Improved NO
2
sensing properties at low temperature using reduced
graphene oxide nanosheeteIn
2
O
3
heterojunction nanofibers
Chao Yan
a
, Hongbing Lu
a, *
, Jianzhi Gao
a, **
, Ying Zhang
b
, Quanmin Guo
c
,
Haoxuan Ding
c
, Yitao Wang
c
, Fenfen Wei
a
, Gangqiang Zhu
a
, Zhibo Yang
a
,
Chunlan Wang
d
a
School of Physics and Information Technology, Shaanxi Normal University, Xi'an 710062, China
b
Engineering University of PAP, Xi'an 710086, China
c
School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, United Kingdom
d
School of Science, Xi'an Polytechnic University, Xi'an 710048, China
article info
Article history:
Received 9 October 2017
Received in revised form
13 January 2018
Accepted 15 January 2018
Keywords:
In
2
O
3
Reduced graphene oxide
Electrospinning
pen junctions
Gas sensor
abstract
Pure In
2
O
3
and reduced graphene oxide (rGO)eIn
2
O
3
composite nanofibers are prepared by a facile
electrospinning technique. Low-temperature gas-sensing properties to NO
2
of the produced nanofibers
are evaluated. Our results indicate that in comparison with pure In
2
O
3
nanofibers, the rGOeIn
2
O
3
het-
erojunction nanofibers display much better sensing properties in response, selectivity and detection limit
to NO
2
. Moreover, the weight ratios of rGO to In
2
O
3
are used as a parameter to estimate the best gas-
sensing properties of rGOeIn
2
O
3
nanofibers. Consequently, the heterojunction nanofibers with an
optimized amount of rGO (2.2 wt%) exhibit the highest response of 42 to 5 ppm NO
2
at the low operating
temperature of 50
C, which is 4.4 times higher than that of pristine In
2
O
3
. From our perspective, the
enhanced sensing properties of the composite nanofibers can be mainly attributed to the formation of p
en heterojunctions between rGO and In
2
O
3
, and ultrahigh specific surface area as well as strong gas
adsorption capacity of rGO nanosheets. These excellent gas-sensing properties make the rGOeIn
2
O
3
heterojunction nanofibers attractive to application for low-temperature NO
2
gas sensors.
© 2018 Elsevier B.V. All rights reserved.
1. Introduction
Modern industry and technologies have greatly improved the
living standard of the human society. However, modern technolo-
gies also bring the side effects to our daily life, such as the non-
standard emission of the fossil fuel and automobile exhaust,
which have led to serious air pollution issues which affect our daily
life. Sensor technology plays a major role in toxic gas detection,
environmental monitoring and health care [1e5]. Among various
toxic gases, NO
2
, which can be easily produced via combustion
processes [6e8], is one of the major agents to cause acid rain and
smog. In addition, NO
2
is also harmful to human's respiratory sys-
tem. Therefore, detection of NO
2
gases with high and fast response
in our living and working environments is an important demand
for the future green world. During recent years, more and more
scientific researchers have devoted themselves to the development
of NO
2
gas sensors with high performances. Many different types of
materials have been investigated for working as NO
2
gas sensors,
such as SnO
2
[9e11], ZnO [12, 13], WO
3
[14e16], TiO
2
[17 , 18], Fe
2
O
3
[19,20] and In
2
O
3
[4,21e23].
Among the materials investigated, In
2
O
3
is one of the most
traditional and promising sensing materials and has attracted many
researchers' attention. As we know, composite nanostructures can
provide excellent opportunities to enhance the performances of the
materials [24e29]. Much effort has thus been made to improve the
sensing performances of In
2
O
3
by using In
2
O
3
-based composites,
such as surface modification with noble metals [29,30] and for-
mation of heterojunctions by adding other types of metal oxides
[31 ,32]. These heterojunctions are usually composed of different
materials with unequal band gaps, so that there is a difference in
Fermi energies between the two materials [33,34]. This difference
in Fermi energies will result in the transferring of electrons from a
high energy to the unoccupied lower energy states until the Fermi
energies are equilibrated. This process leads to the generation of a
* Corresponding author.
** Corresponding author.
E-mail addresses: hblu@snnu.edu.cn (H. Lu), jianzhigao@snnu.edu.cn (J. Gao).
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: http://www.elsevier.com/locate/jalcom
https://doi.org/10.1016/j.jallcom.2018.01.209
0925-8388/© 2018 Elsevier B.V. All rights reserved.
Journal of Alloys and Compounds 741 (2018) 908e917