
Recently, the study by Zhang’s group indicated that the wire-
like precursor containing Zn and EG could transforming into the
LHS-Zn under moisture [19]. Also, many study indicated that the
One of main characteristics of Zn–EG–AC precursor is its well-
dispersion in reaction medium (both water and ethanol, Fig. S8).
This characteristic should be favorable for a heterogeneous
nucleation process. Both of the characteristics have contributed
into the fine and wide adjusting of the ZnO morphology. Zn–EG–AC
precursor is sensitive to water and stable to ethanol. Therefore, by
changing the ratio of water to ethanol, the nucleation and growth
rate of ZnO could be tuned. The function of organic structure-
directing agents is relative with their ability to selected adsorption
on certain crystal plane of ZnO, and to assemble ZnO crystals to
superstructures [29,30]. Therefore, ZnO morphology could be
easily regulated by changing the reaction parameters. As a particle
2
ꢀ
direct medium for forming ZnO should be Zn(OH)
4
. In present
work, we have performed serials experiments to study the
transformation process of Zn–EG–AC precursor into ZnO. The
reaction is too fast to be detailed monitored the phase change of
the Zn–EG–AC at the higher temperature. For example, phase-
pure ZnO are obtained at 100 8C for only 1 h. Therefore, the
hydrolysis of precursor was performed at lower reaction (70 8C)
to decrease the hydrolysis rate and to monitor the phase change
of Zn–EG–AC in the synthesis. As shown by XRD patterns shown
in Fig. 6, Zn–EG–AC gradually transforms into the ZnO within
the 8 h. At the initial step (1 h), no peaks of crystalline ZnO were

1
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C. Tian et al. / Materials Research Bulletin 46 (2011) 1283–1289
Fig. 5. SEM images of ZnO with different microstructures and their corresponding preparation parameters: (a) asymmetric hexagonal prism-like (R = 0, 100 8C, 5 h, 0.5 g
saccharose); (b) drum-like (R = 0, 100 8C, 5 h, 0.5 g starch); (c) twinned hexagonal plate-like (R = 0, 120 8C, 5 h, 0.5 g SDS); (d) twinned disk-like (R = 0, 100 8C, 5 h, 0.5 g SDS);
(e) hamburger-like (R = 19/1, 120 8C 15 h, 0.5 g SDS); (f) cauliflower-like 1 (R = 19/1, 120 8C, 10 h, 0.1 g SDS); (g) hoof-like (R = 19/1, 140 8C, 10 h, 1 g PVP); (h) cauliflower-like
2
(R = 19/1, 140 8C, 15 h, 1 g PVP); (i) acaleph-like (R = 19/1, 100 8C, 15 h, 0.1 g of PVP). The insets in each figure are corresponding high-magnification SEM image. The (a’–f’)
are particle size distribution corresponding to (a–f).
material, the specific surface area (SSA) is a very important
parameter. The SSA of typical samples was determined and the
results are listed in Table S1. From the results, we can see that the
specific surface area of all samples is relative small as no obvious
micro- or meso-pore in as-prepared samples. However, one can see
that the assemble structures composed of small particles (Fig. 5i)
and tube-like structure (Fig. 4b) have a higher BET specific surface
area than other single morphological particles generally. As
known, the higher BET specific surface area is important for
practical application of materials in certain areas. In our further
work, we will focus attention on preparing these kinds of materials
by elaborately tuning synthesis parameters.

C. Tian et al. / Materials Research Bulletin 46 (2011) 1283–1289
1289
Universities of Heilongjiang province of China (No. 1154G24),
Doctoral Research Foundation of Heilongjiang University and
Youth Science Foundation of Heilongjiang University (QL200711).
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.materresbull.2011.03.030.
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