Fe2O3 Humidity Project

8/8/2019 Fe2O3 Humidity Project

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Studies on humidity sensing behavior of «««

M.Sc. Project -2009-10

1

Abstract

Hematite (E-Fe2O3) nanorods were successfully synthesized without any

templates by calcining the goethite (E-FeOOH) precursor in air at 300oC for 2 h.

The E-FeOOH precursor was prepared through a simple and low cost wet chemical

route by using iron sulphate (FeSO4,7H2O) and sodium acetate (CH3COONa) at 40

oC. The E-FeOOH precursor and E-Fe2O3 nanorods were characterized by using X-

ray diffraction (XRD) measurements, thermogravimetric analysis (TGA), Fourier

transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS)

and field emission scanning electron microscopy (FE-SEM). To demonstrate the

practical applications of the synthesized E-Fe2O3 nanorods, we investigated their

humidity sensing properties. The E-Fe2O3 nanorods exhibits humidity sensing

properties such as higher humidity response (~663% at 95% RH), response time

(~ 199 s), recovery time (~190 s), hysteresis within 1% and excellent repeatability.

Due to the fact that it has an excellent humidity sensing characteristics and can be

synthesized easily, the E-Fe2O3 nanorods would be an ideal candidate for application

in humidity sensors.





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1. Introduction

Humidity sensors are useful for the detection of the relative humidity (RH) in various

environments. The measurement and control of humidity are important in a wide variety of

commercial and industrial applications, including those associated with building ventilation

control, clean rooms in the semiconductor and automotive industries, environmental

chambers for the testing of electronics, industrial drying, and process monitoring in the

chemicals, electronics, food/beverage, pharmaceutical, cosmetics and biomedical analysis

industries.

The term moisture generally refers to the water content of any material, but for

practical reasons, it is applied only to liquids and solids, whereas the term humidity is

reserved for the water vapor content in gases. There are many ways to express moisture and

humidity, often depending on the industry or the particular application. The moisture of

gases is expressed sometimes in pounds of water vapor per million cubic feet of gas. The

moisture in liquids and solids is generally given as a percentage of water per total mass (wet-

weight basis), but may be given on a dry-weight basis. The moisture in liquids with low

water miscibility is usually expressed as parts per million by weight (PPMw).

Two common parameters associated with humidity measurement are absolute

humidity and relative humidity. The absolute humidity is the density of the water vapor

component. It can be measured, for example, by passing a measured quantity of air through

a moisture-absorbing substance (such as silica gel) which is weighted before and after the





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absorption. Absolute humidity is expressed in grams per cubic meter or in grains per cubic

foot. The absolute humidity is not generally useful in engineering practice because it is a

function of atmospheric pressure.

The RH is defined as the ratio of the water -vapor pressure present to the water -vapor

pressure required for saturation at a given temperature. The relative humidity is related to

ambient temperature. Water vapor is a natural component of air, and the RH of the water

vapor and air mixture is defined as the ratio of the mass of water vapor in a unit volume

compared to the mass of water vapor which that volume could hold if the vapour were

saturated at the mixture temperature. The RH is typically expressed as :

where P w and P s are the vapor and saturation pressures, respectively.

Humidity can be measured by instruments called hygrometers. The first hygrometer

was invented by Sir John Leslie (1766±1832). The detection of humidity is mainly based on

the response of electric devices or a change of spectral response. Electric devices are usually

composed of capacitors, resistors, or semiconductors that are sensitive to moisture, in which

their electrical resistance and/or capacitance vary depending on the degree of adsorption of

moisture. The change in color of a sensing material exposed to a humid atmosphere results

in the spectral variation. Various types of humidity sensors have been marketed, however,

they are far from satisfactory since a linear response to humidity is valid only in a limited

range and hysteresis is often involved in the measurement of the response and humidity

curves. Thus, it is very much necessary to develop a humidity sensor with complete set of





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characteristics like, good linearity, high sensitivity, low hysteresis, rapid response time and

obviously with low cost.

The materials that have been studied for the development of humidity sensors

include polymers, ceramics and composites, which have their own merits and specific

conditions of application. The importance of humidity sensing has been well understood in

most recent times and considerable attention has been focused on the development of

humidity sensitive materials.

Currently, one-dimensional (1-D) nanostructures, such as nanorods, nanowires,

nanobelts, and nanotubes, have become the focus of intensive research not only for their

peculiar properties but also for many potential applications in catalysis, electronics,

photonics, drug delivery, medical diagnostics, sensors, and magnetic materials. Hematite (E-

Fe2O3) is the most stable iron oxide with n-type semiconducting properties ( E g = 2.2 eV)

under ambient conditions. It has been intensively investigated because of its wide

applications in catalysts, pigments, magnetic materials, gas sensors, and lithium ion

batteries. For its excellent properties, much attention has been directed to the controlled

synthesis of one-dimensional (1-D) E-Fe2O3, such as nanofibers, nanorods, nanowires,

nanobelts and nanotubes by a variety of techniques and methods. Wang et al. prepared

E-Fe2O3 nanobelts and nanowires via a gas-solid reaction process under 700 and 800 °C.

Mann et al. synthesized E-Fe2O3 nanotubes by using biomacromolecules as templates.

Yi-Xie et al. prepared E-Fe2O3 nanorods through a hydrothermal process at 120 °C. The

preparation of E-Fe2O3nanotubes with alumina membranes as the substrates was also

employed by many researchers. However, the gas-solid reaction usually requires special





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equipment and high temperatures, the methods employing templates or substrates often

suffer from disadvantages related to the high cost and the removal of impurities and the

hydrothermal process usually needs tedious reaction times. It is still a challenge to develop

simple, low-cost, and environmentally friendly approaches for the synthesis of 1-D

structural E-Fe2O3.

The objectives of the present study are ±(a) to synthesize E-Fe2O3 nanorods by using

a simple wet chemical route, (b) to characterize the resulting E-Fe2O3 nanorods by using the

XRD, FTIR, TGA, XPS and FE-SEM and (c) to explore the possibility of using the

synthesized E-Fe2O3 nanorods as sensing material for humidity. In the present project work,

the E-Fe2O3 nanorods were synthesized without any templates via a low-temperature (40 °C)

solution approach. In this work, the precursor of E-FeOOH nanorods was first prepared by

using FeSO4 ·7H2O as the iron source material in the presence of CH3COONa in an aqueous

solution. The CH3COONa was used as a source of hydroxide ions during the hydrolysis of

iron salts to form iron oxyhydroxide (FeOOH). Then E-Fe2O3 nanorods were obtained by

the calcination of as- prepared E-FeOOH at 300 °C for 2 h. Humidity sensing characteristics

such as relative humidity (RH)-resistance property, humidity hysteresis, response time and

repeatability of the E-Fe2O3 nanorods were investigated.





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2. Experimental

2.1. Materials

All chemicals were of analytical grade. The iron sulphate (FeSO4, 7H2O) and

sodium acetate (CH3COONa) were purchased from E-Merck (India) and were used without

further purification.

2.2. Synthesis of the E-Fe2O3 nanorods

In this work, the E-Fe2O3 nanorods were synthesized without any templates by

calcining the E-FeOOH precursor in air at 300oC for 2 h. Fig. 2.1 is a schematic

representation of the synthesis procedure. The E-FeOOH precursor was prepared through a

simple and low cost wet chemical route. The FeSO4,7H2O was used as the source of Fe2+

and the CH3COONa was used as the precipitating agent to release hydroxyl ions slowly

during the reaction. In a typical experiment, the aqueous solution containing 0.1M

F

eSO4,

7H2O and 0.1 M CH3COONa was prepared in double distilled water and stirred

continuously using a magnetic stirrer for 2 h at 40oC to obtain a yellow colored precipitate.

The resulting precipitate was filtered and washed with double distilled water and alcohol

several times to remove impurities and by products present in the product. The precipitate,

thus formed was dried at 40oC under vacuum for 2 h and grinded into a powder, which is

the E-FeOOH precursor. The E-FeOOH precursor was calcined in air at 300oC for 2 h to

obtain the E-Fe2O3 nanorods. The color of the E-FeOOH precursor was changed from

yellow to red during calcination.





7

Fig. 2.1 : A schematic diagram of the synthesis procedure for E-Fe2O3

E-FeOOH precursor

Aqueous solution of FeSO4, 7H2O (0.1 M)

Add 0.1 M aqueous

solution of CH3COONa

Keep solution withcontinuous stirring at

40 oC for 2 hours

Filter and wash the

resulting yellow coloredprecipitate and dry it at

40° C in air

Grind the resulting

powder

Calcinate at 300 ° Cfor 2 h

E-Fe2O3 nanorods





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2.3. Characterization

X-ray diffraction (XRD) analysis was performed with a Bruker diffractometer (D8,

Advance, Bruker AXS model) with CuK E radiation (=1.5406 nm) operating at 40 kV and

40 mA. The field emission scanning electron (FE-SEM) microscopy analysis was carried out

with a Hitachi (S-4800, Hitachi, Japan) microscope. The FTIR spectroscopy analysis was

performed with a Nicolet FTIR spectrometer (IMPACT 420 DSP) by the conventional KBr

method in the spectral range 4000-400 cm-1

. Thermogravimetry-differential thermal analysis

(TG-DTA) of the E-FeOOH precursor was carried out with a TA instrument ( TGA 2950)

in air atmosphere at the rate of 10oC/min from room temperature to 800

oC.

2.4. Humidity sensing study

The E-Fe2O3 nanorods powder was pressed into pellets (diameter ~1 cm and thickness

~0.1 cm) under a pressure of 15 MPa for the humidity sensing study. The electrical contact

leads were fixed 0.7 cm apart with the help of silver paste on the surface of the pellet. The

electrical resistance of the pellet was measured as a function of relative humidity (RH) by using

a simple two probe configuration with a sensitive digital multimeter (2000 Digital multimeter,

Keithley) controlled by a personal computer.

The continuous variation in humidity was achieved in a simple experimental set-up

fabricated in our laboratory in order to investigate the humidity sensing properties. The two

temperature method is used to measure the relative humidity. The experimental set-up mainly

consisted of a closed flask (1000 ml) with two necks for inserting thermometers and the

sensing element (i.e. the pellet of the composite). The flask was partially filled with water and

kept in a glass container. The sensing element along with the thermometer was mounted on the







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3. Results and Discussion

3.1. XRD results

Fig.3.1shows The XRD pattern of the as- prepared precursor is shown in Fig.1(a). It

exhibits the diffraction peaks at 2 U values of 19.08o, 31.36o, 36.97o, 45.02o, 59.42o and

65.37o, which are attributed to the formation of orthorhombic E-FeOOH phase (JCPDS #

29-0713). This E-FeOOH precursor was calcinied at 300oC in air for 2 h. The XRD pattern

of the calcinied E-F

eOOH precursor is show

n inF

ig.3.2. It indicates the diffractions peaks at

2 U values of 23.98o, 33.14

o, 35.57

o, 40.85

o, 49.58

o, 53.99

oand 63.93

ocorresponding to the

rhombohedral corundum phase of iron(III) oxide (hematite) (JCPDS # 33-0664). No other

peak corresponding to hydroxide or impurities were observed. This confirmed that the E-

FeOOH precursor has transformed completely into hematite on calcination at 300oC for 2 h.

The crystallite size was calculated by using the Scherrer formula ±

where t is the average size of the crystallite, assuming that the grains are spherical, k is 0.9,

is the wavelength of X-ray radiation, B is the peak full width at half maximum (FWHM) and

U is the angle of diffraction. The crystalline size of E-Fe2O3 is found to be ~ 5-10 nm.

3.2. FTIR spectroscopy results

The FTIR spectrum of the as- prepared precursor is shown in Fig.3.3. This spectrum

exhibits the bands around 3131 and 1639 cm-1

, corresponding to the stretching modes of





11

20 30 40 50 60 70 80

2200

2400

2600

2800

[ 1

7 0

]

[ 1

1

2 ]

[ 0

6

1 ]

[ 0

0

2 ]

[ 1

5

1 ]

[ 2

3

1 ]

[ 2

2

1 ]

[ 0

4

1 ]

[ 1

3

1 ] [

1

4

0 ]

[ 1

2

1 ]

[ 1

1

1 ]

[ 0

2

1 ]

[ 1

3

0 ]

[ 1

1

0 ]

[ 0

2

0 ]

I n t n s i t y (

r b i t

r r y U n i t s )

2 U ( gr )

Fig.3.1 : XRD pattern of the E-FeOOH precursor.





12

20 30 40 50 60 70 80

2200

2400

2600

2800

3000

[ 3 0 0 ]

[ 1 1 6 ]

[ 0 2

4 ]

[ 1 1

3 ]

[ 1 1 0 ]

[ 1 0 4 ]

[ 0 1 2 ]

I n t e n s i t ( A

r i t r a r

n i t s )

2 U (de ree)

Fig.3.2 : XRD pattern of the powder calcinied at 300oC for 2 h in air.





13

Fig.3.3 : FTIR spectrum of the E-FeOOH precursor.

4000 3600 3200 2800 2400 2000 1600 1200 800 400

20

40

60

80

100

120

632

800891

1135

1639

3131

T r a n s m i t t a n c e ( % )

Wavenum er (cm-1)





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OH. Two bands at ~891 and 800 cm-1 can be assigned to Fe-O-H bending vibrations in

the E-FeOOH and these bands are usually used for identification of E-FeOOH in a

qualitative phase analysis of iron oxide mixtures. The band at ~632 cm-1

corresponds to the

Fe-O stretching vibrations in E-FeOOH. The FTIR spectrum of the E-FeOOH precursor

calcinied at 300 oC for 2 h [Fig.3.4] exhibits the bands at ~539 and 452 cm-1 which

corresponds to the characteristic bands of ferric oxides.

3.3. TGA analysis

The TG curve of the as- prepared E-FeOOH precursor is shown in Fig. 3.5. It

exhibits two major weight losses in the temperature range 30-188 oC and 188-265 oC. In the

first step, the weight loss initiates practically from room temperature to 188oC, with a

weight loss of ~4% due to the desorption of physically adsorbed water. The second weight

loss step observed from 188oC and is continued up to 265

oC, with a weight loss of ~12%. It

is associated with the dehydroxylation of E-FeOOH precursor to form E-Fe2O3. This result

is in agreementw

ith the XRD andF

TIR data of the calcinied precursor w

hich show

s the

transformation of as- prepared E-FeOOH precursor to E-Fe2O3, on calcination at 300oC for 2

h.

3.4. XPS results

To further ascertain the formation of E-Fe2O3, the XPS analysis of the calcinied

E-FeOOH precursor was performed. The XPS survey spectrum of the calcinied E-FeOOH

precursor [Fig.3.6] shows the presence of Fe 2p (56%) and O 1s (31%). The deconvoluted

Fe 2p spectrum [Fig.3.7] is comprised of two peaks at 711.40 and 724.80 eV, which

corresponds to the Fe 2p3/2 and Fe 2p1/2, respectively. This is consistent with the previously





15

Fig.3.4 : FTIR spectrum of the E-Fe2O3 nanorods.

4000 3600 3200 2800 2400 2000 1600 1200 800 400

0

20

40

60

80

100

452539

943

105511291632

3397

T r a n s m i t t a n c e ( %

)

Wavenum er (cm-1)





16

Fig.3.5 : TGA curve of the E-FeOOH precursor.

0 200 400 600 800

82

84

86

88

90

92

94

96

98

100

M a s s l

s s ( %

)

r at r (

)





17

Fig.3.6 : XPS survey spectrum of E-Fe2O3 nanorods.

0 200 400 600 800 1000 1200

400

600

800

1000

1200

Fe 2p1/2

Fe 2p3/2

O 1s

I n t e n s i t y (

r b .

U n i t s )

Binding Energy (eV)





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Fig.3.7: Deconvoluted Fe 2p spectrum

700 710 720 730

0

400

800

1200

1600

724.8 eV

718.5 eV

711.4 eV(b)

I n

t e n s i t y (

r b i t r a r y

n i t s )

Binding energy (eV)





19

reported values 710.8 and 724.8 eV for the bulk E-Fe2O3. The energy difference between

Fe 2p3/2 and Fe 2p1/2 peaks is 13.4 eV. This value is characteristic of Fe3+ state indicating the

formation of the E-Fe2O3 by the experimental methodology used. Furthermore, Fe3+

satellite

peak is observable in the spectrum at 718.5 eV, above the Fe 2p3/2 peak. The deconvoluted O

1s spectrum [Fig.3.8] is deconvoluted into two peaks at 530.41 and 532.11 eV, which are in

good agreement with the literature values of E-Fe2O3. The dominant peak located at 530.41

eV corresponds to the oxygen bonded as E-Fe2O

3. The second peak at 532.11 eV is

probably due to a hydroxide. Thus, the Fe 2p and O 1s spectra indicate that the valence states

of elements Fe and O are +3 and -2, respectively. The XPS results in conjunction with XRD

and FTIR data confirm the formation of pure E-Fe2O3 when the E-FeOOH precursor was

calcinied at 300 oC in air for 2 h.

3.5. Morphological analysis

The surface morphologies of the as- prepared E-FeOOH and E-Fe2O3 nanorods were

characterized by FESEM. The FESEM image of the as- prepared E-FeOOH precursor

[Fig.3.9] shows uniform rods or somatoid structures, which is characteristic crystallizing

shape of the E-FeOOH. The FESEM image of the E-Fe2O3 nanorods [Fig.3.10] is similar to

that of the E-FeOOH precursor. This marks the topotactic transformation of E-FeOOH

precursor to E-Fe2O3 nanorods preserving the shape of the starting material during the

thermal conversion. The nanorods have an aspect ratio (ratio between the diameter ~ 40 nm

and length 300 nm of the sample) of ~ 7 as evidenced from the FESEM.





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Fig.3.8: Deconvoluted O 1s spectrum

522 524 526 528 530 532 534 536 538 540

0

200

400

600

800

1000

1200

532.11 eV

530.41 eV

I n t e n s i t ( A

r i t r a r u n

i t s )

indin ener (eV)





21

Fig.3.9 : F E S E M image of the E-FeOOH precursor.





22

Fig.3.10 : F E S E M image of the E-Fe2O3 nanorods.





23

3.6. Formation process

The schematic diagram of the process is described in Fig.3.11. In the first stage, the

E-FeOOH crystal nucleus formed by the reaction of Fe2+

with O2 and OH-

produced by the

hydrolysis of CH3COO-. Then these E-FeOOH particles further assembled into rodlike

structures by combining together with OH groups. Finally, the E-Fe2O3 nanorods formed

with the removal of H2O after being calcined at 300 °C in air. The equations of the reactions

in the synthetic process are as follows :

3.7. Humidity sensing performance

3.7.1. Resistance - RH characteristics

The variation in resistance of E-F

e2O3 nanorods as a function of RH are show

n in

Fig. 3.12. The resistance is about 1.99 x 107

in 18% RH air, while it decreased to about

2.59 x 106 ; in 100% RH air. Therefore, the resistance changed approximately one order of

magnitude over the RH range of 18-100% RH, showing good sensitivity to humidity. The

dashed line shows the exponential fit (y = 2.46 x 106 + 3.52 x 107 x e(-x/25.63), R 2 = 0.9987,

where x, y and R 2

represent the %RH, resistance and correlation coefficient, respectively.) to

the experimental data, illustrating clearly good quality of the fit. Thus, whole range of

humidity i.e. 18-100% RH used in the present experiment was observed to be the

operational range for the E-Fe2O3 nanorods.





24

FeSO4 + O2 +

CH3COONa Nucleation Combining

Calcination

-FeOOH nanoparticles -FeOOH nanorods

-Fe2O3 nanorods

Fig.3.11 : Schematic diagram of the formation process of E-Fe2O3 nanorods.





25

0 20 40 60 80 100 120

0.0

3.0x106

6.0x106

9.0x106

1.2x107

1.5x107

1.8x107

2.1x107

R e s i s t a n c e

( ; )

%RH

Fig.3.12 : V ariation of resistance with R H for E-Fe2O3 nanorods. T he dashed line

represent the exponential fit to the experimental data.





26

In order to reveal the characteristics of the E-Fe2O3 nanorods towards moisture, the

humidity response for detecting the humidity was calculated using the expression-

where R d and R h are the values of the resistance recorded at 18 % RH and at a particular RH,

respectively. The variation of the humidity response with RH for the E-Fe2O3 nanorods is

shown in Fig.3.13. It was observed that the humidity response increases with an increase in

the RH. It is found that the humidity response can be empirically represented as y = 73.57

+0.76 * x + 0.06 * x2, R

2= 0.9969, where x, y and R

2represents % RH, humidity response

and correlation coefficient, respectively. The dashed line shows the polynomial fit to the

experimental data, illustrating clearly good quality of the fit. Thus, the E-Fe2O3 nanorods

can be reliably used to monitor the RH in the range 18-100 % RH.

3.7.2. Hysteresis

Hysteresis is an important parameter for evaluating the performance of a humidity

sensor. The hysteresis curves for E-Fe2O3 nanorods was obtained by measuring the

resistances as a function of RH for the high (100% RH) -low (18% RH)- high (100% RH)

cycle and the corresponding hysteresis curves are presented in Fig.3.14. It is seen that the

differences in resistance values of the E-Fe2O3 nanorods for low (18% RH) ± high (100%

RH) (i.e. humidification process, black circles) and high (100% RH) - low (18% RH) (i.e.

desiccation process, red circles) are within 1%, which indicates a good reliability of E-Fe2O3

nanorods.





27

20 40 60 80 100

0

100

200

300

400

500

600

700

800

H u m i d i t y r e s p o n s e

( % )

% RH

Fig.3.13 : V ariation of humidity response with R H for E-Fe2O3 nanorods. T he

dashed line represent the polynomial fit to the experimental data.





28

0 20 40 60 80 100 120

0.0

3.0x106

6.0x106

9.0x106

1.2x107

1.5x107

1.8x107

2.1x107

R e s i s t a n c e ( ; )

%RH

Fig.3.14 : Humidity hysteresis for E-Fe2O3 nanorods.





29

3.7.3. Response and recovery times

In order to utilize the E-Fe2O3 nanorods as a humidity sensor, it is important to

know the rate of response to the variation of RH. The resistance of E-Fe2O3 nanorods was

monitored at two extreme humid atmospheres (27% and 94% RH). The sensor was

transferred from a chamber (27% RH) to another chamber (94% RH) and then transferred

back. The resulting response and recovery characteristics are shown in Fig.3.15. Although,

the sensing element was exposed to the surrounding air (i.e. laboratory environment) during

the transfer process, the transfer time (~ 1-2 s) is much smaller than the response and

recovery times of the sensor and therefore, the correctness of this experiment is acceptable.

According to literature, the time taken by a sensor to achieve 90% of the total resistance

change is defined as response time in the case of adsorption or the recovery time in the case

of desorption. The E-Fe2O3 nanorods exhibit the response and recovery times of ~ 199 and

190 s at the humidification and desiccation steps, respectively.

3.7.4. Reproducibility and reversibility

The reproducibility and reversibility are important parameters to consider when

evaluating the performance of a sensor. The resistance of E-Fe2O3 nanorods was measured

by exposing them repeatedly to 27% RH and then to 94% RH atmospheres to examine the

reproducibility and reversibility. The measurements were repeated for three cycles and the

resulting response and recovery characteristics are shown in Fig.3.16. It was seen that the

resistance value of the E-Fe2O3 nanorods reverts always to the original one when RH is

restored to the former state, which indicates that the humidity sensing process is extremely

reversible. The response and recovery times does not change during the four cycles of





30

0 100 200 300 400 5001.0x10

6

4.0x106

8.0x106

1.2x107

1.6x107

2.0x107

94% RH humidification

27% RH desiccation


Time (s)

Fig.3.15 : Response and recovery characteristics of E-Fe2O3 nanorods.





31

0 500 1000 1500 20001.0x10

6

4.0x106

8.0x106

1.2x107

1.6x107

2.0x107

94% RH humidification

27% RH desiccation


Time (s)

Fig.3.16 : Repetitive response of E-Fe2O3 nanorods when exposed to

four high (94% R H)-low (27% R H)-high (94% R H) cycles.





32

measurements, indicating a good reproducibility of the response of the E-Fe2O3 nanorods.

Thus, the E-Fe2O3 nanorods exhibited good stability as well as an excellent reproducibility

of the response. This suggests that the E-Fe2O3 nanorods can be used as a reusable sensing

material for humidity.





33

4. Conclusions

In this project work, we have presented a simple and low cost route for synthesizing

E-Fe2O3 nanorods via a template free solution approach at low temperature (40oC). The

following main findings resulted from the present investigation ±

y We have successfully synthesized the E-Fe2O3 nanorods at low cost by using a

solution approach at 40oC using FeSO4 ·7H2O as the iron source material in the

presence of CH3COONa in an aqueous solution. The resulting nanorods were

characterized by XRD, FTIR, TGA, XPS and FE-SEM.

y The formation of E-FeOOH precursor and its topotactic transformation to E-Fe2O3

upon calcinations was confirmed by XRD, FTIR, TGA, XPS and SEM analysis.

y This study thus offers a simple, low cost, short process, template free and

environmentally friendly solution approach to synthesize E-Fe2O3 nanorods.

y The E-Fe2O3 nanorods exhibits humidity sensing properties such as higher humidity

response (~663% at 95% RH), response time (~ 199 s), recovery time (~190 s),

hysteresiswithin 1% and excellent repeatability.

y Due to the fact that it has an excellent humidity sensing characteristics and can be

synthesized easily, the E-Fe2O3 nanorods would be an ideal candidate for application

in humidity sensors.





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Fe2O3 Humidity Project