chapter iv synthesis and characterization of floral
TRANSCRIPT
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
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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
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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
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Fig
gure.4.1 X
( 1
XRD patte
110) and (
ern of nan
(111) plan
no CuO (in
nes)
nset: zoommed view
of
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Figure.4.
.2 W-H annalysis for
r a) CG annd b) CCAA.
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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
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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
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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
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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
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Figure 4
4.4 The FEESEM imaage of CuuO nanoroods
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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
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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
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Figure 4
4.6 FTIR sspectra of f CG and CCCA
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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
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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.
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