chapter v preparation and characterization of...

133

CHAPTER V

PREPARATION AND CHARACTERIZATION OF INDIUM AND VANADIUM

DOPED TIN OXIDE: MWCNT COMPOSITE

Objectives:

i. To modify the surface of the MWCNT by coating Indium and Vanadium doped

Tin Oxide for improving the gas – sensing parameters.

ii. To study the impact of microwave irradiation and sonication on the composite.

iii. To study the structural, morphological and optical properties of the composite.

iv. To test the room temperature gas sensing ability of Indium and Vanadium

doped Tin Oxide: MWCNT composite on exposure to a reducing gas of low

concentration.

Fig. 5 Flowchart of preparation and characterization of Indium and

Vanadium doped Tin Oxide: MWCNT composite

134

0 20 40 60 80 100

0

50

100

150

200

250

300

350

400

450

In(6

55

)

In(8

20

)

Sn

(11

2)

V(2

21

)

V(3

07

)

C(1

00

)

Sn

(32

1)

Sn

(20

0)

Sn

(10

1)

Sn

(21

1)/

C(1

02

)

Sn

(11

0)/

C(0

02

)

Inte

nsi

ty (

arb

. u

nit)

2 degree

2f

5.1 Preparation of Indium and Vanadium doped Tin Oxide: MWCNT composite

The surface of the MWCNT was modified using Indium and Vanadium doped Tin

Oxide by chemical-solution route [1]. Multiwalled Carbon nanotubes were purchased from

Aldrich (0.D 10-15 nm, 1.D-2-6 nm, length 0.1-10 μm, purity >90%) chemicals and washed

with distilled water and ethanol for further purification. Tin (II) Chloride (SnCl2.2H2O),

Indium (III) Chloride (InCl3) and Vanadium (II) Chloride (VCl2) were taken as starting

precursor for the source of Tin, Indium, and Vanadium. Tin (II) Chloride of 0.5 mg was

dissolved in 10 ml of isopropyl alcohol and the same concentration of Indium (III) Chloride

and Vanadium (II) Chloride (VCl2) were taken. Then 80% of Tin (II) Chloride solution along

with 20% of Indium Chloride and Vanadium (II) Chloride solution were mixed together

and stirred using magnetic stirrer for 2 hours. Viscous sol was attained after 24 hours of

aging. MWCNT of 0.13 g were mixed well with the 1.5 ml of prepared precursor solution.

Then the mixer was divided into three samples, one out of them was treated with microwave

for 15 minutes, other sonicated for 5 minutes and then another was used as as-prepared

sample. Then the three samples were annealed to 500◦C in the furnace for one hour. After the

heat treatment the as-prepared, microwave assisted and sonicated samples were put under

various characterization techniques. Fig. 5 represents the flowchart of preparation and

characterization of Indium and Vanadium doped Tin Oxide: MWCNT composite

5.2 Structural studies of Indium and Vanadium doped Tin Oxide: MWCNT composite

Fig. 5.1 X-ray diffraction of as-prepared Indium and


135

Fig. 5.1 represents the X-ray diffraction pattern of as-prepared Indium and Vanadium

doped Tin Oxide: MWCNT composite. The X-ray diffraction pattern was obtained by using

copper Kα radiation of wavelength 1.54 Ǻ. The lattice parameters for the peaks

corresponding to Tin Oxide revealed the cell parameters a=4.8Ǻ and c=3.2 Ǻ. The

diffraction pattern constitutes the characteristic peaks of Tin Oxide, Indium, and Carbon

nanotube. The strong peaks at 26.38, 33.67, and 51.48 corresponds to the (110), (101), and

(211) planes of Tin Oxide. The minor peaks at 37.76 and 78.80 correspond to the (200) and

(222) planes of Tin Oxide respectively. The XRD data obtained is in good agreement with

the JCPDS no 88-0287 corresponding to the tetragonal structure of Tin Oxide. The peaks at

77.60 and 89.82 correspond to (820) and (655) planes of cubic structure of Indium Oxide

which is in good agreement with a JCPDS no 89-4595. The peaks at 30.47 and 57.92

correspond to (301) and (221) planes of orthorhombic structure of Vanadium Oxide which is

in good agreement with a JCPDS no 89-0612. The peaks at 26, 42.51, 44, 50.28, correspond

to (002) [2], (100), (101), (102) planes of Carbon nanotubes and is in good agreement with

the JCPDS no.75-1621 [3, 4]. The peaks at 26 and 50 of Carbon nanotubes are overlapped

with the strong peaks of Tin Oxide.

Table 5.1 Structural parameters of as-prepared Indium and Vanadium doped Tin Oxide:

MWCNT composite

Treatment h k l 2θ(deg) d(A◦) FWHM D

(nm)

a(Ǻ)

As-prepared

1 1 0

1 0 1

2 1 1

26.3504

33.6909

51.6098

3.37855

2.65812

1.76955

2.21030

1.81820

2.30540

03

04

03

a=4.8

c=3.2

136

Table 5.2 Dislocation density and strain of as-prepared Indium and Vanadium doped Tin Oxide:

MWCNT composite

Fig. 5.2 X-ray diffraction of microwave assisted Indium

doped Tin Oxide: MWCNT composite

Fig. 5.2 represents the X-ray diffraction pattern of microwave assisted Indium Vanadium

doped Tin Oxide: MWCNT composite. The lattice parameters for the peaks corresponding to

Tin Oxide revealed the cell parameters a=4.7 Ǻ and c=3.1 Ǻ. The diffraction pattern

constitutes the characteristic peaks of Tin Oxide, Indium, and Carbon nanotube. The strong

peaks at 26.21, 33.67, and 51.48 corresponds to the (110), (101), and (211) planes of Tin

Oxide. The minor peaks at 37.76 and 54.73 correspond to the (200) and (220) planes of Tin

Oxide respectively. The XRD data obtained is in good agreement with the JCPDS no 88-

0 20 40 60 80 100

0

100

200

300

400

500

600

700

In(6

55

)

In(6

22

)

V(4

11

)

Sn(3

21

)

V(2

13

)

In(5

43

)S

n(3

10

)S

n(0

02

)S

n(2

20

)S

n(2

11

)/C

(10

2)

Sn(2

00

)

V(3

21

)S

n(1

01

)

Sn(1

10

)/C

(00

2)

Inte

nsity

(arb

. u

nit)

2 degree

2fm

Treatment Dislocation

density (δ)

(x1016

)

Strain (ε)

(x10-3

)

As-prepared

11

6

11

7.3

4.75

6.75

137

0287 corresponding to the tetragonal structure of Tin Oxide. The peaks at 64.90 and 89.69

correspond to (543) and (655) planes of cubic structure of Indium Oxide which is in good

Table 5.3 Structural parameters of microwave assisted Indium and Vanadium doped Tin

Oxide: MWCNT composite

agreement with a JCPDS no 89-4595. The peaks at 30.475, 45.40, and 61.66 correspond to

(301), (321), and (411) planes of orthorhombic structure of Vanadium Oxide which is in good

agreement with a JCPDS no 89-0612. The peaks at 26, 42, 50, correspond to (002), (100),

(102) planes of Carbon nanotubes. The peaks at 26 and 50 of Carbon nanotubes are

overlapped with the strong peaks of Tin Oxide.

Table 5.4 Dislocation density and strain of microwave assisted Indium and Vanadium doped

Tin Oxide: MWCNT composite

Treatment h k l 2θ(degree) d(Å) FWHM D

(nm)

a(Ǻ)

Microwave

assisted

1 1 0

1 0 1

2 1 1

26.3837

33.7310

51.6613

3.37536

2.65505

1.76791

0.7539

0.6985

0.8227

10

11

10

a=4.7

c=3.1


density (δ)

(x1015

)

Strain (ε)

(x10-3

)

Microwave

assisted

10

8.26

10

2.43

2.39

2.25

138

Fig. 5.3 X-ray diffraction of sonicated Indium and Vanadium

doped Tin Oxide: MWCNT composite

Fig. 5.3 represents the X-ray diffraction pattern of sonicated Indium Vanadium doped

Tin Oxide: MWCNT sample. The lattice parameters for the peaks corresponding to Tin

Oxide revealed the cell parameters a=4.7 Ǻ and c=3.1 Ǻ. The diffraction pattern constitutes

the characteristic peaks of Tin Oxide, Indium, and Carbon nanotube. The strong peaks at

26.5, 33.8, and 51.7, and corresponds to the (110), (101), and (211) planes of Tin Oxide. The

minor peaks at 37.9 and 78.7 correspond to the (200) and (321) planes of Tin Oxide

respectively. The XRD data obtained is in good agreement with the JCPDS no 88-0287

corresponding to the tetragonal structure of Tin Oxide.

The peaks at 77.7 and 89.8 correspond to (820) and (655) planes of cubic structure of

Indium Oxide which is in good agreement with a JCPDS no 89-4595. The peaks at 30.9,

45.3, 57.9, and 71.545 correspond to (301), (411), (221), and (213) planes of orthorhombic

structure of Vanadium Oxide which is in good agreement with a JCPDS no 89-0612. The

peaks at 26, 42, 50, correspond to (002), (100), (102) planes of Carbon nanotubes.

The peaks at 26 and 50 of Carbon nanotubes are overlapped with the strong peaks of

Tin Oxide.All the composite‟s diffraction peaks are assigned well to tetragonal rutile

0 20 40 60 80 100

0

100

200

300

400

500

C(1

00

) Sn(1

12

)

In(6

62

)

In(6

22

)

In(8

20

)

V(2

13

)

Sn(2

21

)V

(22

1)

V(4

11

)

V(3

01

)

In(4

11

)S

n(1

01

)

Sn(2

11

)/C

(10

2)

Sn(1

10

)/C

(00

2)

In

ten

sity

(arb

. u

nit)

2 degree

2fs

139

crystalline phase of Tin Oxide. The crystalline size (D) of the composite‟s was estimated

using the Debye Scherrer equation as follows [5].

Table 5.5 Structural parameters of sonicated Indium and Vanadium doped Tin Oxide: MWCNT

composite

Treatments h k l 2θ(deg) d(A◦) FWHM D (nm) a(Ǻ)

Sonication

1 1 0

1 0 1

2 1 1

26.3956

33.7312

51.7539

3.37387

2.65504

1.76496

1.92880

1.56830

1.96500

04

05

04

a=4.7

c=3.1

Table 5.6 Dislocation density and strain of sonicated Indium and Vanadium doped Tin Oxide:

MWCNT composite


density (δ)

(x1015

)

Strain (ε)

(x10-3

)

Sonication

6

4

6

7.30

6.46

6.74

140

5.3.(a) SEM images of as-prepared Indium and Vanadium doped Tin Oxide: MWCNT

composite

Fig. 5.4 SEM image of Indium and Vanadium doped Tin Oxide: MWCNT

composite for a magnification of 10000 times


141




The above SEM images pictures morphology of the active layer deposited on the

surface of MWCNT. The images indicate the presence of metal oxide grains and CNT. On

higher magnification in the order (x30, 000), it is clear that the metal oxide active layer is

well coated on the surface of CNT. The diameter of the Tin Oxide: MWCNT hybrid was

obtained to be 40 nm and 48 nm.

5.3.(b) SEM images of microwave assisted Indium and Vanadium doped Tin Oxide:

MWCNT composite

The SEM images of microwave assisted composite were recorded in order to observe

the morphology of the active metal oxide film deposited on the surface of MWCNT. The

images at low magnification shows the metal oxide matrix in which the presence of CNT was

not revealed. On further magnification, it is clear that the metal oxide active layer is well

coated on the surface of CNT [6] due to impact of microwave irradiation on the sample. The

142

diameters of the Tin Oxide:MWCNT hybrid by SEM analysis were obtained to be 33 nm and

38 nm.





143



5.3.(c). SEM images of sonicated Indium and Vanadium doped Tin Oxide: MWCNT

composite



144





145

The SEM images of sonicated composite recorded the morphology of the metal oxide

film deposited onto MWCNT surface. The diameter of the Tin Oxide: MWCNT hybrid by

SEM analysis was obtained to be 33 and 40 nm.

5.4 TEM images of Indium and Vanadium doped Tin Oxide: MWCNT composite

Fig. 5.13 TEM image of Indium and Vanadium doped Tin Oxide: MWCNT

composite for a magnification of 100 nm

146





147





148



5.5 Elemental composition of Indium and Vanadium doped Tin Oxide: MWCNT

composite

Fig. 5.19 Elemental compositions of as-prepared Indium and


149

Fig. 5.20 Elemental composition of microwave assisted Indium and


Fig. 5.21 Elemental composition of sonicated Indium and


150

200 400 600 800 1000

0.5

1.0

1.5

2.0

2.5

AB

SO

RB

AN

CE

WAVELENGTH(nm)

uv 2f

200 400 600 800 1000

0.5

1.0

1.5

2.0

2.5

3.0

3.5

AB

SO

RB

AN

CE

WAVELENGTH(nm)

uv 2fm

The EDS spectrum (Fig. 5.19, 5.20, 5.21)) of Indium and Vanadium doped Tin Oxide:

MWCNT composite shows the presence of Tin, Indium, Vanadium, and Carbon and oxygen.

This confirms the existence of Indium Vanadium doped Tin Oxide onto MWCNT surface.

5.6. UV absorption spectrum of Indium and Vanadium doped Tin Oxide: MWCNT

composite

Fig. 5.22 UV absorption spectrum of as-prepared Indium and


Fig. 5.23 UV absorption spectrum of microwave assisted Indium

and Vanadium doped Tin Oxide: MWCNT composite

151

200 400 600 800 1000

0.5

1.0

1.5

2.0

2.5

AB

SO

RB

AN

CE

WAVELENGTH (nm)

uv 2fs

Fig. 5.24 UV absorption spectrum of sonicated Indium and


Fig. 5.25 indicates the comparative UV absorption of as-prepared, microwave

assisted, sonicated Indium and Vanadium doped Tin Oxide: MWCNT composite. The

absorption peak exists around 296 nm. The absorption curves of microwave assisted and

sonicated samples shifted to longer wavelength (red shift). The intensity of the microwave

assisted and sonicated samples are greater than the as-prepared sample indicating the

improvement in the degree of crystalline when compared to the as-prepared sample. The

improvement in the crystalline increases the gas sensing property of the sample. Compared

to as-prepared sample, microwave assisted sample has the advantage of short reaction time

with the adsorbing gas, small particle size, and narrow particle size distribution [7-9].

152

0 500 1000 1500 2000 2500

170

175

180

185

190

195

200

205

210

215

2f

GD

inte

nsity (

a.u

)

Raman shift (cm-1)

Fig. 5.25 Comparative UV absorption spectrum of

as-prepared, microwave assisted, sonicated Indium and


5.7. Laser-Raman spectrum of Indium and Vanadium doped Tin Oxide: MWCNT

composite

Fig. 5.26 Laser Raman spectrum of as-prepared Indium and


200 400 600 800 1000

0.5

1.0

1.5

2.0

2.5

3.0

3.5

f2 uv

microwave assisted

Sonicated

As-prepared

Ab

so

rba

nce

Wavelength(nm)

153

Fig 5.26 indicates the laser Raman spectrum of as-prepared Indium and Vanadium

doped Tin Oxide: MWCNT composite. The peak featured at 496 cm-1

, 648 cm-1

represents

the mode due to evidence of MWCNT with high purity and thin innermost layers, presence of

disordered amorphous Carbon respectively. The peak featured at 1345 cm-1

corresponds to

the D-band [10] and the peak at 1579 cm-1

represents the G-band produced due to the

tangential vibration of graphitic Carbon. The value of ID/IG for this sample is calculated to be

1.19. From the ratio of the intensities of D-band to G-band generically confirm the

assumption that graphite has a higher degree of crystalline order than MWCNT having

structural defects [11].

Fig. 5.27 Laser Raman spectrum of microwave assisted Indium


Fig. 5.27 indicates the laser Raman spectrum of microwave assisted Indium and

Vanadium doped Tin Oxide: MWCNT composite. The peak at 1341 cm-1

and 1579 cm-1

corresponds to the D-band and G-band respectively. The minor peaks around 1230 cm-1

depend strongly on the structural integrity of the Carbon nanotube. The relative intensities of

D-band to G-band (ID/IG) for the sample are calculated to be 1.14, which is less than as-

prepared Indium and Vanadium doped Tin Oxide: MWCNT composite.

0 500 1000 1500 2000 2500

170

180

190

200

210

220

230

240

250

2fm

GD

inte

nsity

(a.u

)

Raman shift (cm-1)

154

0 500 1000 1500 2000 2500

170

180

190

200

210

220

230

240

250

2fs

GD

inte

nsity

(a.

u)

Raman shift (cm-1)

Fig. 5.28 Laser Raman spectrum of sonicated Indium and


Fig. 5.28 indicates the laser Raman spectrum of sonicated Indium and Vanadium

doped Tin Oxide:MWCNT composite. The peak at 485 cm-1

shows the quality of the

MWCNT, it indicates the purity of the sample. The peak at 669 cm-1

and 1347 cm-1

corresponds to the laser irradiance and D-band of the sample. The peak featured at 1574 cm-1

indicates the G-band. The ratio of intensity of D-band to G-band for sonicated sample is

calculated to be 1.02.

5.8. Photoluminescence studies of Indium and Vanadium doped Tin Oxide: MWCNT

composite

Fig. 5.29 Photoluminescence of as-prepared Indium


300 400 500

0

2000000

4000000

6000000

8000000

10000000

f2pl

Inte

nsity

(a.u

)

wavelength(nm)

155

300 400 500 600

1000

2000

3000

fm2pl

In

ten

sity

(a.u

)

wavelength(nm)

Fig. 5.29 represents the photoluminescence spectra of as-prepared Indium and

Vanadium doped Tin Oxide: MWCNT composite. The PL spectra showed the emission

bands at 420 and 440 nm respectively.

Fig. 5.30 Photoluminescence of microwave assisted Indium and


Fig. 5.30 represents the photoluminescence spectra of microwave assisted Indium

Vanadium doped Tin Oxide: MWCNT composite. The emission bands at 420 and 440 nm

were observed in the PL spectra. The basis of the peak at 422 nm can be ascribed to the

luminescence centers found by tin interstitials or dangling bonds present in the tin Oxide

films [12]. The peak appearing at 474 nm correspond to the blue luminescence and can be

attributed to singly charged oxygen vacancies in the film [13, 14].

156

Fig. 5.31 Photoluminescence of sonicated Indium and


Fig. 5.31 represents the photoluminescence spectra of sonicated Indium and

Vanadium doped Tin Oxide sample. The PL spectra exhibited the emission bands at 406,

435, 471, 512, 555, and 588 nm respectively. The band around 400 corresponds to all the

luminescence centers such as nanocrystal and defects in the sample [15]. The band at 435

nm is attributed to the Tin interstitial present in Tin Oxide [16]. The band around 471 nm

corresponds to the blue luminescence and is attributed to the singly charged oxygen

vacancies in the sample [17]. The band at 555 nm is associated with defect energy levels

within the band gap of Tin Oxide. Oxygen vacancies are well known to be the most common

defects in Oxides and usually act as radiative centers in luminescence processes. Thus, the

nature of the transition is tentatively ascribed to oxygen vacancies, Tin vacancies, or Tin

interstitials, which form a considerable number of trapped sites within the band gap [18].

The oxygen vacancies are the intrinsic defects in n-type Tin Oxide and can capture electrons

and thus form ionized vacancies. The ionized vacancies can act as deep defect donors and

result in new energy level, which further influences the optical properties of Tin Oxide

nanoparticles [18].

300 400 500 600

1000

2000

3000

4000

fs2pl

Inte

nsi

ty(a

.u)

Wavelength(nm)

157

5.9 Gas sensing studies of Indium and Vanadium doped Tin Oxide: MWCNT composite

Fig. 5.32 Variation of electrical resistance of as-prepared Indium and Vanadium

doped Tin Oxide: MWCNT composite on exposure to 100 ppm CO2

Fig. 5.33 Variation of electrical resistance of as-prepared Indium and Vanadium


158

Fig. 5.34 Variation of electrical resistance of microwave assisted Indium Vanadium


Fig. 5.35 Variation of electrical resistance of microwave assisted Indium and

Vanadium doped Tin Oxide: MWCNT composite on exposure to

200 ppm CO2

159

Fig. 5.36 Variation of electrical resistance of sonicated Indium and Vanadium


Fig. 5.37 Variation of electrical resistance of sonicated Indium Vanadium

doped Tin Oxide composite: MWCNT on exposure to 100 ppm CO2

160

The figures 5.32, 5.33, 5.34, 5.35, 5.36, 5.37 depicts the variation of resistance of

Indium and Vanadium doped Tin Oxide: MWCNT composites. All the composites exhibited

a decrease in resistance on exposure to CO2 gas (100 and 200 ppm). The decrease in

resistance was found to increase when the concentration of gas increases. Resistance of a Tin

Oxide: MWCNT based gas sensor decreased in air because of the semiconducting nature.

Response towards Carbon dioxide exposure also decreased with increase in working

temperature, due to less absorption of Carbon dioxide to the sensor surface at high

temperature [19]. This work had confirmed the long response [20] i.e., variation in resistance

of the composite on exposure to CO2 gas at room temperature. The resistance decreased with

reducing gas exposure, implied that CO2 behave as a reducing gas [21, 22]. The fall in the

resistance was found to increase on exposure to 200 ppm than 100 ppm [23]. The reaction

between CO2 and oxygen species chemisorbed on the SnO2 surface prior to CO2 exposure

release electron trapped by the adsorbed oxygen species into SnO2 matrix, resulting in the

resistance decrease [24, 25].

Table 5.7 Sensing parameters for Indium and Vanadium doped Tin Oxide: MWCNT

composite on exposure to 100 ppm CO2

Treatment ΔR(Ω) Response time (s) Recovery time (s)

As-prepared 21 51 42

Microwave irradiation 185 141 129

Sonication 120 75 131

Table 5.8 Sensing parameters for Indium and Vanadium doped Tin Oxide: MWCNT

composite on exposure to 200 ppm CO2

Treatment ΔR(Ω) Response time (s) Recovery time (s)

As-prepared 34 61 47

Microwave irradiation 187 176 135

Sonication 135 97 150

It has been reported in the case of hybrid films, two depletion layers (and associated

potential barriers) co-exist [26, 27]; one of the depletion layer situated at the surface of the

grain of the Tin Oxide film and the other at the interface between MWCNT and Tin Oxide

film. Since Tin Oxide films behaves as n-type semiconductor and MWCNT behaves as p-

type semiconductor [28, 29], it is suggested that a heterostructure is developed at the

interfacing surface between Tin Oxide and Carbon nanotubes. The results indicate that,

addition of metal nanoclusters or metal nanoparticles onto the CNT surface played a

161

fundamental and major role in improving the gas-sensing parameters. Novel research are

being done to analyse the presence of metal clusters or nanoparticles at the CNT surface act

reducing the potential barrier of the depletion layers and enhance the specific gas adsorption,

thereby improving the selectivity or enhancing chemical reactions occurring at the surface.

The sensitivity of the hybrid film derived from the adsorption of CO2 at the Tin

Oxide surface changes the depletion layer present at the surface of the grain and also at the

Tin Oxide/MWCNT heterostructure [29]. As a result of these combined effect there occurs

an improvement in response of Tin Oxide-based hybrid sensors when compared to pure Tin

Oxide or metal-decorated CNT based gas sensors [30]. The results obtained in this work

confirm that amount of CNT added to the Tin Oxide matrix has to be extremely small as

reported in earlier works. A slight variation in decrease in resistance was found when the

concentration of the exposed gas was increased indicating that the response was

concentration dependent [31]. The best results were obtained with SnO2:MWCNT hybrids

and are in concordance with the results published by Wei et al [26]. The hybrid sensor

possessed good sensitivity to low trace (100 ppm and 200 ppm) of Carbon dioxide gas at

room temperature [32].

162

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chapter v preparation and characterization of...

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