chapter iv synthesis and characterization of floral

CHAPTER IV

SYNTHESIS AND CHARACTERIZATION OF

FLORAL AND ROD LIKE

CuO NANOPARTICLES

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4.1 Introduction

The fabrication of transition metal oxides with nanostructure

has been the target of scientific interests in recent years because of

their unique properties and fascinating applications in optoelectronics

and biomedical science. Along this line, synthesis of copper

nanoparticles with smaller sizes based on simple chemical reduction

is highly demanded. Copper is a highly conductive, much cheaper,

and industrially widely used material and it is uniquely with the

chemical reactivity capable of serving as precursors for the fabrication

of conductive structures for ink-jet printing [2] or forming CuInSe2 or

CuInxGa1-xSe2 semiconducting nano materials for photo detectors and

photovoltaics [3]. Copper oxide / copper (II) oxide / cupric oxide is a

semiconductor compound with a monoclinic structure. CuO has

attracted particular attention because it is the simplest member of the

family of copper compounds and exhibits a range of potentially useful

physical properties such as high temperature superconductivity,

electron correlation effects and spin dynamics. As an important p-type

semiconductor, CuO has found many diverse applications in various

devices such as gas sensors, photovoltaic cells, batteries and high

temperature superconductors etc. In the energy-saving area, energy

transferring fluids filled with nano CuO particles can improve fluid

viscosity and enhance thermal conductivity. CuO crystal structures

possess a narrow band gap, giving useful photo catalytic or

photovoltaic properties as well as photoconductive functionalities [4].

Limited information on the possible antimicrobial activity of nano CuO




72

is available. CuO is cheaper than silver, easily mixed with polymers

and relatively stable in terms of both chemical and physical

properties. Highly ionic nanoparticulate metal oxides, such as CuO,

may be particularly valuable antimicrobial agents as they can be

prepared with extremely high surface areas and unusual crystal

morphologies [5]. The materials like copper, silver, zinc present high

antibacterial activity, low toxicity, chemical stability, long lasting

action period and thermal resistance compared to organic

antibacterial agents [6]. In the present study, floral nano CuO and

CuO nanorods were synthesized by solution combustion method using

glycine and citric acid as fuel.

4.2 Result and discussion

4.2.1 Structural studies

The X-ray diffraction pattern of the CuO is shown in Figure.4.1.

The XRD peak positions were consistent with the Copper oxide and

the sharp peaks of XRD indicate the crystalline nature. For glycine

assisted CuO nanoparticles (CG) the peaks were observed at 2 =

32.39º, 35.40º, 38.62º, 48.65º, 53.30º, 58.10º, 61.44º, 65.68º, 66.17º,

67.93º, 72.30º and 74.99º and for citric acid assisted CuO

nanoparticles (CCA) the peaks were observed at 2 = 32.40º, 35.41º,

38.63º, 48.66º, 53.37º, 58.17º, 61.44º, 66.10º, 67.89º, 72.28º and

75.01º which correspond to (110), ( 110), (111), ( 202), (020), (202),

( 113), ( 311), (113), (311) and (004) Bragg�s reflections of monoclinic

structure of CuO respectively (JCPDS:80-1916). The lattice constant




73

values are also calculated and are very close to the standard data.

The calculated lattice constants of the unit cells are a=4.696 Å,

b=3.432 Å and c= 5.132 Å having =99.53º for CCA and a=4.694 Å,

b=3.432 Å and c= 5.134 Å having =99.51º for CG. The volume of the

cell is calculated to be 81.60 Å3 and 81.59 Å3 for CCA and CG

respectively. The samples exhibit smaller cell volumes than that of

bulk.

The XRD line width can be used to estimate the size of the

particle by using the Debye�Scherrer formula. It is commonly

accepted that XRD line broadening may be the result of pure size, or

micro strain, or both size and microstrain broadening. The W-H

approach considers the case when the domain effect and lattice

deformation are both simultaneously operative and their combined

effects give the final line broadening FWHM ( ), which is the sum of

(grain size) and (lattice distortion) [7]. This relation assumes a

negligibly small instrumental contribution compared to the sample-

dependant broadening. The results of the W-H analysis for CG and

CCA are shown in Figure.4.2. The plot showed a negative strain and is

found to have the value -0.002 for CG and -0.003 for CCA. This strain

is maybe due to the lattice shrinkage that was observed in the

calculation of lattice parameters. The main contribution for the strain

may arise from the chemical reaction and synthesis parameters such

as temperature, pressure and time factor.

However, the strain arising from these contributions as

calculated from the W-H model is very small and has negligible effect




Fig

gure.4.1 X

( 1

XRD patte

110) and (

ern of nan

(111) plan

no CuO (in

nes)

nset: zoommed view

of




Figure.4.

.2 W-H annalysis for

r a) CG annd b) CCAA.




74

on peak broadening [7]. The average crystallite size of the CuO

nanorods is found to be around 10 nm and these values are in good

agreement with that obtained from the Debye-Scherer�s equation and

HRTEM image observation value. The average crystallite size of floral

CuO is found to be 20 nm and this value is in good agreement with

the obtained Debye-Scherer�s equation. But the nano petals are

observed in the range of 40 nm thickness (HRTEM).

4.2.2 Morphological studies

The morphology, size and microstructure of the products were

investigated in detail through FESEM and HRTEM. Figure.4.3 (a)

shows the FESEM image of the floral CuO nanostructures. The

product consists of a large quantity of flower like microstructures in

2-5 m in size. Figure 4.3 (b) shows a detailed view of a single flower

CuO which clearly shows that the sample composed of many closely

packed wide nanosheets. Figure.4.3 (c) shows a typical image of wide

nanosheets that having width about 0.5 m and thickness about 40

nm at a higher magnification. It is found that the CuO nanostructures

are composed of several thousands of sheets like petals having tips

projected outward with comparable lengths having a common wider

base and which thus form a spherical flower like structure. The

typical length of one petal is identified as 650 nm, while the widths of

the bases and tips are in the range of 360 nm and 120 nm

respectively. For detailed structure observations, the products were

further characterized by HRTEM shown in Figure.4.3 (d). It represents




75

the morphology of the flower like CuO micro/nanostructures, which

reveals that the CuO flower is composed of wide nanosheets and inset

shows the SAED pattern of floral CuO. Figure.4.3 (e) shows the

nanoflower with regular spacing of clear lattice planes. This lattice

spacing is found to be 0.142 nm which corresponds to (022) planes of

monoclinic structure of floral CuO.

Figure.4.4 shows the FESEM image of CuO nanorods. Figure 4.5 a)

shows the HRTEM images of CuO nanorods and these nanorods were

observed to be around the width of 10-20 nm which coincides with the

particle size calculated from XRD. The diameter of the CuO nanorod is

about 20-25 nm and having various lengths range from 100-250 nm.

Figure 4.5 b) shows the nanorod (the arrowed area in Figure 4.5 a))

with regular spacing of clear lattice planes. This lattice spacing is

found to be 0.157 nm which corresponds to (202) planes of monoclinic

structure of CuO nanorod and inset shows the SAED pattern of

nanorod CuO. Figure 4.5c) shows the energy dispersive spectra of the

copper nanorods. It confirms the presence of copper oxide.

Studying the growth mechanism of nano CuO, it is possible to

suggest that the organic fuel (glycine & citric acid) is responsible for

the formation of the CuO nano flower and rod due to the easier

complex formation. When citric acid is employed, the heat released in

combustion is more and as a result the combustion enthalpy is more

which is responsible for the growth of the sample and complete

combustion reaction with more crystalline phase. In the case of

glycine, it has been observed that the powder of the combustion




Figure 4

detailed v

of wide n

4.3 FESEM

view of an

anosheets

M image

n individu

s

of (a) the

ual flower

e floral Cu

r like nan

uO nanos

ostructur

structures

re and (c)

s; (b) a

pieces




Figure 4

pattern o

lattice pla

4.3 HRTE

of floral C

anes and

EM image

CuO); (e) a

(f) Energy

e of (d) th

a nanoflo

y dispersi

he CuO n

ower with

on spectr

nanosheet

regular s

a of floral

ts (inset:

spacing o

l CuO.

SAED

of clear




Figure 4

4.4 The FEESEM imaage of CuuO nanoroods




Figure 4

arrowed

planes an

4.5 HRTEM

area in

nd c) Ener

M images

Figure 4.

rgy disper

s of a) Cu

.5a)) with

rsive spec

uO nanor

h regular

ctra.

ods; b) th

spacing

he nanoro

of clear

od (the

lattice




76

reaction has a morphology forming flower like network of

nanocrystalline CuO, which may be due to the rapid release of

gaseous byproducts during the combustion reaction. So the result

indicates that the presence of glycine/citric acid has a significant

effect on the morphology of the sample.

4.2.3 Vibrational studies

The purity and molecular structure of the product were

analyzed by FTIR spectroscopy. Figure 4.6 shows the FTIR spectrum

of CG and CCA which was acquired in the range of 400-4000 cm-1.

The peaks in the range 3100-3800 cm-1 are attributed to O-H

stretching vibration, which are assigned to small amount of H2O

existing (during pellet formation) in the nanocrystalline CuO. In the

case of CG, The peaks observed at 2267 cm-1, 1546 cm-1, are assigned

to NH3+ stretching vibration and a peak at 1177 cm-1 is assigned to

stretching vibration adsorption bands of carboxyl (C=O) groups. The

small peak at 598 cm-1 confirms the formation of CuO nanostructure.

The peak at 899 cm-1 is assigned to the C-C stretching mode. In the

case of CCA, the peak observed in the range 1532 cm-1 and 1188 cm-1

assigned to stretching vibration adsorption bands of carboxyl (C=O)

groups. The peak at 917 cm-1 is assigned to the C-C stretching mode

and the peak at 598 cm-1 is the characteristic peak of nano CuO.

4.2.4 Optical studies

UV- visible spectroscopic measurements were carried out at

room temperature to study the effect of CuO nanoparticles in the




Figure 4

4.6 FTIR sspectra of f CG and CCCA




Figure 4.

.7 a) The

b) Plot

UV- visib

of ( h )2 v

ble absorp

vs h of n

ption spec

nano CuO

tra of nan

O.

no CuO annd




77

range of 300-800 nm. The UV- visible absorption spectrum of nano

CuO sample is shown in Figure 4.7 a). There is a broad shoulder

around 296 nm and weak absorption peak at 570 nm for CCA and for

CG there is a broad shoulder around 302 nm and weak absorption

peak at 577 nm. CCA is shifted towards the lesser wavelength than

CG because of the size effect. The optical energy bang gap Eg of

samples was estimated using Tauc relation [9].

In general, the CuO nanoparticles have direct band gap energy

(Eg) (1.2 eV). From the figure 4.7 b), it is seen that the CCA and CG

samples are having the optical energy band gap of 3.05 eV and 2.9 eV

respectively. The blue shift of the direct band gaps displayed the effect

of the morphologies of crystals and may be due to the quantum size

effect. The microcrystals with different morphologies have different

dominant active facets and response different excitation energy and

consequently have different direct band gaps [10].

4.3 Conclusion

The copper oxide nanoflowers and nanorods were synthesized

by solution combustion method. The XRD pattern analysis showed

that floral and rod like CuO is having monoclinic crystal structure.

HRTEM and FESEM confirm the shape of floral CuO and CuO

nanorods. The optical energy band gap was calculated using the UV-

visible absorption spectra and it was found to be 3.05 eV for CCA and

2.9 eV for CG.




78

References

[1] P. Sharma, G.S. Lotey, S. Singh, N.K Verma, J. Nanopart. Res.,

13(2011) 2553.

[2] S. Jeong, K. Woo, D. Kim, S. Lim, J.S. Kim, H. Shin, Y. Xia, J.

Moon, Adv. Funct. Mater., 18(2008)679.

[3] J. Tang, S. Hinds, S.O. Kelley, E.H. Sargent, Chem. Mater.,

20(2008)690.

[4] G. Ren, Dawei Hu, EileenW.C. Cheng, Miguel A. Vargas-Reus,

Paul Reip, Robert Han-Xuan Zhang , Uwe Siegert , Ran Liu,

Wen-Bin Cai, Scale Res. Lett., 4(2009)705.

[5] P.K. Stoimenov, R.L. Klinger, G.L Marchin, K.J Klabunde,

Langmuir, 18(2002)6679.

[6] H.J. Lee, S.Y. Yeo, S.H. Jeong, J. Mat. Sci., 38(2003)2199.

[7] R. Yogamalar, R. Srinivasan, A. Vinu, K. Ariga, A.C. Bose, Solid

State Comm., 149(2009)1919.

[8] J. Tauc (ed.), Amorphous and liquid semiconductor, (1974),

Newyork, Plenum Press.

[9] Q. Zhu, Y. Zhang, J. Wang, F. Zhou, P. K. Chu, J. Mater.

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