Luận văn improving the gas sensing property of wo3 nanomaterials

* SEM: Scanning electron microscope « FE-SEM: Field mission Scanming Electron Microscopy ¢ EDX or EDS: Energy-dispersive X-ray spectroscopy « TIM: ‘[ransmission electron microscopy ©

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MTNISTRY OF EDUCATION AND TRAINING HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGY

NGUYEN HOANG HUNG

IMPROVING THE GAS SENSING PROPERTY OF

WO; NANOMATERIALS

MAJOR: ENGINEERING PHYSICS

MASTER OF SCIENCE THESIS ENGINEERING PHYSICS

SUPERVISOR: Dr DANG DUC VUONG

HANOI - 2012

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ee BO GIAO DUC VA BAO TAO ina

TRUONG BAI TIOC BACH KIIOA HA NOL

NGUYEN HOANG HUNG

CUA VAT LIEU NANO WO;

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TABLE OF CONTENT

2.1, Characterized features of gas sensors based on metal oxides 4

2.2, Basic scientist approach ccsscssisuisveeseseeseeeetestasinnivanotaseivtnnseet 6

1 Tungsten oxide among metal oxides for gas detection 3

2, Structural propertios oŸ tungsien oxide à occcoseneeorererseooee TỔ

3 Gas sensors based on tungsten oxide eo ¬— 27

Nguyen Hoang Hung ; Master Thesis

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* SEM: Scanning electron microscope

« FE-SEM: Field mission Scanming Electron Microscopy

¢ EDX or EDS: Energy-dispersive X-ray spectroscopy

« TIM: ‘[ransmission electron microscopy

« LETS: Low energy ion scattering

* DA: Depletion approximation

Nguyen Hoang Hung it Master Thesis

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PREFACE

In this thesis, the WOs materials are synthesized and measured in NH gas sensor

application The morphological form of the material was deposited by wet chemical

methods combining hydrothermal technology Gas sessing properties of the materials

was improved by reducing in grain size and doping with FeyO, nanorods The thesis

title: “Improving the gus sensing properly of WO, material” was selected and the

Tesults are presented in three mam chapters:

Chapter I Introduction: A short introduction to chemical sensors based on

metal oxides, with a particular emphasis on WOs This chapter also includes the

inctivation, targcts and organization of this investigation

Chapter LL Experimental and methodology: Illustrating the experimental

details used in this work, method to amalyze the structural and morphological

properties of material, a gas effective sensing system was also built in this chapter

Chapter Tl Experimental and methodology: Anning af contributing lo the

understanding of the whole gas sensing process

inal Conclusions and future Outlook are also proposed in this thesis

Nguyen Hoang Hung vili Master Thesis

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1 WO¿ microsheets sựnthesis

3 Gas sensing properties

CIIAPTER 3: RISULT AND DISCUSSION

1 Tungsten trioxides microsheets

2 Tungsten trioxides nanyparticles and doping

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PREFACE

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PREFACE

Nowadays, the pollution level is increasing due to the misuse of chemicals in

industry, agriculuure as well as in life The presence of inflammable gases, toxic gases

that have caused large damage to both people and their property Aims to minimize

the risks as well as industrialization and modemization of industrial processes, it is

necessary to fabricate a kind of environmentally benign devices capable of detecting

gases Since then the term “gas sensor” was bom

TRunng the last decades of the century, the kind of gas se which was best

known, was based on the metal oxide semiconductor In particular, materials such as

Tia, SnOz, WOs, are widely used in gus sensing applications to detect toxic gases

‘The principle for gas sensing applications using metal oxide semiconductor based on

the change in resistance of the sensitive layer in presence of gases One of the metal

oxide material promising for semiconductor gas sensor applications was lungster

oxide With many advantages such as high sensitivity, low response time low

operating temperature, tungsten oxide material was gradually bronght to second pk

in the world of gas sensor based on metal oxides semiconductor (after SnO2)

One of the gases that was widely used and caused great impact on human health is

ammonia Recently, ammonia (NH;) is used in many industries, the NH gas leak in

the pipeline has caused serious consequences to health So, in the gases to be detected,

XH; in one of the most concerned gus and sensitive material to detect this gas thal was

emphasized by scientists is WO

Developing in parallel with nanotechnology, WO; is a sensitive materials even at

large sizes, but when the material reach to the size limit, the sensitivity was strongly

improved and appear more interesting properties Currently, there are many roules 1o

synthe

deposition (CVD), physical deposition However, these methods require a rigorous

technological processes and conditions It is difficult to obey in Vietnam science

condition Recently, wet chemical method combined with hydrothermal technology

emerged with many advantages as simple lechnology, inexpensive, nol undemanding

WO) manomaterials such as ball milling, thermal oxidation, chemical vapour

on teclmological process as well as technical conditions Moreover this method allows

mass production and variable morphologies could be synthesized ‘he above

advantages make wet chemical method has been studying and using more and more in

all over the world

Nguyen Hoang Hung vit Master Thesis

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PREFACE

synthe

all over the world

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LIST OF FIGURE

Figure 1 Chemical sensors

Figure 2 Cross-section of a chemical sensor

Figure 5 Schematic representation of banier foanadien

Figure 6 Three mechanisms of conductance

ure 7 Chemical (a) and electronic (b) sensitization schemes

Figure 8 Sol-gel processing options

Figure 9 Prossure/emperature map of inaterial processing techniques

igure 10, Particle processing by conventional and hydrothennal

Figure 11 General purpose pressure autoclave and white Teflon 1

Figure 12 VLS synthesis apparatus 18

Figure 13 Map of temperature variations in fimace 1

Figure 14 Schematic Mustration of nucleation and growth of ZnO nanorods 1

Figure 17 Spin coating be)

Figure 18 Dip coating - 1

Figure 19 Comparison of the papers published on gas sensors 2

Figure 20, Schematic model of crystalline W03 in the undistorted cubic phase 1

Figure 21 Structural model of the WO; grain surface - 26

Figure 22 NH3"s structure and symmetry axis

Figure 23 Sore types of armmotiia detector 1

Some of commercialized gas sursors head 1

Figure 25 Schematic diagram of WO; miorosheets synthesis 34

Figure 26 Steps of WO; nanoparticles svnthesis " 35

igure 27 Diagram of heat treatment 1

Figure 28 Electron scattermg and secondary signal generation,

Schematic diagram of an SEM

Pt interdigitated electrodes and heater used in system

Figure 31 Static gas sensing system and principal cireutt

Figure 32 Dynamic gas sensing system,

Nguyen Hoang Hung Master Thesis

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LIST OF TABLE

‘Table 1 Sign of resistance change to change in gas atmosphere [93] 4

Table 2 Typical deposition techniques 20

Table 3 Known polymorphs of tungsten trioxide senessneennesneiensnneneeneee 26

‘Table 4, Occupational Lixposure Standards 2000,

'Table 5 3ome properties of NH; kinh tien

Table 6 Requirements for NIh gas detection equipment - 29

Table 7 Selected publications on Ny gas sensors based on WO; 31

Nguyen Hoang Hung l Master Thesis

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LIST OF TABLE

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PREFACE

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LIST OF FIGURE

Figure 34 The XRD pattem and EDX pattem of W0s thin film 4

Figure 36 FESEM images of WO; nanoparticles

Figure 37 SEM images of WO; nanomaterials

Figure 38 EDX partner of #203 nanorods doped WO, 1% wt

Figure 41 Response to NH3 of WOs microsheets at L60°C wae ssssssesssteseneeeee 4

Figure 43 The sensor response as a function of gas concentration 49

Figure 44 Response to NH3 of WOs nanoparticles at 55 °C

Figure 45 Rosponse to NHy of WO, nanoparticles al 95 °C

Figure 47 Response to NII; of WO nanoparticles at 294 °C 1

Figure 48 The dependence of the sensor response on operating temperature 1

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LIST OF FIGURE

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PREFACE

synthe

all over the world

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LIST OF FIGURE

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PREFACE

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LIST OF FIGURE

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LIST OF TABLE

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LIST OF FIGURE

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LIST OF FIGURE

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LIST OF FIGURE

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PREFACE

synthe

all over the world

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LIST OF FIGURE

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LIST OF TABLE

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LIST OF FIGURE

Tiêu đề	Improving the gas sensing property of wo3 nanomaterials
Tác giả	Nguyen Hoang Hung
Người hướng dẫn	Dr. Dang Duc Vuong
Trường học	Hanoi University of Science and Technology
Chuyên ngành	Engineering Physics
Thể loại	Luận văn
Năm xuất bản	2012
Thành phố	Hanoi

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