MINISTRY OF EDUCATION AND TRAINING
HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGY
Nguyen Van Hoang
ELECTROSPINNING OF α-Fe2O3 AND ZnFe2O4
NANOFIBERS LOADED WITH REDUCED GRAPHENE
OXIDE (RGO) FOR H2S GAS SENSING APPLICATION
Major: Materials Science
Code: 9440122
ABSTRACT OF DOCTORAL DISSERTATION
OF MATERIALS SCIENCE
Hanoi - 2020
The Dissertation was completed at:
Hanoi University of Science and Technology
Supervisor: Prof. PhD. Nguyen Van Hieu
Reviewer 1:
Reviewer 2:
Reviewer 3:
The dissertation will be defended at the University Council of
Doctoral dissertation held at Hanoi University of Science and
Technology.
At ……….., date………..month…......year………..
The dissertation can be found at the libraries:
1. Ta Quang Buu, Hanoi University of Science and Technology
2. Vietnam National Library
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INTRODUCTION
1. Background of the thesis
Recently, 1D nanostructures including nanowires (NWs),
nanorods (NRs), nanotubes (NTs), and nanofibers (NFs) have
attracted much attention for a wide application including optical
catalysis, electronic devices, optoelectronic devices, storage devices,
and gas sensors due to their high surface-to-volume ratio. Especially,
NFs are widely used in many fields such as catalysis, sensor, and
energy storage because of their outstanding properties like their large
surface area-to-volume ratio and flexible surface functionalities.
There are several approaches for NFs fabrication, for example,
drawing, template, phase separation, self-assembly, and
electrospinning, among which electrospinning is a simple, cost-
effective and versatile method for NFs production.
Regarding gas sensing applications, semiconductor metal oxide
(SMO) NFs sensors have a lot of promise due to their advantages of
SMO materials like low cost, simple fabrication, and high
compatibility with microelectronic processing. Furthermore, NFs
consist of many nanograins, therefore, grain boundaries are large,
surface-to-volume ratio is very high, and gases easily diffuse along
grain boundaries. As a result, an exceptionally high response was
observed in in SMO NFs gas sensors by electrospinning. Among
various SMO NFs prepared by electrospinning, α-Fe2O3 has become
a potential gas sensing material because of its low cost and thermal
stability and ability to detect many gases such as NO2, NH3, H2S, H2,
and CO. Besides, zinc ferrite ZnFe2O4 (ZFO), a Fe2O3-based ternary
spinel compounds, has been a promising material for detecting gases
thanks to its good chemical and thermal stability, low toxicity, high
specific surface area and excellent selectivity. Otherwise, H2S is a
colorless, corrosive, inflammable and extremely toxic gas which can
be rapidly absorbed by human lungs and easily causes diseases in
respiratory and nervous system, even deaths. However, until now,
very few studies on H2S gas sensing properties of α-Fe2O3 and ZFO
NFs, especially effects of parameters of fabrication process (i.e.
solution composition, heat treatment, and electrospun time) on
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morphology, structure and H2S gas sensing properties of the sensors
have been carried out although there have been some reports about
H2S gas sensitivity of the sensor of other nanostructures of α-Fe2O3
or ZFO sensors (e.g. nanochains, porous nanospheres, and porous
nanosheets (NSs)).
Furthermore, RGO, a GP reduced from GO produced from
graphite by Hummer method, has recently received world-wide
attention owing to its exceptional physicochemical properties. The
combination between SMO NFs and RGO to enhance gas sensing
performance through the formation of heterojunction was mentioned
in many works. However, up to present, there have been no reports
on incorporation of RGO in α-Fe2O3 and ZFO NFs for enhanced H2S
gas sensing performance.
Therefore, the thesis titled "Electrospinning of α-Fe2O3 and
ZnFe2O4 nanofibers loaded with reduced graphene oxide (RGO) for
H2S gas sensing application” was carried out to answer the concerns
mentioned above.
2. The study objective
The study objective of the thesis are listed as follows:
- To successfully fabricate on-chip sensors based on α-Fe2O3, ZFO
NFs and their loading with RGO by on-chip electrospinning.
- To explore the effect of parameters (i.e. solution composition,
heat treatment, electrospun time, and RGO concentration) of
fabrication process on the NF morphology, structure and H2S gas
sensing properties.
- To clarify H2S gas sensing mechanism of the sensors of α-Fe2O3,
ZFO NFs and their incorporation with RGO.
3. Research scope and content
The thesis uses α-Fe2O3, ZFO NFs and their loading with RGO, as
well as harmful gas H2S as object studies.
The study focuses on the following contents:
- To optimize some process parameters (i.e. solution composition,
heat treatment, electrospun time, and RGO concentration) for on-
chip sensor fabrication of α-Fe2O3, ZFO NFs and their loading
with RGO via electrospinning method.
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- To characterize the NFs and to analyze the relationship between
their morphology and microstructure of NFs with fabrication
process parameters.
- To examine H2S gas-sensing properties of the NFs sensors for
clarifying the relationship among morphology, microstructure
with gas-sensing properties of the NFs sensors.
- To understand the H2S gas-sensing mechanisms of α-Fe2O3, ZFO
NFs and their loading with RGO.
4. Research Methodology
To achieve the objectives, the thesis research was conducted by
experimental methods, namely:
- The on-chip electrospinning method was employed for the
fabrication of α-Fe2O3, ZFO NFs and their loading with RGO.
- Morphology and structure of the NFs were characterized by
TGA, RAMAN, FE-SEM, TEM, HR-TEM, SAED, EDX, and
XRD.
- The gas-sensing properties of the NFs were measured by a
home-made system using flow-through technique.
5. Practical and scientific significance of the thesis
The scientific relevance: The thesis results elaborated the
relationship among processing parameters, microstructure, and gas-
sensing properties of α-Fe2O3, ZFO NFs and their loading with RGO.
In addition, the thesis also clarified H2S gas-sensing mechanisms of
α-Fe2O3, ZFO NFs and their loading with RGO. Furthermore, the
research results have been reviewed by domestic and foreign
scientists, and published in prestigious journals such as Journal of
Hazardous Materials, Sensors and Actuator B, and Journal of Alloys
and Compounds which shows scientific significance of the
dissertation.
The practical relevance: This dissertation focused on the
development of the effective sub-pp H2S gas sensor of α-Fe2O3, ZFO
NFs and their loading with RGO by on-chip electrospinning method.
The optimized results provide a premise to develop the sensors for
environmental monitoring, occupational health, petrochemical plant,
which showed significantly practical relevance of the dissertation.