Flower-like In2O3 hierarchical nanostructures: Synthesis, characterization, and gas sensing properties

Article abstract of DOI:10.1039/c4ra10497h

Hierarchical In₂O₃ nanostructures with flower-like morphology were synthesized by annealing In(OH)₃ precursors prepared via a one-step hydrothermal method using the mixed solution of N,N-dimethylformamide (DMF) and deionized water as solvent. The crystal structure and morphology of the obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N₂ adsorption-desorption analyses. The results revealed that the synthesized flower-like In₂O₃ hierarchical nanostructures were constructed from In₂O₃ nanoplates which connected with each other to form flower-like architecture. On the basis of experimental results, a possible mechanism for the formation of flower-like In₂O₃ hierarchical nanostructures was considered. Moreover, gas sensing investigation showed that the sensor based on flower-like In₂O₃ hierarchical nanostructures exhibited a superior response, good selectivity and stability to ethanol gas. The enhancement in gas sensing properties was attributed to their unique structure, large surface areas, and more surface active sites. This journal is

Full text of DOI:10.1039/c4ra10497h

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Flower-like In O hierarchical nanostructures:
2
3
synthesis, characterization, and gas sensing
properties
Cite this: RSC Adv., 2014, 4, 50241
Dan Han, Peng Song,* Huihui Zhang, Huihui Yan, Qi Xu, Zhongxi Yang and Qi Wang*
Hierarchical In
O
2 3
nanostructures with flower-like morphology were synthesized by annealing In(OH)
3
precursors prepared via
a
one-step hydrothermal method using the mixed solution of N,N-
dimethylformamide (DMF) and deionized water as solvent. The crystal structure and morphology of the
obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM),
transmission electron microscopy (TEM), and N
that the synthesized flower-like In hierarchical nanostructures were constructed from In
nanoplates which connected with each other to form flower-like architecture. On the basis of
experimental results, possible mechanism for the formation of flower-like In hierarchical
nanostructures was considered. Moreover, gas sensing investigation showed that the sensor based on
flower-like In hierarchical nanostructures exhibited a superior response, good selectivity and stability
2
adsorption–desorption analyses. The results revealed
2
O
3
2 3
O
a
2 3
O
Received 15th September 2014
Accepted 30th September 2014
2 3
O
DOI: 10.1039/c4ra10497h
to ethanol gas. The enhancement in gas sensing properties was attributed to their unique structure, large
surface areas, and more surface active sites.
www.rsc.org/advances
research and the development of novel devices. To meet the
demand for practical applications, various In O nano-
Introduction
2
3
16
Ethanol sensing has been widely applied in various elds, such structures have been fabricated, including nanoparticles,
17
18
as in ethanol breath analyzers for detecting ethanol vapor in nanowires and nanorods, nanoplates or nanosheets, and 3D
19,20
drivers' breath, in foodstuffs experiments to assess the devel- hierarchitectures.
Being a special kind of nanostructure, 3D
opment of bacteria and fungi in food, in monitoring the hierarchical nanostructures have become strategic for various
biomedical and chemical processes in chemical industries and applications mainly due to their large specic surface area and
1–3
so on. Thus, growing concern about air pollution with respect desirable surface permeability. Actually, these favorable prop-
to public health has enhanced the demand for gas sensors for erties are also signicant for gas sensing, which can allow fast
monitoring ethanol concentration in the environment. Metal diffusion for target gases to interact with the entire sensing
oxide semiconductor gas sensors have attracted much attention layer. To date, much effort has been given to prepare the 3D
for their diverse applications in ethanol detection. Until now, a hierarchical In
O
structures by many synthetic strategies. For
these approaches, the hydrothermal synthesis method has been
LaFeO , and WO (ref. 7) have been successfully obtained. As proved to an effective technique, which has the obvious
2
3
4
5
2
number of ethanol-sensing sensors based on SnO , ZnO,
6
3
3
21,22
an important n-type semiconductor, indium oxide (In O ) with advantages of simple, mild, and high yields.
In our previous
nanospheres consisted of numerous tiny
nanoparticles were synthesized by hydrothermal
2 3
O
-based sensors have been investigated for the detection of synthesis method, which exhibited higher response to ethanol
2
3
2 3
high chemical and thermal stability has attracted considerable work, 3D porous In O
8–11
research efforts in its applicability as gas sensors.
In
ethanol vapor at various concentration levels.
As we known, the crystal phase, morphologies, as well as the Hence, it is strongly desirable for the fabrication of the porous
porosity have a profound inuence on the sensing performance In hierarchical nanostructures by exploring more simple
2 3
Recently, In O
12–15
23
gas compared with that of commercial bulk In O particles.
2 3
2 3
O
of In O3 nanomaterials. Therefore, the design and tailor of and effective techniques. However, despite this recent progress,
2
In O nanomaterials with different morphologies and struc- there are still some difficulties in the organization of 2D
2
3
tures are very important in view of both basic fundamental building blocks (e.g. nanosheets or nanoplates) into 3D super-
structures, especially when they need to be porous and thus
possess a high surface area.
It is also noted that additive-free synthesis of nanostructures
and self-assembling them into well-dened structures remains
School of Material Science and Engineering, Shandong Provincial Key Laboratory of
Preparation and Measurement of Building Materials, University of Jinan, Jinan
2
5
50022, China. E-mail: mse_songp@ujn.edu.cn; mse_wangq@ujn.edu.cn; Fax: +86
31 87974453; Tel: +86 531 82765473
a huge challenge. Herein we report a successful facile self-
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 50241–50248 | 50241

View Article Online
RSC Advances
Paper
assembly, template and additive-free synthesis route toward alloy coil through the tube as a heater to operating the
achieving ower-like In O hierarchical nanostructures con- temperature. Aer dried in the air and aged at aging set at 2
2
3
sisted of In O nanoplates via an oriented attachment growth days, it has been an indirectly-heated gas sensor, and then the
2
3
mechanism. The synthesis entails preparation of the interme- gas sensor was put into the test chamber in a measuring system
diate In(OH) precursors under hydrothermal conditions using of WS-30A (Winsen Electronics Co. Ltd., Zhengzhou, China) by a
InCl as a precursor, a mixed solvent system of water and N,N- static process.
3
24,25
3
Then, the sensors were put into a glass
dimethylformamide (water/DMF) as the reaction medium. The chamber at the beginning. When the resistances of all the
products were characterized by FESEM, TEM, and nitrogen sensors were stable, the calculated amount of the target gas or
sorption. According to the experimental results, a possible liquid was injected into glass chamber by a micro-injector and
formation mechanism was proposed and its ethanol sensing mixed with air. Aer the sensor resistances reached a new
properties were investigated.
constant value, the test chamber was opened to recover the
sensors in air. All the measurements were performed in a
laboratory fume hood with a large draught capacity. The sensor
resistance and response values were acquired by the analysis
system automatically. The whole experiment process was per-
Experimental
Synthesis of ower-like In O hierarchical nanostructures
2
3
In the experiments, all the chemical regents were analytical formed in a super-clean room with the constant humidity and
grade and used without further purication. In a typical temperature. In the test process, a working voltage of 5 V
experiment, 0.5 mmol InCl $4H O was rst dissolved in the (Vworking) was applied. By monitoring the voltage across the
3
2
mixed solution of 15 mL distilled water and 15 mL DMF at room reference resistor (Voutput), the response of the sensor in air or in
temperature, followed by addition of 1 mmol Na $2H
a test gas could be measured. The sensor response was dened
3
C
6
H
5
O
7
2
O
under vigorous stirring. Subsequently, 2 mmol of urea was as,
added into the above mixed solution under vigorous stirring.
The reaction mixture was transferred into a Teon-lined stain-
Response ¼ Rair/Rgas
(1)
ꢀ
less-steel autoclave and kept at 170 C for 14 h. Aer the
where Rair is the resistance of the sensor in air and Rgas is the
resistance of sensor in the presence of the test gas. Then, the
slope coefficient of response value to the logarithm of the
concentration was dened as sensitivity. The response and
recovery time was dened as the time taken by the sensors to
achieve 90% of the total resistance change in the case of
adsorption and desorption, respectively.
hydrothermal procedure, the autoclave cooled naturally down
to room temperature. The precipitates were collected by
centrifugation, washed several times with deionized water and
ꢀ
ethanol, respectively, and dried at 60 C for 12 h. Finally, ower-
like In
2
O
3
hierarchical nanostructures were obtained by
ꢀ
annealing the precipitates at 500 C for 3 h in air atmosphere.
Characterization
The crystal structure and phase composition of samples were
identied by the means of X-ray diffraction (XRD, Bruker D8
Advance) using CuKa1 radiation (l ¼ 0.15406 nm) at 30 kV and
Results and discussion
Crystal structure and morphology
ꢀ
ꢁ1
ꢀ
4
8
0 mA at a scanning rate of 2 at 2q min ranging from 20 to
ꢀ
The crystal structure of the prepared samples was characterized
by X-ray diffractometer. As shown in Fig. 1, the diffraction peaks
of the precursor (curve a) are in good agreement with cubic
structure In(OH)3 (JCPDS no. 73-1810), no peaks for other
impurities are detected. Aer annealing at 500 C, all the peaks
of the sample (curve b) are indexed to the hexagonal phase of
0 , and energy dispersive X-ray spectroscopy, the morphology
and the microstructure of the products were characterized by
eld emission gun scanning electron microscope (FESEM,

Hitachi S4800), transmission electron microscopy (TEM, Hita-
chi H-800) and high resolution electron microscopy (HRTEM,
JEOL 2010). The specic surface area was estimated using the
ꢀ
In
other phases were observed, conrming the precursor has
completely transformed into the pure hexagonal In crystal.
Compared with those of the bulk material, the peaks were
relatively broadened, which demonstrated that the In had a
2 3
O with the standard date le (JCPDS le no. 22-0336). No
Brunauer–Emmett–Teller (BET) method based on the N
2
adsorption–desorption tests. Pore-size distribution was calcu-
lated from the adsorption branch of the nitrogen isotherm,
using the Barrett–Joyner–Halenda method applied to the
desorption part of the adsorption–desorption isotherm.
2 3
O
2 3
O
small crystal size. Further, the crystallite size is estimated using
the Scherrer formula:
Gas sensor fabrication and response tests
The fabrication progress of the gas sensor was as follows: the as-
obtained nal product was ground and mixed with deionized
D ¼ 0.89l/b cos q
(2)
water in order to form paste in agate mortar, which was evenly where D is the mean crystallite size, l is the wavelength of the X-
smeared onto the outer surface of a ceramic tube by hair brush ray radiation (l ¼ 0.154 nm for CuKa1 radiation), and b is the
to form a thick lm to cover a pair of Au electrode, which had full width at half-maximum of diffraction peak at 2q. The
been printed on the tube previously. Four Pt lead wires attach- average crystallite size of the as-prepared In O sample was
2 3
ing to the Au electrodes were used for measurement and a Ni–Cr approximately 18.2 nm.
50242 | RSC Adv., 2014, 4, 50241–50248
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
Fig. 3 (a) FESEM image of the In
like In
of flower-like In
2
O
3
sample; (b) EDS pattern of flower-
2
O
3
nanostructure; (c) low and (d) high magnification TEM image
hierarchical nanostructure; (e) the corresponding
2 3
O
3
Fig. 1 XRD patterns of the In(OH) precursors and as-synthesized
In O products.
2 3
HRTEM image with labeled lattice spacing.
about 0.274 nm, in agreement with the (110) plane of hexagonal
phase of In O , demonstrating the nanoplates were mainly
2 3
dominated by the (110) surface.
To further obtain the information about the pores in the
nanoplates, the nitrogen adsorption and desorption measure-
ments were performed at 77 K. Seen from Fig. 4, the prepared
The morphology of as-prepared In(OH)
3
precursor was
demonstrated by FESEM, as shown in Fig. 2. It can be seen that
the sample was composed of a large number of ower-like
architecture with diameters of about 1.5–2 mm (Fig. 2(a)).
Furthermore, the 3D ower-like architecture was consisted of
many 2D nanoplates of In(OH) (Fig. 2(b)). In O sample can be
3
2 3
2 3
In O products exhibited a hysteresis loop in a high relative
ꢀ
obtained by annealing the In(OH) precursor at 500 C. Clearly
3
pressure range of 0.63–0.94, which was ascribed to a type IV
isotherm, indicating the presence of mesopores. The pore size
distribution (inserted in Fig. 4) for the desorption branch of the
2 3
the In O product inherits the morphology of its precursor, as
shown in Fig. 3(a). The detailed structure characteristics of
them have been described previously. Composition of the as-
N
2
isotherm using the BJH method indicates that ower-like
2 3
prepared ower-like In O hierarchical nanostructures is shown
In O hierarchical nanostructures have an average pore diam-
2 3
in Fig. 3(b). It is revealed that the sample is composed of In and
O elements. Moreover, no impurity was detected, indicating a
high purity of the as-prepared products. Fig. 3(c) shows the
eter of 18 nm. The result is in good agreement with the TEM
image. Since the as-prepared In O products possess large
2
3
2 3
representative TEM image of a single ower-like In O nano-
structure. It can be seen that the ower-like nanostructure with
the diameter of 1.5–2 mm, which is built of a lot of nanoplates.
Fig. 3(d) shows that nanoplates of ower-like nanostructures
possess a porous structure with a pore-size distribution ranging
form 10 to 20 nm. The HRTEM image of a nanoplate at the edge
of the ower-like In O nanostructure is depicted in Fig. 3(e).
2
3
The observed lattice perpendicular to the nanoplates length is
Fig. 4 Typical N
Fig. 2 (a) Low and (b) high magnification FESEM images of the as- distribution plots (inset) of flower-like In
prepared In(OH) precursors. nanostructures.
2
adsorption–desorption isotherm and BJH pore size
2
O
3
hierarchical
3
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 50241–50248 | 50243

View Article Online
RSC Advances
Paper
surface area and mesoporous structure, which are greatly
The oriented growth into In(OH)
3
nanoplates is possibly
advantageous for gas adsorption–desorption, gas molecular induced by the reorientation of the formed In(OH) aggregation
3
diffusion, and providing more surface sites for oxygen, it is composed of numerous nuclei, under the present of DMF, in
believed that they can be potentially applied in gas sensors with order to minimize the total energy of the reaction system. A
enhanced gas-sensing performance.
similar phenomenon has been reported in the formation of
29
Based on the above experimental results, we proposed a ower-shaped SnO
2
nanostructures. Previous reports sug-
possible formation mechanism for ower-like In
chical nanostructures. It was believed that the formation of the products morphology.
products could be brought out as the following equations. during the growth process of ower-like hierarchical nano-
2 3
O hierar- gested that the solvent composition has a signicant impact on
30,31
To reveal the inuence of DMF
3
+
3ꢁ
Firstly, In and [C H O ]
are produced aer InCl3 and structures, the study of morphology evolution of In(OH)3
6
5
7
Na C H O $2H O dissolved into the deionized water (eqn (3) precursor with different reaction conditions was investigated by
3
6
5
7
2
3
+
3ꢁ
7
and (4)). In can be easily combined with [C H O ] via the changing the H O–DMF volume ratios, while temperature and
chelating effect (eqn (5)). Urea is an important biological reaction time were kept at 170 C and 14 h, respectively. As
molecule that can decompose and release OH in an indirect shown in Fig. 6(a) and (b), unconsolidated spheres and particles
manner (eqn (6) and (7)). Then, In will be released and grad- were observed with the H
ually converted into In(OH) nuclei via the chemical reaction 20 : 10. When the products were prepared at a volume ratio of
eqn (8)). Upon hydrothermal treatment, the In(OH) nuclei 15 : 15, considerable ower-like hierarchical nanostructures
6
5
2
ꢀ
ꢁ
3
+
2
O–DMF volume ratio of 30 : 0 and
3
(
3
subsequently aggregated to form small particles, followed by were obtained (Fig. 6(c)). As the sample prepared at volume ratio
their self-assembly into 2D In(OH)3 nanoplates through of 10 : 20, FESEM image (Fig. 6(d)) showed that In(OH)3
oriented growth, and then the arrangement of these nanoplates precursor transformed into the sphere-like architecture with
2
6–28
into 3D hierarchical nanostructures,
trated in Fig. 5. Finally, during the calcination process, the the spheres. When the H
In(OH) precursor is converted to In (eqn (9)). Thermal product was observed due to the absence of water (eqn (6)).
decomposition of the organic impurity (citrate salt) and the FESEM images under different solvent ratios indicated that the
release of H O in conned space during the sintered process led solvent composition had a signicant inuence on the
to the formation of porous structure.
as schematically illus- diameters of 1 mm, only few plates were detected at the edge of
2
O–DMF volume ratio was 0 : 30, no
3
2 3
O
2
morphologies. And the detailed mechanism for the formation
of ower-like In O hierarchical nanostructures is still under
investigation by our group.
2
3
3
+
ꢁ
InCl
3
/ In + 3Cl
(3)
(4)
3
ꢁ
+ 3Na
+
Na
3
C
6
O
7
H
5
/ [C
6
H
5
O
7
]
Gas-sensing properties
3
+
3ꢁ
3ꢁ 3+
7
In + [C H O ] / [C H O ] In
(5) In general, the response of semiconducting metal oxide gas
32
6
5
7
6
5
sensors was dependent on the operating temperature. There-
CO(NH
2
)
2
+ 3H
2
O / CO
2
+ 2NH
3
$H
2
O
(6) fore, to nd the optimum detection temperature, the responses
2 3
of ower-like In O hierarchical nanostructures to 100 ppm
+
ꢁ
NH $H O / NH + OH
(7)
(8)
(9)
3
2
4
3ꢁ
3+
ꢁ
3ꢁ
5
H ]
[C
6
O
H
7 5
]
In + 3OH / In(OH)
3
+ [C
6
O
7
In(OH) / In + H O
3
2
O
3
2
Fig. 6 FESEM images of In(OH)
O–DMF volume ratio of (a) 30 : 0; (b) 20 : 10; (c) 15 : 15 and (d)
10 : 20.
3
precursors prepared with different
Fig. 5 Schematic illustration of the formation process of flower-like
In hierarchical nanostructures.
H
2
2 3
O
50244 | RSC Adv., 2014, 4, 50241–50248
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
2
ꢁ
ꢁ
ethanol were tested as a function of operating temperature from to form active O and O . This phenomenon continues up to a
ꢀ
2
00 to 400 C. As shown in Fig. 7, the response was strongly certain optimum temperature, beyond which exothermic gas
dependent on the operating temperature. As the working adsorption becomes difficult and gas molecules begin to
temperature increases, a higher response is obtained because of desorption in large quantities, leading to a drop in sensor
the activation of adsorbed molecular oxygen and lattice oxygen response. Thus, the optimum temperature is a balance point
3
3,34
between two conicting mechanisms.
It can be seen that the
ꢀ
sensor had an optimum operating temperature of 320 C, at
which the sensor exhibited the highest response of 28 to
ethanol gas. As a consequence, we choose 320 C as the
ꢀ
optimum operating temperature to proceed with subsequent
investigation in our experiment.
Fig. 8(a) shows the typical response of gas sensors based on

ower-like In
ethanol at 320 C. For the gas sensing mechanism of as-
prepared ower-like In hierarchical nanostructures, it
2 3
O hierarchical nanostructures to 2–1000 ppm
ꢀ
2 3
O
should belong to the surface-controlled type, which may be
explained by the change in resistance of the sensor upon
exposure to different gas atmospheres. When the sensors were
exposed to air, O adsorb on the surface and create chemisorbed
2
ꢁ
ꢁ
2ꢁ
oxygen species (such as O2 , O and O ) by capturing electrons
from the conductance band through eqn (10), resulting in a
high resistance state of the In
2
O
3
samples:
2 3
Fig. 7 Response vs. operating temperature of flower-like In O hier-
archical nanostructures exposing 100 ppm ethanol.
O
2
(gas) / O
2
(ads)
(10)
Fig. 8 (a) Typical response curves and variation of the response of
2 3
flower-like In hierarchical nanostructures exposed to different Fig. 9 (a) Reproducibility (3 cycles) and (b) stability of flower-like In O
2
O
3
concentration of ethanol ranging from 2 to 1000 ppm and measured hierarchical nanostructures sensor on successive exposure to 100
ꢀ
ꢀ
at 320 C; (b) the corresponding log(S ꢁ 1) vs. log(C).
ppm ethanol at 320 C.
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 50241–50248 | 50245

View Article Online
RSC Advances
Paper
ꢁ
ꢁ
O (ads) + e / O2 (ads)
(11) based on ower-like In
2
O
3
hierarchical nanostructures has a
2
good linear relationship with the ethanol concentration (2–1000
(12) ppm range) in logarithmic forms, and the value of b towards
2ꢁ
ꢁ
ꢁ
O
(ads) + e / 2O (ads)
ethanol was about 0.5704, which was in good agreement with
ꢁ
ꢁ
2ꢁ
O
(ads) + e / O (ads)
(13)
37,38
the theory of power laws for semiconductor sensors.
results highlighted the potential applications of the ower-like
In hierarchical nanostructures in monitoring ethanol gas.
It is evident that the response curves of the sensor increases
The
2 3
O
When the sensors exposed to ethanol vapor at higher
temperature, ethanol reacts with the adsorbed oxygen ions
reducing their concentration and thereby increasing the semi-
conductor conductivity. The possible reactions took place on
sharply with increasing concentration of ethanol and then
returns to the baseline quickly with the ethanol exhausted out
in the closed testing chamber, indicating their quick and
reversible response and recovery time. For 100 ppm ethanol gas,
18 s and 9 s are the response and recovery time for ower-like
35,36
the surface of indium oxide as follows:
2
ads
ꢁ
ꢁ
/ 2CO + 3H O + 6e
CH CH OH + 3O
3
(14)
2
2
2
In
2
O
3
hierarchical nanostructures, respectively. In addition, the
hierarchical nanostructures based sensor

ower-like In O
2 3
When exposed to air again, the In O sensors recover to the
2 3
exhibits excellent reproducibility as shown in Fig. 9(a). The
sensor maintained its initial response amplitude without a clear
decrease upon three successive sensing tests for 100 ppm
ethanol. Furthermore, the stability of the sensor was also
determined at optimal operating temperature for 60 hours.
Clearly, as shown in Fig. 9(b), the senor has nearly constant
response to 100 ppm ethanol, which conrmed the high
initial electronic structure. With increasing concentration of
ethanol, the sensor response greatly increased. The response
b
can be empirically represented as S ¼ a[C] + 1, where a and b
are the constants and S is the gas response, C is the concen-
tration of the test gas. Generally, the exponent b has an ideal
value of either 0.5 or 1. Fig. 8(b) shows a chart of logarithm of
the response of the sensor (Sꢁ1) versus the logarithm of ethanol
concentration (C). It can be seen that the response of the sensor
2 3
stability of the sensor based on ower-like In O hierarchical
nanostructures.
A comparative gas sensing study between the as-prepared
products and commercial bulk In O particles prepared by
2
3
precipitation method was performed to demonstrate the supe-
rior ethanol-sensing properties of ower-like In O hierarchical
2
3
nanostructures. We have measured the response of ower-like
In hierarchical nanostructures and bulk In particles to
2
O
3
2 3
O
six kinds of volatile vapors with a concentration of 50 ppm, such
as ammonia, benzene, acetone, methanol, formaldehyde and
ꢀ
ethanol at the working temperature of 320 C (Fig. 10). As
expected, the sensor based on ower-like In O hierarchical
2
3
nanostructures exhibited enhanced responses for each gas
compared with that based on bulk In O particles. Furthermore,
2
3
2 3
the response of sensor based on ower-like In O hierarchical
nanostructures to ethanol was apparently higher than that to
other gases, which seems to depend on the interaction
discrepancy between the sensing layer and different testing gas.
2 3
Fig. 10 Responses of flower-like In O hierarchical nanostructures
Furthermore, the response performances of some typical In
2 3
O -
and bulk particles upon exposure to six kinds of target gases (50 ppm)
based ethanol gas sensors were listed in Table 1. It should be
ꢀ
at a working temperature of 320 C.
2 3
Table 1 Gas-sensing properties of various In O nanostructures to 100 ppm ethanol in the literatures and present study
Operating temperature
( C)
Sensor
response
Response/recovery
times (s)
Detection limit
(ppm)
ꢀ
Sensing In
2
O
3
nanostructures
Ref.
Flower-like In
In :Er hollow spheres
Nanoporous In hollow spheres
In nanospheres
Co-doped In nanowires
In porous nanoparticles
Mesoporous In
Au-loaded In
In microspheres
2
O
3
nanostructures
320
215
400
275
300
200
220
140
200
27.6
40.3
137.2
ꢂ21
ꢂ17
ꢂ4
18/9
2
7
20
20
5
100
0.05
10
This work
2
O
3
10/23
2/830
16/24
2/3
39
40
23
41
42
43
44
45
2
O
3
2
O
3
2
O
3
2
O
3
6/15
2
O
3
27.9
6.5
74/119
12/24
27/24
2 3
O nanobers
2
O
3
1.8
100
50246 | RSC Adv., 2014, 4, 50241–50248
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
pointed out that ower-like In
2
O
3
hierarchical nanostructures 12 A. Ayeshamariam, M. Bououdina and C. Sanjeeviraja, Mater.
in present study possess superior performance when compared
Sci. Semicond. Process., 2013, 16, 686–695.
with other nanostructured In O sensors reported in previous 13 Z. L. Zhan, J. W. Lu, W. H. Song, D. G. Jiang and J. Q. Xu,
2
3
works. Consequently, it was concluded that the sensor based on
the as-prepared ower-like In hierarchical nanostructures 14 M. I. Ivanovskaya, D. A. Kotsikaua, A. Taurinob and
showed superior gas sensing performance towards ethanol and P. Siciliano, Sens. Actuators, B, 2007, 124, 133–142.
it may be have potential applications in the detection of ethanol 15 H. Ko, S. Park, S. An and C. Lee, Curr. Appl. Phys., 2013, 13,
Mater. Res. Bull., 2007, 42, 228–235.
2 3
O
vapors.
919–924.
16 K. Inyawilert, A. Wisitsora-at, A. Tuantranont, P. Singjai,
S. Phanichphant and C. Liewhiran, Sens. Actuators, B, 2014,
Conclusions
192, 745–754.
1
1
1
2
7 C. W. Lai, J. Y. Dai, X. Y. Zhang, H. L. W. Chan, Y. M. Xu, Q. Li
and H. C. Ong, J. Cryst. Growth, 2005, 282, 383–388.
8 D. L. Shao, L. Q. Qin and S. Sawyer, Appl. Surf. Sci., 2012, 261,
In summary, a simple one-step solution route combined with a
subsequent calcining process was reported for the formation of

ower-like In O3 hierarchical nanostructures, which were
2
123–127.
composed of many 2-D nanoplates with high porosity. The
structure and morphology of In samples were investigated in
9 Q. Qi, P. P. Wang, J. Zhao, L. L. Feng, L. J. Zhou, R. F. Xuan,
Y. P. Liu and G. D. Li, Sens. Actuators, B, 2014, 194, 440–446.
0 A. Vomiero, S. Bianchi, E. Comini, G. Faglia, M. Ferroni,
N. Poli and G. Sberveglieri, Thin Solid Films, 2007, 515,
2 3
O
detail, and a possible growth mechanism was supposed from
the viewpoint of nucleation and self-assembly of building
blocks. Moreover, the gas sensing tests exhibited that ower-
like In O hierarchical nanostructures showed superior gas
2 3
sensing performance towards ethanol. The results suggest that
8356–8359.
2
2
2
2
2
2
2
1 W. Zeng, H. Zhang, Y. Q. Lia, W. G. Chen and Z. C. Wang,
Mater. Res. Bull., 2014, 57, 91–96.
2 P. Sun, W. Zhao, Y. Cao, Y. Guan, Y. F. Sun and G. Y. Lu,
CrystEngComm, 2011, 13, 3718–3724.
3 P. Song, D. Han, H. H. Zhang, J. Li, Z. X. Yang and Q. Wang,
Sens. Actuators, B, 2014, 196, 434–439.
4 N. F. Hamedani, A. R. Mahjoub, A. A. khodadadi and
Y. Mortazavi, Sens. Actuators, B, 2012, 169, 67–73.
5 J. R. Huang, K. Yua, C. P. Gu, M. H. Zhai, Y. Z. Wu, M. Yang
and J. H. Liu, Sens. Actuators, B, 2010, 147, 467–474.
6 J. Y. Liu, T. Luo, F. L. Meng, K. Qian, Y. T. Wan and J. H. Liu,
J. Phys. Chem. C, 2010, 114, 4887–4894.
the as-prepared ower-like In O hierarchical nanostructures
2
3
are promising candidates for good performance ethanol sensor.
Acknowledgements
This work was nancially supported by National Natural
Science Foundation of China (no. 61102006), Natural Science
Foundation of Shandong Province, China (no. ZR2010EQ009).
Notes and references
7 J. T. Zai, J. Zhu, R. R. Qi and X. F. Qian, J. Mater. Chem. A,
2013, 1, 735–745.
1
G. Neri, A. Bonavita, G. Micali, N. Donato, F. A. Deorsola,
P. Mossino, I. Amato and B. De Benedetti, Sens. Actuators, 28 C. Q. Wang, D. R. Chen and X. L. Jiao, J. Phys. Chem. C, 2009,
B, 2006, 117, 196–204.
113, 7714–7718.
P. Ivanov, E. Llobet, X. Vilanova, J. Brezmes, J. Hubalek and 29 W. L. Jiao and L. Zhang, Particuology, 2013, 11, 743–747.
2
3
4
5
6
7
8
X. Correig, Sens. Actuators, B, 2004, 99, 201–206.
L. Li, M. M. Liu, S. J. He and W. Chen, Anal. Chem., 2014, 86,
30 T. Yan, X. Wang, J. Long, H. Lin, R. Yuan, W. Dai, Z. Li and
X. Fu, New J. Chem., 2008, 32, 1843–1846.
7
996–8002.
31 B. L. Tao, Y. Zhang, D. Z. Han, Y. P. Li and Z. F. Yan, J. Mater.
Chem. A, 2014, 2, 5455–5461.
32 Z. Lou, L. L. Wang, T. Fei and T. Zhang, New J. Chem., 2012,
36, 1003–1007.
P. P. Jin, X. X. Zou, L. J. Zhou, J. Zhao, H. Chen, Y. Tian and
G. D. Li, Sens. Actuators, B, 2014, 104, 142–148.
J. Xie, H. Wang and M. Duan, Sens. Actuators, B, 2014, 203,
2
39–244.
33 L. J. Bie, X. N. Yan, J. Yin, Y. Q. Duan and Z. H. Yuan, Sens.
Actuators, B, 2007, 126, 604–608.
34 P. Sun, X. Zhou, C. Wang, K. Shimanoe, G. Lu and
N. Yamazoe, J. Mater. Chem. A, 2014, 2, 1302–1308.
35 J. Q. Xu, J. J. Han, Y. Zhang, Y. A. Sun and B. Xie, Sens.
Actuators, B, 2008, 132, 334–339.
X. F. Chu, S. M. Zhou, W. B. Zhang and H. F. Shui, Mater. Sci.
Eng., B, 2009, 164, 65–69.
S. B. Upadhyay, R. K. Mishra and P. P. Sahay, Sens. Actuators,
B, 2014, 193, 19–27.
P. Sowti Khiabani, A. Hosseinmardi, E. Marzbanrad,
S. Ghashghaiea, C. Zamanic, M. Keyanpour-Radd and 36 H. Men, P. Gao, B. B. Zhou, Y. J. Chen, C. L. Zhu, G. Xiao,
B. Raissi, Sens. Actuators, B, 2012, 162, 102–107.
P. Sowti Khiabani, E. Marzbanrad, C. Zamani, R. Riahifar
and B. Raissi, Sens. Actuators, B, 2012, 166–167, 128–134.
0 T. Wagner, T. Sauerwald, C.-D. Kohl, T. Waitz, C. Weidmann
and M. Tiemann, Thin Solid Films, 2009, 517, 6170–6175.
1 P. Y. Song and W. D. Zhang, Mater. Res. Bull., 2014, 53, 177–
L. Q. Wang and M. L. Zhang, Chem. Commun., 2010, 46,
7581–7583.
37 N. Yamazoe and K. Shimanoe, Sens. Actuators, B, 2008, 128,
566–573.
38 X. J. Liu, Z. Chang, L. Luo, X. D. Lei, J. F. Liu and X. M. Sun, J.
Mater. Chem., 2012, 22, 7232–7238.
9
1
1
184.
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 50241–50248 | 50247

View Article Online
RSC Advances
Paper
3
9 T. Zhang, F. B. Gu, D. M. Han, Z. H. Wang and G. S. Guo, 43 X. H. Sun, H. R. Hao, H. M. Ji, X. L. Li, S. Cai and
Sens. Actuators, B, 2013, 177, 1180–1188. C. M. Zheng, ACS Appl. Mater. Interfaces, 2014, 6, 401–409.
0 S. J. Kim, I. S. Hwang, J. K. Choi, Y. C. Kang and J. H. Lee, 44 X. J. Xu, H. T. Fan, Y. T. Liu, L. J. Wang and T. Zhang, Sens.
4
Sens. Actuators, B, 2011, 155, 512–518.
Actuators, B, 2011, 160, 713–719.
4
4
1 Z. Li and Y. Dzenis, Talanta, 2011, 85, 82–85.
2 L. Wang, F. Tang, K. Ozawa, Z. G. Chen, A. Mukherj, Y. Zhu,
J. Zou, H. M. Cheng and G. Q. Lu, Angew. Chem., Int. Ed.,
45 X. Q. Wang, M. F. Zhang, J. Y. Liu, T. Luo and Y. T. Qian,
Sens. Actuators, B, 2009, 137, 103–110.
2009, 48, 7048–7051.
50248 | RSC Adv., 2014, 4, 50241–50248
This journal is © The Royal Society of Chemistry 2014