chapter 4 synthesis and characterization of magnisium...

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Chapter 4

SYNTHESIS AND CHARACTERIZATION OF MAGNISIUM OXIDE-

TRANSITION METAL OXIDE NANOCOMPOSITES

This Chapter contains the detailed description of synthesis of MgO-X (X= Transition

metal oxide) nanocomposites by using Co-precipitation method and then samples have

been calcined at 6000C for duration 4 hrs and 6 hrs and characterized by using various

characterization techniques. The results are discussed in this Chapter.

4.1. IntroductionToday nanoparticles play key role in advance technology. However, nanoparticles

have limited applications and to increase their functionality , nanocomposites come in to

picture. The composite material is a mixture consisting of at least two phases of different

chemical compositions. The physical properties of nanocomposites can be combined to

produce new material of desired response. Optical and magnetic properties of

nanocomposites change when particle size changes (in nano scale). Composites have

excellent properties such as large hardness, high melting point, low density, low

coefficient of thermal expansion, high thermal conductivity, good chemical stability and

improved mechanical properties such as higher specific strength, better wear resistant and

specific modulus and are condidates potential for various industrial applications [1-3].

Nanomaterials exhibit properties different from those of the bulk material and these

properties depend on their size and method of synthesis. The transition metal oxide

nanomaterials are of great technological importance because of their valance d-orbitals.

Magnesium Oxide (MgO) is an exceptionally important material for its wide range of

applications as antibacterial properties, fire-retardant, uv-protection, dental cement,

catalysis, paints, refractory materials superconductor physics and so on[4-6]. A lot of work

posibilty in research on the synthesis of Magnesium Oxide nanoparticles and on its

nanocomposites .

In recent years, nickel oxide nanoparticles has attracted much interests due to its novel

optical, electronic, magnetic, thermal, mechanical properties[7-8] and potential

application in catalyst, gas sensors, electrochemical films, photo electronic devices and in

battery electrodes [8-9]. Nickel oxides are used as electrode materials in super capacitors

due to their high electrochemical reaction activity and nano-structured electrode materials

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show better performances than traditional materials because of the distance within the

material over which electrolyte ions transport is shorter [10].

The unique property of CuO is its semiconducting nature and of their great practical

importance in fabrication of microelectronic and optoelectronic devices, such as electro

chemical cell, gas sensors, magnetic storage devices, antibacterial ointment , high-critical

temperature superconductors and catalysts[11] etc. Due to the potential application of

CuO, it acts as a catalyst; whereas many other metal oxides are not used for the catalytic

activity. As like Fenton’s reagent CuO combined with another metal oxide like CeO2, is

used in waste water treatment [12]. CuO is used as supercapacitor in Electrical

applications [13]. It has the wide band gap nearly equal to ZnO in nano range. The band

gap of CuO makes it useful for solar energy conversion and it can be used for production

of solar cell [14], CuO nano fluids can acts as a coolants in refrigerators[15]. CuO can be

used as coolant material and it can control effectively the temperature of other coolants

like TiO2, alumina and silver nanoparticles [16] etc.

Among the various forms of iron oxides, maghemite (γ-Fe2O3) and hematite (α-

Fe2O3) are of great importance in technological and industrial applications. Maghemite

has numerous applications like recording, memory devices, magnetic resonance imaging,

drug delivery or cell targeting [17]. Hematite exhibits high resistance to corrosion,

therefore, it has been extensively used in many fields which include photo-anode for

photo assisted electrolysis of water [18]. It is an active component of gas sensors,

catalyst, lithium ion battery, pigments and oxidizer in thermite composition [19]. It is

also used in magnetic fluids, also called ferro fluids, for damping in inertial motors, shock

absorbers, heat transfer fluids etc [20].

Magnetic nanoparticles such as Co3O4 have been important applications in catalysis,

ferro-fluids , high-density recording media , microwave absorbing materials [21] etc.. In

nano scale it was observed that the quantum confinement effect was a lot of influence on

the material optical properties.

4.2 Samples investigatedConsidering the above facts the following series of samples were prepared by adding

various transition metal oxides with different concentrations to MgO samples.

1. The first series comprises MgO-NiO nanocomposites with different concentration

of NiO ( 5%, 10%, 15%).

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2. The second series consist of MgO-CuO nanocomposites with different

concentration of CuO ( 5%, 10%, 15%).

3. The third series comprises MgO-Fe2O3 nanocomposites with different concentration

of Fe2O3 ( 5%, 10%, 15%) .

4. The fourth series consist of MgO-Co3O4 nanocomposites with different

concentration of Co3O4( 5%, 10%, 15%).

4.3 Experimental Techniques4.3.1 Sample Synthesis Technique

There are many synthesis techniques were described in Chapter-2 and the co-

precipitation technique was used in the present work for the synthesis of samples, which is

described below:

(a ) MgO-NiO nanocomposite

All the starting chemicals used in the present work were of analytical grade. Solution

of 1M of MgCl2.6H2O (HIMEDIA, India) and appropriate concentration of

Ni(NO3)2.6H2O( HIMEDIA, India) was prepared in 100 ml of de-ionized water. Then

NH4OH solution was poured in the above solution at 1000C and the resulting mixture was

constantly stirrered for 2 hrs by using magnetic stirrer. The resulting mixture was kept for

ageing at the room temperature for 24 hrs. After the reaction, the resulting green

precipitates were filtered and washed with de-ionized water and subsequently with ethanol

(Merck) for several times to remove the by-products or impurities. The filtered cake was

dried in air at 100°C for 4hr. The as-synthesized samples of different concentrations were

calcined in air for different time duration and at fixed temperature in air. Now the sample

were crushed in agate mortar to obtain MgO-NiO nanocomposites fine powder. Which

were used for further characterization. It was found that the intensity of most intense peak

in XRD increases, when durations of calcination from 4hrs and 6hrs and calcined at 6000C for so indicating good crystallanity of nanomaterials and beyond this range the value of

intensity of most intense peak in XRD become more or less constant indicating

stabilization of structure [20].

As discussed Chapter-3, the optimum value of calcination temperature for MgO

nanoparticles was 600 0C and was ,therefore, used for the present samples of

nanocomposites. In order to see the effect of time duration, it has varied from 4 hrs to 6

hrs.

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(c) MgO-CuO nanocomposites

The appropriate amount of MgCl2.6H2O (HIMEDIA, India) and Cu(NO3)2.6H2O(

HIMEDIA, India) were mixed in 100 ml of de-ionized water and the remaining process is

same as discussed in previous MgO-NiO nanocomposites.

(c) MgO-Fe2O3 nanocomposite

In the synthesis of MgO-Fe2O3 nanocomposite the co-precipitation method is used,

as discussed earlier. However the solution of appropriate amount of MgCl2.6H2O

(HIMEDIA, India) and Fe(NO3)3.9H2O ( HIMEDIA, India) were used in 100 ml of de-

ionized water and other condition of synthesis and calcination are same as discussed in

synthesis of MgO-NiO nanocomposites .

(d) MgO-Co3O4 nanocomposite

In the synthesis of MgO-Co3O4 nanocomposite the co-precipitation method is used,

as discussed earlier. However the solution of appropriate amount of MgCl2.6H2O

(HIMEDIA, India) and Co(NO3)2.6H2O ( HIMEDIA, India) were used in 100 ml of de-

ionized water and other condition of synthesis and calcination are same as discussed in

synthesis of MgO-NiO nanocomposites .

4.3.2 Characterization Techniques

The MgO-X (X= NiO, CuO, Fe2O3, Co3O4) nanocomposites were analyzed by XRD

using a PANalytical X’Pert-Pro powder diffractometer with CuKα radiation (λ = 1.5406Å).

The variations of lattice parameters, crystalline size were studied by using XRD

techniques. FTIR spectra were recorded on a Perkin Elmer RX FTIR spectrometer. FTIR

helps to study transmittance and purity of samples.The morphology of the MgO-NiO

nanocomposites was studied by using JSM-6360 JEOL TEM. The band gap energys of

nanoparticles were determined by using absorption graph recorded from Hitachi 330

double beam UV-visible spectrophotometer. The size and morphology of the

nanocomposites were also observed from images recorded from Scanning Electron

Microscope (SEM, Model JSM−6700).The details of experimentation are described in

Chapter-2 and results obtained are discussed below for each of the series.

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4.4 Results and Discussion

4.4.1 Characterization of MgO-NiO nanocomposites4.4.1.1 X-ray Diffraction (XRD) studies

X-ray powder diffraction (XRD) studies have been carried out to determine the

structure (crystallinity) using X-ray diffractometer with Copper (kα) radiation (λ =

1.5418 Å) in the range of 100–800. The typical XRD patterns of MgO-NiO(10%)

nanocomposites calcined for different duration of time (4 hrs and 6 hrs) at fixed

temperature (600 0C) are shown in Figure 4.1 and XRD pattern of MgO nanoparticles

calcined at 600 0C for 4hrs and 6hrs are also reproduced (from Chapter-3) in Figure 4.1

for comparison purpose. Effect of variation of concentration of NiO in XRD peaks are

exhibited in Figure 4.2

Figure 4.1 XRD patterns of MgO-NiO(10%) nanocomposites calcined at 6000C for(a) 4 hrs (b) 6 hrs and MgO nanoparticles calcined at 6000C for (c) 4 hrs (d) 6 hrs

XRD peaks of MgO appears at 2θ~ 37.140, 43.110, 62.470, 74.900, 78.780 (as

described in Chapter-3). The major peaks for NiO nanoparticles are reported to be at

2θ~37.2800, 43.2300 and 63.200, as per the JCPDS card no. 78-043. The peaks at 38.50 ,

43.110,62.450 and 78.00 appear to be merged in the peaks of MgO corresponding to

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position at 37.060, 43.040, 62.440 and 78.720 in nanocomposites. On addition of NiO the

in MgO samples the position of peak does not change significantly. However, the width of

the peaks changes with increases the concentration of NiO in the samples. Crystallite size

of nanocomposites samples were estimated by Debye-Scherrer’s equation (as discussed in

Chapter-2).

D = 0.9 λ / β cosθ

where D is the crystallite size, λ is the wavelength of X-ray beam, β is the full width

at half maximum of the most intense peak, and 2θ is the Bragg diffraction angle of the

maximum intense peak. The obtained values of β and D are presented in Table 4.1.

Table 4.1 XRD data for β and D of MgO nanoparticles and MgO-NiO nanocomposites

calcined at a temperature 600 0C for different durations (4hrs, 6hrs)

Sr.No.

Name of sample Calcinationduration oftime

Position ofmost intensePeak(indegrees)

Value ofFWHM ofmost intensePeak (β)(inradian)

Crystallitesize (D)

1 MgO NPs 4 hrs 43.1164 0.4117 18.97 nm

2 MgO NPs 6 hrs 43.0396 0.4007 21.07 nm

3 MgO-NiO (5%) NCs 4 hrs 43.245 0.3873 21.77 nm

4 MgO-NiO (10%)NCs

4 hrs 43.0432 0.3676 22.95 nm

5 MgO-NiO (10%)NCs

6 hrs 43.0330 0.3509 24.03 nm

6 MgO-NiO (15%)NCs

4 hrs 43.139 0.2802 31.13 nm

The XRD patterns for MgO-NiO nanocomposites exhibit the XRD peaks both due to

MgO and NiO as per the JCPDS card no. 78-430 for MgO and JCPDS card no.78-043 for

NiO. Peak positions (2θ) of some of the peaks of MgO are at same or close to the peak

position of NiO and hence their intensity increases. The crystallite/particle size is observed

to increase on addition of NiO to MgO and with increase in the concentration of NiO in

MgO, goes on increasing: the crystallite size for MgO nanoparticles is 18.97 nm while for

MgO-NiO nanocomposites containing 5%, 10%, 15% NiO the size becomes 21.77nm,

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22.95 nm and 31.13 nm respectively (for all the samples calcined at 6000C for 4hrs). The

increase in crystallite size with addition of increasing concentration of NiO in MgO might

be due to the higher value of atomic radius (size) for Ni than that of Mg.

Figure 4.2 XRD patterns of MgO nanoparticles calcined at 6000C for (a) 4 hrs andMgO-NiO nanocomposites with different concentrations and calcined at 6000C for 4

hrs(b) MgO-NiO (5%) nanocomposites(c) MgO-NiO (10%) nanocomposites (d)MgO-NiO (15%) nano-composites

Perusal of the data presented in Figure 4.2 also shows that the crystallite size

increases with increase in calcination duration at fixed calcination temperature (6000C); it

is 22.95 nm for 4hrs calcination and 24.03 nm for 6hrs calcination for MgO-NiO(10%)

nanocomposites with increase in calcination time duration, the growth of crystal is

expected to improve while defects and imperfections decreases and hence crystallite size

is increased.

4.4.1.2 Fourier Transform Infrared (FTIR) Studies

FTIR Spectra of the MgO-NiO (5%,15%) nanocomposites calcined at 6000C for 4

hrs and 6 hrs are shown in Figures 4.3 and 4.4. Persual of the figure shows the IR broad

band at around 3407 cm-1 ,1471 cm-1, 1025 cm-1, 868 cm-1 , 667 cm-1 and which are at

same position as in IR spectra of MgO nanoparticles described in Chapter-3. An additional

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peak is observed at 496 cm-1 in Figure 4.3(A) and for seen their variation the magnified

image is reproduced in Figure 4.3(B). This peak is attributed to M-O-M vibration mode of

NiO present in the sample [23]. Peaks occurring in the range 400-1000 cm-1 in FTIR

spectrum confirmed the presence of pure MgO-NiO (5%,10%,15%) nanocomposites.

(A) (B)Figure 4.3 (A) FTIR Spectra of MgO-NiO nanocomposites with different

concentrations and calcined at 600 0C for 4 hrs(a) MgO-NiO(5%) nanocomposites(b) MgO-NiO(15%) nanocomposites and (B)same as (A) but magnified view with

different scale

FTIR Spectra of the MgO-NiO (10%) nanocomposites calcined at 6000C for 4 hrs and

6 hrs of prepared sample are shown in Figure 4.4. Perusal of the figure shows that

transmittance of the all calcined samples increases with increase in the duration of

calcination temperatures (from 4 hrs to 6 hrs), It might be due to the increase of the

condensation of the oxygen during calcination process.

Figure 4.4 FTIR Spectra of MgO-NiO (10%) nanocomposites calcined at 600 0C for(a) 4 hrs (b) 6 hrs

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4.4.1.3 UV-VIS Spectral studies

UV-VIS spectra of all the samples were recorded in the wavelength range 200 to

800 nm and for the UV–vis absorption measurement, the calcined MgO-NiO

nanocomposites samples are ultrasonically dispersed in absolute ethanol before

examination, using absolute ethanol as the reference sample. The recorded graph of

absorption coefficient versus wavelength of MgO-NiO (10%) nanocomposites calcined at

fixed temperature (600 0C) for different duration of time are shown in Figure 4.5. It has

been found that firstly the absorbance decreases with an increase in wavelength, and a

sharp decrease in absorbance near the band edge (367 nm) indicating the nanostructure

nature of the samples [24] thereafter the value of absorption coefficient are more or less

constant show the uniform size of synthesized materials.

Figure 4.5 Absorption graph MgO-NiO (10%) nanocomposites calcined at 600 0Cfor (a) 4 hrs (b) 6 hrs

The effect of variation of NiO concentration in absorption spectra were

examined in MgO-NiO (NiO 5%, 15%) nanocomposites for fixed duration of

calcination and at fixed calcination temperature and are shown in Figure 4.6. Perusal

of the figure shows that absorption value increases with increase of concentration

because crystallite size increases with dopant concentration from 5% to 10% and

absorption rate is depending on size of samples[25].

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Figure 4.6 Absorption graph MgO-NiO nanocomposites with different concen-trations and calcined at 600 0C for 4 hrs (a) MgO-NiO (5%) nanocomposites (b)

MgO-NiO(15%) nanocomposites

Tauc plot were used to determine the optical energy band gap of samples as shown in

figures 4.7(A) and 4.7(B) respectively and the band gap energy of MgO-NiO (NiO 5,

10%, 15%) nanocomposites are determined by using the transition rate equation for direct

band gap semiconductor. The absorption coefficient for direct transition is given by the

equation (as discussed in Chapter-3):

α(hv) = A(hv- Eg)n ……………………………………………(3.2)

where hv= photon energy, α= absorption coefficient

α=4πk/λ; k is the absorption index or absorbance, λ is the wavelength in nm, Eg is the

band gap energy. A= constant. For the present work, n= ½ corresponding to the allowed

direct transition was formed to hold and the corresponding Tauc plot are shown in Figures

4.7(A) and 4.7(B) respectively.

(A) (B)Figure 4.7 Tauc plot of(A) MgO-NiO nanocomposites with different concentrations

and calcined at 600 0C for 4 hrs (a) MgO-NiO(5%) nanocomposites (b) MgO-NiO(15%) nanocomposites (B) MgO-NiO(10%) nanocomposites calcined at 600 0C

for (a) 4 hrs (b) 6 hrs

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The value band gap of the calcined samples was determined from Tauc plots are

tabulated in Table 4.2. From Tauc plots it was found that all the transition were direct

allowed transition and value of energy band gap decrease as the duration of calcination

increases. It might be due to quantum confinement effect i.e. increase the crystallite size,

decrease the energy band gap, because the crystal lattice expands and the interatomic

bonds are weakened. Weaker bonds means less energy is needed to break a bond and get

an electron in the conduction band [26].

The Tauc plots of MgO-NiO(10%) nanocomposites for different concentration for

fixed duration of calcination at fixed temperature (600 0C) is shown in Figure 4.7(A) and

Perusal of Figure 4.7(A) shows that value of band gap energy increases with increase of

dopant concentration. The values of band gap of calcined samples calculated from Tauc

plot is tabulated in Table 4.2.

Table 4.2 Optical Band Gap of MgO nanoparticles and MgO-NiO nanocomposites

calcined at 600 0C for different duration of calcination

Sr.No.

Name of sample Duration of calcination Energy band( in eV)

1 MgO nanoparticles 4 hrs 4.6

2 MgO nanoparticles 6 hrs 4.1

3 MgO-NiO(5%) nanocomposites 4 hrs 4.0



6 MgO-NiO(15%) nanocomposites 4 hrs >6.0

4.4.1.4 Transmission Electron Microscopy (TEM) studies

TEM images of MgO-NiO nanocomposites calcined at 600 0C for 4 hrs and for

different concentration are shown in Figures 4.8(a) and 4.8(b) respectively. Perusal of the

figure shows the size of the nanoparticles from 15nm to 21.5nm and average crystallite

size comes out from these results is 19 nm. The TEM results are in accordance with those

of XRD results and verified that crystallite size increases with dopant concentration. From

images it was observed that particles are uniform in size, agglomerated in nature and

truncated spherical in shape.

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(a) (b)

Figure 4.8 TEM images of MgO-NiO nanocomposites with differen concentrationsand calcined at 600 0C for 4 hrs (a) MgO-NiO (10%) nanocomposites (b) MgO-NiO

(15%) nanocomposites4.4.1.5 Scanning Electron Microscopy (SEM) studies

The SEM images of MgO-NiO nanocomposites calcined at 600 0C for 4hrs and 6 hrs

were more or less similar to MgO nanoparticles, which is described in Chapter-3 and

typical SEM image of MgO-NiO nanocomposites calcined at 600 0C for 4 hrs is shown in

Figure 4.9. Perusal of Figure 4.9 show that particles are uniform in size, agglomerated in

nature and truncated spherical in shape.

Figure 4.9 SEM image of MgO-NiO (10%) nanocomposites calcined at 600 0C for4 hrs

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(a) (b)









90

(a) (b)









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4.4.1.6 Conclusions1. MgO-NiO nanocomposites of different concentration for have been prepared

successfully by Co-precipitation method. The crystallite size of calcined nanocomposites

samples of different dopant concentration were evaluated by using Debye-Scherrer

formula and it has been found that average crystallite size was increases with increases the

duration of calcination at fixed calcination temperature; it might be due to increases the

growth of crystals as the duration of calcination increases at fixed calcination temperature.

2. Perusal of XRD graph also show that crystallite size of nanocomposites increases

with increase of concentration of NiO in the samples for fixed duration of calcination and

at fixed calcination temperature because Ni atom having more atomic radius than MgO

atom.

3. Perusal of FTIR Spectra of calcined samples MgO-NiO (5%, 10%, 15%)

nanocomposites show that peaks band at 3407 cm-1, 1471cm-1, 1025 cm-1, 868 cm-1, 667

cm-1 are same as appeared in MgO nanoparticles which is discussed in Chapter-3 and an

additional peak is found at 496 cm-1 were due to presence of NiO in the sample i.e. M-O-

M vibration of NiO particles. So FTIR spectra confirm the synthesis and purity of MgO-

NiO nanocomposites.

4. The transmittance of calcined samples increases with increase of the duration of

calcination ( 4 hrs to 6 hrs) for fixed calcination temperatures. It might be due to the

increase of the condensation of the oxygen as the duration of calcination increases.

5. The energy band gap of calcined samples were determined by Tauc plot and it has

been found that all the energy bands are direct allowed energy bands and observed value

of energy band gap increase with increasing the dopant concentration and decreases with

increases the duration of calcination, it might be due to quantum confinement effect i.e. As

crystallite size of sample increases, the value of energy band gap decreases.

6. From absorption spectra, It has been found that the absorbance decreases with an

increase in wavelength, and a sharp decrease in absorbance near the band edge (200 nm to

320 nm) indicating the crystalline nature of the samples and particles are uniform in shape

and absorption increases with increases the time duration of calcination for fixed

temperature.

7. From absorption spectra, It has been found that the absorbance decreases with

increase the NiO dopant concentration in the sample for fixed duration of time at fixed

temperature of calcination.

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8. Perusal of TEM images of MgO-NiO nanocomposites shows that all the calcined

MgO-NiO nanocomposites were in the range of 15 nm to 21.5 nm and average particle

size is 19 nm , which isin accordance with XRD results. From TEM images it has been

observed that particles are spherical in shape and agglomerated in nature.

9. Perusal of SEM image of calcined sample of MgO-NiO nanocomposites shows that

particles are uniform and agglomerated in nature and spherical in shape.

4.4.2Characterization of MgO-CuO nanocomposites4.4.2.1 X-ray diffraction (XRD) Studies

X-ray powder Diffraction (XRD) studies were carried out to confirm the the structure

(crystallinity) using X-ray diffractometer with Copper (kα) radiation (λ = 1.5418 Å) in the

range of 100–800. The XRD patterns are shown in Figures 4.10and 4.11 respectively.

The XRD patterns of MgO-CuO nanocomposites calcined for different duration of

time (4 hrs and 6 hrs) at fixed temperature (600 0C) were shown in Figure 4.10 and

XRD patterns of MgO nanoparticles calcined at 600 0C for 4hrs is reproduced from

Chapter-3 for comparison purpose.

Figure 4.10 XRD patterns of (a) MgO nanoparticles calcined at 6000C for 4 hrs (b)MgO-CuO(10%) nanocomposites calcined at 6000C for 4 hrs (c) MgO-CuO (10%)

nanocomposites calcined at 6000C for 6 hrs

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described in Chapter-3). The major peaks for CuO nanoparticles are reported to be at

2θ~37.800, 43.2970, 50.4330, 74.1300 and at 78.110 as per the JCPDS card no. 80-1268.

The peaks at 38.50 , 43.110,62.450 and 78.00 appear to be merged in the peaks of MgO

corresponding to position at 36.980, 42.970, 62.330 for nanocomposites. The development

of addition peaks at 2θ~ 35.780, 38.820 and 74.760 in nanocomposites are due to the

presence of CuO in nanocomposites samples. Crystallite size is estimated by using Debye-

Scherrer’s equation

D = 0.9 λ / β cosθ

where D is the crystallite size, λ is the wavelength of X-ray beam, β is the full width

at half maximum of the most intense peak, and 2θ is the Bragg diffraction angle of the


Table 4.3 XRD data of MgO nanoparticles and MgO-CuO nanocomposites calcined at

6000C for different duration of calcination.

Sr. No. Name of sample Duration ofcalcination

Positionof mostintensePeak

Value ofFWHM ofmost intensepeak(β)

Crystallitesize(D)

1 MgO NPs 4 hrs 43.1164 0.4117 18.97 nm2 MgO- CuO (5%) NCs 4 hrs 43.119 0.2929 28.83 nm3 MgO-CuO (5%) NCs 6 hrs 43.101 0.2775 30.42 nm4 MgO-CuO (10%) NCs 4 hrs 42.9622 0.2836 29.74 nm5 MgO-CuO (10%) NCs 6 hrs 43.0290 0.2676 31.54 nm6 MgO-CuO (15%) NCs 4 hrs 43.049 0.2465 34.24 nm7 MgO-CuO (15%) NCs 6 hrs 43.113 0.2359 35.73 nm

Perusal of XRD patterns shown in Figure 4.10 show that peak of MgO and CuO

nanomaterials are nearly in same position which increase the intensity of peak of MgO

nanomaterials [27] and additional peaks were observed at position 2θ~ 35.780 ,38.820

which is corresponding to CuO peak confirm from JCPDS card no. 78-430 for MgO and

JCPDS card no.80-1268 for CuO. It shows that the presence of CuO in the MgO sample .It

is observed that the crystallite size of MgO-CuO nanocomposites increases with time

duration of calcination i.e. MgO-CuO( CuO 10%) nanocomposites calcined at 600 0C for

4hrs is 29.74 nm and for 6 hrs is 31.54 nm .It might be due to the growth of crystal

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improved and imperfection or defects in crystal decreases with increase the calcination

time duration. The crystallite size also increases from MgO nanoparticles calcined at 6000C for 4hrs i.e. 18.97 nm to MgO-CuO(10%) nanocomposites 600 0C for 4hrs i.e. 29.74

nm and similar results were obtained for other nanocomposites samples calcined for

different duration of time for fixed calcination temperature. The increase in crystallite size

with addition of increasing concentration of CuO in MgO might be due to the higher value

of atomic radius (size) for Cu than that of Mg [28].

The effect of variation of concentration of CuO in MgO-CuO nanocomposites for

fixed time duration of calcinations and for fixed temperature at 600 0C of XRD patterns is

shown in Figure 4.11.

Figure 4.11 XRD patterns of (a) MgO-CuO (5%) nanocomposites calcined at 6000Cfor 4 hrs (b) MgO-CuO (5%) nanocomposites calcined at 6000C for 6 hrs (c) MgO-

CuO (15%) nanocomposites calcined at 6000C for 4 hrs (d) MgO-CuO (15%)nanocomposites calcined at 6000C for 6 hrs.

Perusal of XRD patterns shown in Figure 4.2 shows that peak of MgO and CuO

nanomaterials are nearly in same or close position, which increase the intensity of peak of

MgO nanomaterials[27] and the position of other intense peaks are same as discussed

earlier as in nanocomposites calcined for different duration. The crystallite size of MgO-

CuO nanocomposites increases with concentration of CuO composition i.e. MgO-CuO(

CuO 5%) nanocomposites calcined at 600 0C for 4hrs is 28.83 nm, for MgO-CuO( CuO

10%) nanocomposites calcined at 600 0C for 4hrs is 29.74 nm and for MgO-CuO( CuO

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15%) nanocomposites calcined at 600 0C for 4hrs is 34.24 nm because Cu atom is more

atomic radius then Mg atom resulting the increase of crystallite size with increase of

concentration of CuO in samples of MgO-CuO nanocomposites. The calculated values of

crystallite size are presented in Table 4.1.


FTIR Spectra of the MgO-CuO (5%,10%,15%) nanocomposites calcined at 6000C

for 4 hrs and 6 hrs of prepared sample are shown in Figures 4.12 and 4.13 respectively.

Perusal of the figure 4.13 shows the IR peaks at around 3426 cm-1 ,1636 cm-1 ,1459 cm-1,

1023 cm-1, 862 cm-1 and 652 cm-1 and these peaks are at same position exhibited as in IR

spectra of MgO nanoparticles(as discussed in Chapter-3). An additional peak is observed

at 535 cm-1 in Figure 4.12(A) and for seen their variation the magnified image is

reproduced in Figure 4.12(B). The absorption peak at 535 cm-1 was mainly attributed to

the presence of CuO stretching vibration in the nanomaterials [29]. Peaks occurring in the

range 400-1000 cm-1 in FTIR spectrum confirmed the presence and purity of MgO-CuO

(5%,10%,15%) nanocomposites.

(A) (B)Figure 4.12(A) FTIR Spectroscopy of MgO-CuO nanocomposites with different

cocentrations calcined at 600 0C for 4 hrs(a) MgO-CuO(5%) nanocomposites (b)MgO-CuO(15%) nanocomposites at 600 0C for 4 hrs (c) MgO-CuO(15%)

nanocomposites (B) same as (A)but magnified view with different scale

FTIR Spectra of the MgO-CuO (10%) nanocomposite calcined at 6000C for 4 hrs and

6 hrs of prepared sample are shown in Figure 4.13. Persual of the figure shows that

transmittance of the all calcined samples decreases with increase in the duration of

96

calcination temperatures (from 4 hrs to 6 hrs), It might be due to phase transformation of

CuO at higher temperature or more calcined duration.

Figure 4.13 FTIR Spectroscopy of MgO-CuO (10%) nanocomposites calcined at600 0C for (a) 4 hrs (b) 6 hrs

4.4.2.3 UV-VIS Spectral Studies

UV-VIS spectra of all the samples were recorded in the wavelength range 200 to 800

nm and for the UV–Visible absorption measurement, the calcined MgO-CuO

nanocomposites samples are ultrasonically dispersed in absolute ethanol. The recorded

graph in absorption spectra is absorbance versus wavelength for MgO-CuO (10%)

nanocomposite calcined at fixed temperature (600 0C) for different duration of time are

shown in Figure 4.14.The absorption graph of MgO nanoparticles is reproduced from

Chapter-3 for comparison purpose. It has been found that firstly the absorbance decreases

with an increase in wavelength, and a sharp decrease in absorbance near the band edge

(200 nm) indicating the nanostructure nature of the samples [30] thereafter the value of

absorption coefficient are decreases continuously and it has been found that absorption of

MgO-CuO (10%) nanocomposites is higher than MgO nanoparticles at same calcined

temperature and same duration of calcination and also the nanocomposites particles are

less uniform size than MgO nanoparticles. The value of absorption co-efficient is

increases as the duration of calcination increases for fixed calcination temperature and the

similar patterns were seen in other concentration MgO-CuO nanocomposites for similar

conditions as shown in Figure 4.15.

97

Figure 4.14 Absorption graph of (a) MgO nanoparticles calcined at 600 0C for 4 hrs(b) MgO-CuO(10%) nanocomposites calcined at 600 0C for 4 hrs (c) MgO-CuO(10%)

nanocomposites calcined at 600 0C for 6 hrs

The effect of variation of CuO concentration in absorption spectra were examined in

MgO-CuO (CuO 5%, 15%) nanocomposites for different durations of calcination and at

fixed calcination temperature , which are shown in Figure 4.15. Perusal of the figure

shows that absorption value decreases with increase of concentration because composition

of CuO ( i.e. CuO + Cu2O) is changed at higher temperature such as 600 0C [31].

Figure 4.15 Absorption graph of MgO-CuO nanocomposites with differentconcentrations calcined at 600 0C for different durations (a) MgO-CuO(5%)

nanocomposites for 4hrs (b) MgO-CuO(5%) nanocomposites for 6 hrs (c) MgO-CuO(15%) nanocomposites for 4 hrs (d) MgO-CuO(15%) nanocomposites for 6 hrs .

98

Tauc plots were used to determine the optical energy band gap of calcined

nanocomposites samples as shown in Figures 4.16 and 4.17 and the band gap energy of

MgO-CuO (CuO 5,10%, 15%) nanocomposites are estimated by using the transition rate

equation for direct transition of semiconductor. The absorption coefficient for direct

transition is given by the equation (as discussed in Chapter-3):

α(hv) = A(hv- Eg)n

where hv= photon energy, α= absorption coefficient with α=4πk/λ; k is the absorption

index or absorbance, λ is the wavelength in nm, Eg is the band gap energy. A= constant.

For the present work, n= ½ corresponding to the allowed direct transition was found to

hold and the corresponding Tauc plot are shown in Figures 4.16 and 4.17 respectively.

Figure 4.16 Tauc plots of MgO-CuO(10%) nanocomposites at 600 0C for(a) 4 hrs(b) 6 hrs


tabulated in Table 4.4 and it was found that all the transition were direct allowed transition

and value of energy band gap decrease as the duration of calcination increases. It might be

due to quantum confinement effect i.e. increase of the crystallite size, decrease the band

gap energy, because the crystal lattice expands and the interatomic bonds are weakened.

Weaker bonds means less energy is needed to break a bond and get an electron in the

conduction band [32].

The Tauc plot of MgO-CuO(10%) nanocomposites for different concentration for

fixed duration of calcination at fixed temperature (600 0C) is shown in Figures 4.7(A) and

Perusal of Figure 4.7(A). Perusal of Figure shows that values of band gap energy more or

99

less constant (slightly increases) with increase of dopant concentration. The values of

band gap of calcined samples calculated from Tauc plot is tabulated in Table 4.2.

Figure 4.17 Tauc plot of MgO-CuO nanocomposites with different concentrationscalcined at 600 0C for different durations 4 hrs (a) MgO-CuO(5%) nanocomposites

for 4 hrs (b) MgO-CuO(5%) nanocomposites for 6 hrs (c) MgO-CuO(15%)nanocomposites for 4 hrs (d) MgO-CuO(15%) nanocomposites for 6 hrs .

Table 4.4 Optical Band Gap of MgO nanoparticles and MgO-CuO nanocomposites


Sr.No.

Name of sample Time duration forcalcination

Optical energyband ( in eV)

1 MgO nanoparticles 4 hrs 4.62 MgO nanoparticles 6 hrs 4.13 MgO-CuO(5%) nanocomposites 4 hrs 3.93 MgO-CuO(5%) nanocomposites 6 hrs 3.83 MgO-CuO(10%) nanocomposites 4 hrs 4.04 MgO-CuO(10%) nanocomposites 6 hrs 3.455 MgO-CuO(15%) nanocomposites 4 hrs 4.046 MgO-CuO(15%) nanocomposites 6 hrs 3.98


TEM images of MgO-CuO nanocomposites calcined at 600 0C for 4 hrs and for

different concentration are shown in Figures 4.18(a) and 4.18(b) respectively. Perusal of

the figure shows the size of the particles of MgO-CuO(10%) calcined for 4hrs are lie in

the range 28.01nm to 32.25nm and average crystallite size comes out to be 30 nm. The

TEM results are in accordance with those of XRD results and observed that crystallite size

increases with dopant concentration. From images it was observed spherical in shape.

100

(A) (B)Figure 4.18 TEM images of samples calcined at 600 0C for 4 hrs (A) MgO-CuO( CuO

10%) nanocomposites (B) MgO-CuO( CuO 15%) nanocomposites

4.4.2.5 Scanning Electron Microscopy (SEM) studies

The SEM images of MgO-CuO nanocomposites calcined at 600 0C for 4 hrs and 6 hrs


typical SEM image of MgO-CuO nanocomposites calcined at 600 0C for 4 hrs is shown in

Figure 4.19 ,perusal image show that particles are uniform in size, agglomerated in nature

and truncated spherical in shape.

Figure 4.19 SEM image of MgO-CuO (10%) nanocomposites at 600 0C for 4 hrs

4.4.2.6 CONCLUSIONS

1. MgO-CuO nanocomposites of different concentration for have been prepared by

using Co-precipitation method. The crystallite size of calcined nanocomposites samples of

100










4.4.2.6 CONCLUSIONS



100










4.4.2.6 CONCLUSIONS



101

different dopant concentration were estimated by using Debye-Scherer formula and

tabulated in Table-4.3 and observed that the average crystallite sizes ware increases with

increases the duration of calcination at fixed calcination temperature; it might be due to

increases the growth of crystals as the duration of calcination increases at fixed calcination

temperature.

2. Crystallite size of nanocomposites increases with increase of concentration of CuO

in the samples for fixed duration of calcination and at fixed calcination temperature

because Cu atom having more atomic radius than MgO atom.

3. Perusal of FTIR Spectra of calcined sample of MgO-CuO (5%, 10%, 15%)

nanocomposites shows near about at 3426 cm-1 , 1636cm-1, 1459 cm-1,1023 cm-1 ,862

cm-1and 652 cm-1 are same as appeared in MgO nanoparticles(as discussed in Chapter-3)

and an additional peak is found at 535 cm-1 were due to presence of CuO in the sample

i.e. M-O-M vibration of CuO particles. So FTIR spectra confirm the synthesis and purity

of MgO-CuO nanocomposites.

4. The transmittance of calcined samples decreases with increase of the duration of

calcination (4 hrs to 6 hrs) for fixed calcination temperature. It might be due to the

different phase formation of copper oxide (i.e. CuO, Cu2O ) at higher temperature such as

600 0C.

5. The energy band gap of calcined samples were determined by Tauc plot and it has

been found that all the energy bands are direct allowed energy transition and observed

value of energy band gap is more or less constant or slightly increase with increasing the

dopant concentration and decrease with increases the duration of calcination, it might be

due to quantum confinement effect.

6. From absorption spectra, It has been found that the absorbance decreases with an

increase in wavelength, and a sharp decrease in absorbance near the band edge (200 nm )

indicating the crystalline nature of the samples and particles are uniform in shape and

absorption increases with increases the time duration of calcination for fixed temperature.

7. From absorption spectra, it has been found that the absorbance decreases with

increase of CuO dopant concentration in the sample for fixed duration of time at fixed


8. Perusal of TEM images of MgO-CuO nanocomposites shows that all the calcined

MgO-CuO nanocomposites were lie in the range of 28.01 nm to 32.25nm and average

particle size is 30nm and are in accordance with XRD results. From TEM images it has

been observed that particles are spherical in shape.

102

9. Perusal of SEM image of MgO-CuO nanocomposites shows that particles are

uniform and agglomerated in nature and spherical in shape.

4.4.3 Characterization of MgO-Fe2O3 nanocomposites

4.4.3.1 X-ray diffraction (XRD) Studies



range of 100–800. The XRD patterns of MgO-Fe2O3 nanocomposites calcined for different

duration of time (4 hrs and 6 hrs) at fixed temperature (600 0C) were shown in Figure

4.20 and XRD pattern of MgO nanoparticles calcined at 600 0C for 4hrs are reproduce

from Chapter-3 for comparison purpose.

Figure 4.20 XRD patterns of (a) MgO nanoparticles calcined at 6000C for 4 hrs (b)MgO-Fe2O3 (10%) nanocomposites calcined at 6000C for 4 hrs


described in Chapter-3). The major peaks for γ-Fe2O3 nanoparticles are reported to be at

2θ~24.300, 35.660, 43.170, 57.170 and at 78.820 as per the JCPDS card no. 86-0550. The

peaks at 38.50 , 43.110,62.450 and 78.00 appear to be merged in the peaks of MgO

corresponding to position at 37.140, 43.110, 62.720 for nanocomposites. The development

103

of addition peaks at 2θ~ 23.700, 35.650, and 57.100 in nanocomposites are due to the

presence of γ-Fe2O3 in nanocomposites.

Crystallite size of nanocomposites were determined by using Debye-Scherrer’s

equation ( as discussed in chapter-3)

D = 0.9 λ / β cosθ

where D is the crystallite size, λ is the wavelength of X-ray beam, β is the full width at

half maximum of the most intense peak, and 2θ is the Bragg diffraction angle of the


Table 4.5 XRD data of MgO nanoparticles and MgO-Fe2O3 nanocomposites calcined at

6000C for different duration


Positionof mostintensePeak

Value ofFWHM formost intensePeak(β)

crystallitesize

1 MgO NPs 4 hrs 43.1164 0.4117 18.97 nm

2 MgO-Fe2O3 (5%) NCs 4 hrs 43.111 0.3314 25.47 nm

3 MgO-Fe2O3 (10%) NCs 4 hrs 43.055 0.3149 26.85 nm

4 MgO-Fe2O3 (10%) NCs 6 hrs 43.064 0.2238 37.9 nm

5 MgO-Fe2O3 (15%) NCs 4 hrs 43.116 0.2312 36.41 nm

The effect of variation of concentration of Fe2O3 in MgO-Fe2O3 nanocomposites for

fixed time duration of calcinations and for fixed calcination temperature at 600 0C for

4hrs of XRD patterns is shown in Figure 4.11.

104

Figure 4.21 XRD patterns of MgO-Fe2O3 nanocomposites with differentconcentrations calcined at 6000C for 4 hrs(a) MgO-Fe2O3 (5%) nanocomposites (b)MgO-Fe2O3 (15%) nanocomposites

Perusal of XRD patterns shown in Figure 4.21 shows that peak of MgO and Fe2O3

nanomaterials are nearly in same position as appeared in previous case and only change in

intensity of peak observed and the crystallite size of MgO-Fe2O3 nanocomposites increases

with the increase of concentration of Fe2O3 composition in the sample i.e. MgO-Fe2O3

(Fe2O3 5%) nanocomposites calcined at 600 0C for 4hrs is 25.47 nm, for MgO-Fe2O3

(Fe2O3 10%) nanocomposites calcined at 600 0C for 4hrs is 26.85 nm and for MgO-Fe2O3

(Fe2O3 15%) nanocomposites calcined at 600 0C for 4hrs is 37.9 nm because Fe atom is

more atomic radius then Mg atom resulting the increase of crystallite size with increase of

concentration of Fe2O3 in samples of MgO-Fe2O3 nanocomposites. The calculated values

of crystallite size are presented in Table 4.5.


FTIR Spectra of the MgO- Fe2O3 (5%, 15%) nanocomposites calcined at 6000C for 4

hrs and 6 hrs of prepared sample are shown in Figures 4.22 and 4.23 respectively. Perusal

of the Figure 4.23 shows the IR band at around 3426 cm-1 , 2364 cm-1, 1442 cm-1 1022

cm-1, 862 cm-1 and these peaks are at same position exhibited as in IR spectra of MgO

nanoparticles (as discussed in Chapter-3). Two additional peaks are observed in at 574

cm-1 and 432 cm-1 in Figure 4.22(A) and for seen their variation the magnified image is

reproduced in Figure 4.22(B). The absorption peak at 574 cm-1 was mainly attributed to

the presence of γ-Fe2O3 stretching vibration in the sample [29]. At higher dopant

concentration an additional peak at 432 cm-1 is appears it might be due to vibration of γ-

105

Fe2O3 [34].Peaks occurring in the range 400-1000 cm-1 in FTIR spectra confirmed the

presence Fe2O3 and purity of MgO-Fe2O3 (5%,15%) nanocomposites.

(A) (B)Figure 4.22 (A) FTIR Spectra of MgO-Fe2O3 nanocomposites with different

concentrations calcined at 600 0C for 4 hrs (a) MgO-Fe2O3 (5%) nanocomposites (b)MgO-Fe2O3 (15%) nanocomposites (B) same as (A), but magnified view with

different scaleFTIR Spectra of the MgO-Fe2O3 (10%) nanocomposites calcined at 6000C for 4 hrs

and 6 hrs of prepared sample are shown in Figure 4.23. Perusal of figure shows that


calcination (from 4 hrs to 6 hrs) for fixed calcination temperature (600 0C), It might be due

to the increase of the condensation of the oxygen during calcination process. An addition

peak at 432 cm-1 is observed for higher calcination duration shows the presence of γ-Fe2O3

in the sample [35]..

Figure 4.23 FTIR Spectra of MgO-Fe2O3 (10%) nanocomposites calcined at 6000Cfor(a) 4 hrs (b) 6 hrs

106


UV-VIS spectra of all the samples were recorded in the wavelength range 200 nm to

800 nm and for the UV–Visible absorption measurement, the calcined MgO-Fe2O3


graph in absorption spectra is absorbance versus wavelength for MgO-Fe2O3 (10%)

nanocomposite calcined at fixed temperature (600 0C) for different duration of time are

shown in Figure 4.24 and it has been observed that firstly the absorbance decreases

sharply with an increase in wavelength near the band edge (270 nm) indicating the

nanostructure nature of the samples [36] thereafter the value of absorption coefficient are

more or less constant indicating the uniform particle size of sample The value of

absorption co-efficient is increases as the duration of calcination increases for fixed

calcination temperature as shown in Figure 4.24.

Figure 4.24 Absorption graph of MgO-Fe2O3 (10%) nanocomposites calcined at 6000C for(a) 4 hrs (b) 6 hrs

The effect of variation of Fe2O3 concentration in absorption spectra have been

examined in MgO-Fe2O3 (Fe2O3 5%, 15%) nanocomposites for fixed duration of

calcination and at fixed calcination temperature and are shown in Figure 4.25. Perusal of

the figure shows that absorption value increases with increase of concentration because

crystallite size increases with dopant concentration and rate of absorption is depanding on

the crystallite size of sample[37].

107

Figure 4.25 Absorption graph of MgO-Fe2O3 nanocomposites with differentconcentrations calcined at 600 0C for 4 hrs (a) MgO-Fe2O3 (5%) nanocomposites (b)MgO-Fe2O3 (15%) nanocomposites

The band gap energy of MgO-Fe2O3 (Fe2O3 5,10%, 15%) nanocomposites are

determined by using the transition rate equation for direct band gap semiconductor. The

absorption coefficient for direct transition is given by the equation (as discussed in

Chapter-3):

α(hv) = A(hv- Eg)n

where hv= photon energy, α= absorption coefficient with α=4πk/λ; k is the absorption


For the present work, n= ½ corresponding to the allowed direct transition was formed to


Figure 4.26 Tauc plots of MgO-Fe2O3 (10%) nanocomposites calcined at 600 0Cfor(a) 4 hrs (b) 6 hrs

108


tabulated in Table 4.6. From Tauc plot it was found that all the transition were direct





an electron in the conduction band [38].

The Tauc plot of MgO- Fe2O3 nanocomposites for different concentration for fixed

duration of calcination at fixed temperature (600 0C) is shown in Figure 4.26 and Perusal

of Figure 4.27 shows that values of optical band increases with increase of dopant

concentration. The values of band gap energy of nanocomposites are smaller than optical

band gap MgO nanoparticles. The values of band gap of calcined samples calculated from

Tauc plot is tabulated in Table 4.6 and values of MgO nanoparticles are reproduce in

table for comparison purpose.

Figure 4.27 Tauc plots of MgO-Fe2O3 nanocomposites with differentconcentrations calcined at 600 0C for 4 hrs(a) MgO-Fe2O3 (5%) nanocomposites (b)

MgO-Fe2O3 (15%) nanocomposites

109

Table 4.6 Optical Band Gap of MgO nanoparticles and MgO-Fe2O3 nanocomposites


Sr.No.

Name of sample Duration ofcalcination

Optical energyband ( in eV)

1 MgO nanoparticles 4 hrs 4.62 MgO nanoparticles 6 hrs 4.13 MgO-Fe2O3 (5%) nanocomposites 4 hrs 2.94 MgO- Fe2O3 (10%) nanocomposites 4 hrs 3.55 MgO- Fe2O3 (10%) nanocomposites 6 hrs 2.16 MgO- Fe2O3 (15%) nanocomposites 4 hrs 3.8


TEM images of MgO-Fe2O3 nanocomposites calcined at 600 0C for 4 hrs and for


the figure shows the size of the nanoparticles from 17.30 nm to 41.58 nm and average

crystallite size comes out from these results is 28 nm. The TEM results are in accordance

with those of XRD results and verified that crystallite size increases with dopant

concentration. From images it was observed that spherical in shape.

(A) (B)Fig 4.28 TEM images of MgO-Fe2O3 nanocomposites calcined at 600 0C for 4 hrs (A)

for Fe2O3 concentration (10%)(B) for Fe2O3 concentration (15%)


The SEM images of MgO-Fe2O3 nanocomposite calcined at 600 0C for 4hrs and 6 hrs


typical SEM image of MgO-Fe2O3 nanocomposites calcined at 600 0C for 4 hrs is shown

110

in Figure 4.29. Perusal of figure shows that particles are polycrystalline and agglomerated

in nature and truncated spherical in shape.

Fig 4.29 SEM image of MgO-Fe2O3 nanocomposites calcined at 600 0C for 4 hrs

4.4.3.6 CONCLUSIONS.

1. MgO-Fe2O3 nanocomposites of different concentration for have been prepared by

Co-precipitation method. The crystallite size of calcined nanocomposites samples of

different dopant concentration were evaluated by using Debye-Scherer formula and it has

been found that average crystallite size was increases with increases the duration of

calcination at fixed calcination temperature; it might be due to increases the growth of

crystals as the duration of calcination increases at fixed calcination temperature.

2. The crystallite size of nanocomposites increases with increase of concentration of

Fe2O3 in the samples for fixed duration of calcination and at fixed calcination temperature

because Fe atom having more atomic radius than Mg atom.

3. Perusal of FTIR Spectra of calcined samples of MgO-Fe2O3 (5%, 10%, 15%)

nanocomposites shows that band at 3426 cm-1 , 2364cm-1, 1442 cm-1, 1022 cm-1 and 862

cm-1 are same as appeared in MgO nanoparticles which is discussed in Chapter-3 and two

additional peak are found at 574 cm-1 and 432 cm-1 were due to presence of Fe2O3 in the

sample i.e. Fe-O-Fe vibration of Fe2O3 particles. So FTIR spectra confirm the synthesis

and purity of MgO-Fe2O3 nanocomposites.

110




















110




















111


calcination (4 hrs to 6 hrs) for fixed calcination temperature (600 0C). It might be due to

the increase of the condensation of the oxygen during calcination process.

5. The optical energy band gap of calcined samples were determined by Tauc plot and

it has been found that all the energy bands are direct allowed energy bands and observed

value of energy band gap is increases with the increase of the dopant concentration and

decreases with increase of the duration of calcination, it might be due to quantum

confinement effect i.e. As crystallite size of sample increases, the value of energy band

gap decreases.

6. From absorption spectra, It has been found that the absorption decreases sharply

with an increase in wavelength near the band edge (270 nm) indicating the nanocrystalline

nature of the samples and particles are uniform in shape and absorption increases with

increases the time duration of calcination for fixed temperature.

7. From absorption spectra, It has been found that the absorbance decreases with

increase of Fe2O3 dopant concentration in the sample for fixed duration of time at fixed


8. Perusal of TEM images of MgO-Fe2O3 nanocomposites shows that all the calcined

MgO-Fe2O3 nanocomposites were in the range of 17 nm to 41 nm and average particles

sizes is 28 nm ,which is in accordance with XRD results. From TEM images it has been

observed that particles are spherical in shape and agglomerated in nature.

9. Perusal of SEM image of MgO-Fe2O3 nanocomposites shows that particles are

uniform and agglomerated in nature and spherical in shape.

4.4.4 Characterization of MgO-Co3O4 nanocomposites4.4.4.1 X-ray diffraction (XRD) Studies



range of 100–800.The XRD patterns of MgO- Co3O4 nanocomposites calcined for different

duration of time (4 hrs and 6 hrs) at fixed temperature (600 0C) were shown in Figure

4.30 and XRD pattern of MgO nanoparticles calcined at 600 0C for 4hrs are reproduce

from Chapter-3 for comparison purpose.

112

Figure 4.30(a) XRD patterns of MgO nanoparticles calcined at 6000C for 4 hrs andMgO-Co3O4 (10%) nanocomposites calcined at 6000C for(b) 4 hrs (c) 6 hrs


described in Chapter-3). The major peaks for Co3O4 nanoparticles are reported to be at

2θ~34.7680, , 44.7630, 47.5690 , 62.72850and at 74.050 as per the JCPDS card no. 074-

2120. The peaks at 38.80 , 44.70 and 78.00 appear to be merged in the peaks of MgO

corresponding to position at 38.820, 42.970, 62.330 ,74.100 and 78.050 for nanocomposites.

The development of addition peaks at 2θ~ 35.780 and 47.560 in nanocomposites is due to

the presence of Co3O4 in nanocomposites .

Crystallite size of powder samples and were calculated by using Debye-Scherrer’s

equation(as discussed in chapter-3)

D = 0.9 λ / β cosθ

where D is the crystallite size, λ is the wavelength of X-ray beam, β is the full width at

half maximum of the most intense peak, and 2θ is the Bragg diffraction angle of the


113

Table 4.7 XRD data of MgO nanoparticles and MgO-Co3O4 nanocomposites calcined

at 6000C for different duration of time.


Positionof mostintensePeak(indegrees)

Value ofFWHM(β) (inradians)

Crystallitesize(D)

1 MgO NPs 4 hrs 43.1164 0.4117 18.97 nm2 MgO NPs 6 hrs 43.0396 0.4007 21.07 nm3 MgO- Co3O4 (5%) NCs 4 hrs 43.085 0.2419 34.90 nm4 MgO- Co3O4 (5%) NCs 6 hrs 43.097 0.2855 29.53nm5 MgO- Co3O4 (10%) NCs 4 hrs 43.074 0.2762 30.57 nm6 MgO- Co3O4 (10%) NCs 6 hrs 43.056 0.3058 27.60 nm7 MgO- Co3O4 (15%) NCs 4 hrs 43.068 0.3213 26.28 nm8 MgO- Co3O4 (15%) NCs 6 hrs 43.024 0.3519 23.99 nm

Perusal of XRD patterns shown in Figure 4.30 show that peak of MgO and Co3O4


nanomaterials [39] and additional peaks were observed at position 2θ ~ 35.780

,36.980,38.820 which is corresponding to Co3O4 peak confirm from JCPDS data for MgO

JCPDS card no.78-0430 and for Co3O4 JCPDS card no. 074-2120 .The crystallite size of

MgO-Co3O4 nanocomposites decreases with time duration of calcination i.e. MgO-Co3O4

(10%) nanocomposites calcined at 600 0C for 4hrs is 35.57 nm and for 6 hrs is 27.60 nm

and for confirmation of results i.e. the decrease of crystallite size with duration of

calcination, the characterization process is carried out for other concentration samples and

similar results were obtained in other samples and are shown in Table 4.7.It might be due

to the different phase formation in cobalt oxide i.e. CoO, Co2O3, Co3O4. The crystallite

size also increases from MgO nanoparticles calcined at 600 0C for 4hrs i.e. 18.97 nm to

MgO-Co3O4(10%) nanocomposites 600 0C for 4hrs i.e. 30.57 nm and similar results were

obtained for other nanocomposites samples calcined for different duration of time for fixed

calcination temperature, because Co atom is more atomic radii then Mg atom resulting

increase of crystallite size of MgO-Co3O4 nanocomposites [40].

The effect of variation of concentration of Co3O4 in MgO-Co3O4 nanocomposites for

fixed time duration of calcinations and for fixed temperature at 600 0C of XRD patterns is

shown in Figure 4.11.

114

Figure 4.31 XRD patterns of MgO-Co3O4 nanocomposites for variousconcentrations calcined at 6000C for different calcination durations(a) MgO-Co3O4

(5%) nanocomposites for 4 hrs (b) MgO-Co3O4 (5%) nanocomposites for 6 hrs (c)MgO-Co3O4 (15%) nanocomposites for 4 hrs (d) MgO-Co3O4 (15%) nanocomposites

for 6 hrs.

Perusal of XRD patterns shown in Figure 4.31 shows that peak of MgO and Co3O4


nanomaterials[41] and the crystallite size of MgO-Co3O4 nanocomposites decreases with

increase of Co3O4 composition in the sample i.e. MgO-Co3O4 (Co3O4 5%)

nanocomposites calcined at 600 0C for 4hrs is 34.90 nm, for MgO-Co3O4 (Co3O4 10%)

nanocomposites calcined at 600 0C for 4hrs is 30.57 nm and for MgO- Co3O4 (Co3O4 15%)

nanocomposites calcined at 600 0C for 4hrs is 26.28 nm because different phase formation

in cobalt oxide at high temperature such as 6000C i.e. CoO, Co2O3, Co3O4.. The calculated

values of crystallite size are presented in Table 4.7.


FTIR Spectra of the MgO-Co3O4 (Co3O4 5%,10%,15%) nanocomposites calcined at

6000C for 4 hrs and 6 hrs of prepared sample are shown in Figures 4.32 and 4.33

respectively. Perusal of the figure shows IR band around at 3500 cm-1 ,2362 cm-1 ,1793

cm-1,1508 cm-1, 869 cm-1, and these peaks are at same position exhibited as in IR spectra

of MgO nanoparticles as discussed in Chapter-3. An additional peak is observed at 523

cm-1 in Figure 4.33. The absorption peak at 523 cm-1 was mainly attributed to the presence

of Co3O4 stretching vibration in the nanomaterials in the sample [41]. Peaks occurring in

115

the range 400-1000 cm-1 in FTIR spectrum confirmed the presence and purity of MgO-

Co3O4 (Co3O4 5%,10%,15%) nanocomposites.

Figure 4.32 FTIR Spectra of MgO-Co3O4 nanocomposites with differentconcentrations calcined at 600 0C for 4 hrs(a) MgO-Co3O4 (5%) nanocomposites (b)MgO-Co3O4 (10%) nanocomposites (c) MgO-Co3O4 (15%) nanocomposites

FTIR Spectra of the MgO- Co3O4 (10%) nanocomposite calcined at 6000C for 4 hrs

and 6 hrs of prepared sample are shown in Figure 4.33. Perusal of the figure shows that


calcination temperatures (from 4 hrs to 6 hrs), It might be due to phase transformation of

Co3O4 at higher temperature or more calcined duration.

Figure 4.33 FTIR Spectra of MgO-Co3O4 (10%) nanocomposites calcined at 600 0Cfor (a) 4 hrs (b) 6 hrs.

116


UV-VIS spectra of all the samples were recorded in the wavelength range 200 nm to

800 nm and for the UV–Visible absorption measurement, the calcined MgO-Co3O4


graph in absorption spectra is absorbance versus wavelength for MgO-Co3O4 (10%)

nanocomposites calcined at fixed temperature (600 0C) for different duration of time are

shown in Figure 4.34 and from obtained result, It has been found that firstly the

absorbance decreases sharply with increase in wavelength near the band edge (310 nm)

indicating the nanostructure nature of the samples [41] thereafter the value of absorption

coefficient are more or less constant which show that nanocomposites particles are

uniform in crystallite size. The value of absorption co-efficient is increases as the duration

of calcination increases for fixed calcination temperature and the similar patterns were

seen in other concentration MgO-Co3O4 nanocomposites for similar conditions as shown

in Figure 4.35.

Figure 4.34 Absorption graph of MgO-Co3O4 (10%) nanocomposites calcined at600 0C for(a) 4 hrs (b) 6 hrs

The effect of variation of Co3O4 concentration in absorption spectra have been

examined in MgO-Co3O4 (Co3O4 5%, 15%) nanocomposites for different duration of

calcination and at fixed calcination temperature and are shown in Figure 4.35. Perusal of

the figure shows that absorption value decreases with increase of concentration because

composition of Co3O4 increases in the MgO-Co3O4 nanocomposites. From XRD graph it

has been found that crystallite size of sample decreases with increase of dopant

concentration and absorption rate is a function of size of material i.e. absorption rate

increases as the size of sample increases which have similar results described in earlier

series.

117

Figure 4.35 Absorption graph of MgO-Co3O4 nanocomposites with differentconcentrations calcined at 600 0C for different durations of calcination (a) MgO-

Co3O4 (5%) nanocomposites for 4 hrs (b) MgO-Co3O4 (15%) nanocomposites for 4hrs (c) MgO-Co3O4 (15%) nanocomposites for 6 hrs .

The band gap energy of MgO-Co3O4 (Co3O4 5%,10%, 15%) nanocomposites are

estimated by using the transition rate equation for direct band gap semiconductor. The

absorption coefficient for direct transition is given by the equation as discussed in Chapter-

3r:

α(hv) = A(hv- Eg)n

where hv= photon energy, α= absorption coefficient withα=4πk/λ; k is the absorption


For the present work, n= ½ corresponding to the allowed direct transition was found to


Figure 4.36 Tauc plot of MgO-Co3O4 (10%) nanocomposites calcined at 600 0C for(a) 4 hrs (b) 6 hrs.


tabulated in Table 4.8. From Tauc plot it was found that all the transition were direct

118





an electron in the conduction band , which is described in detail in earlier series.

The Tauc plot of MgO- Co3O4 (10%) nanocomposites for different concentration for

fixed duration of calcination at fixed temperature (600 0C) is shown in Figure 4.7(A) and

Perusal of Figure 4.7(A). Perusal of Figure shows that values of band gap energy

decreases with increase of dopant concentration. It might be due to quantum confinement

effect. The values of band gap of calcined samples calculated from Tauc plot is tabulated

in Table 4.2.

Figure 4.37 Tauc plot of MgO-Co3O4 nanocomposites with different concentrationscalcined at 600 0C for different duration (a) MgO-Co3O4 (5%) for 4 hrs (b) MgO-

Co3O4 (15%) nanocomposites for 4 hrs (c) MgO-Co3O4 (15%) nanocomposites for 6hrs .

Table 4.8 Optical Band Gap of MgO nanoparticles and MgO-Co3O4 nanocomposites


Sr.No.

Name of sample Time duration ofcalcination

Band gapl energy( in eV)

1 MgO nanoparticles 4 hrs 4.62 MgO nanoparticles 6 hrs 4.13 MgO-Co3O4 (5%) nanocomposites 4 hrs 3.93 MgO-Co3O4 (10%) nanocomposites 4 hrs 3.994 MgO-Co3O4 (10%) nanocomposites 6 hrs 3.885 MgO-Co3O4 (15%) nanocomposites 4 hrs 4.26 MgO-Co3O4 (15%) nanocomposites 6 hrs 3.1

119


TEM images of MgO-Co3O4 nanocomposites calcined at 600 0C for 4 hrs and for


the figure shows the size of the nanoparticles for 15% are lie in the 10.43 nm to 25.73 nm

and average crystallite size comes out from these results is 18 nm. The TEM results are in

accordance with those of XRD results and verified that crystallite size decreases with

increase of dopant concentration. From images it was observed that particles are spherical

in shape.

(a) (b)Figure 4.38 TEM images of MgO-Co3O4 nanocomposites with variousconcentrations calcined at 600 0C for 4 hrs(a) MgO-Co3O4 (10%) nanocomposites (b)MgO-Co3O4 (15%) nanocomposites


The SEM images of MgO-Co3O4 nanocomposites calcined at 600 0C for 4hrs and 6

hrs were more or less similar to MgO nanoparticles, which is described in Chapter-3 and

typical SEM image of MgO-Co3O4 nanocomposites calcined at 600 0C for 4 hrs is shown

in Figure 4.19. Perusal of Figure 4.19, show that particles are uniform in size,

agglomerated in nature and truncated spherical in shape.

120

Figure 4.39 SEM image of MgO-Co3O4(10%) nanocomposites calcined at 600 0C for4 hrs

4.4.4.6 CONCLUSIONS

1. MgO-Co3O4 nanocomposites of different concentration for have been prepared by


different dopant concentration were estimated by using Debye-Scherer formula and it has

been found that average crystallite size was decreases with increases the duration of

calcination at fixed calcination temperature; it might be due to phase transformation of

cobalt oxide nanoparticles at higher temperature 600 0C.

2. The crystallite size of nanocomposites decreases with increase of concentration of

Co3O4 in the samples for fixed duration of calcination and at fixed calcination temperature

because Co atom having more atomic radius than MgO atom.

3. FTIR Spectra of MgO-Co3O4(5%, 10%, 15%) nanocomposites of calcined

sample were shown in Figures 4.12 & 4.13 and perusal of graph show that IR band

around at 3500 cm-1 ,2362 cm-1 ,1793 cm-1,1508 cm-1 and 869 cm-1, are same as

appeared in MgO nanoparticles which is discussed in Chapter third and an additional peak

is found at 523 cm-1 were due to presence of Co3O4 in the sample i.e. M-O-M vibration

of Co3O4 particles. So FTIR spectra confirm the presence of Co3O4 in MgO sample.


calcination (4 hrs to 6 hrs) for fixed calcination temperature. It might be due more

condensation of oxygen take place at large calcination duration so that the different phase

of cobalt oxide formation at higher temperature such as 600 0C.

120


4.4.4.6 CONCLUSIONS




















120


4.4.4.6 CONCLUSIONS




















121

5. The energy band gap energy of calcined samples were determined by Tauc plot and

tabulated in Table 4.8. From Tauc plot it has been found that all the energy bands are

direct allowed energy bands and observed value of energy band gap is decreases with

increase of the dopant concentration and decreases with the increase of the duration of

calcination, it might be due to quantum confinement effect i.e. As crystallite size of sample

increases, the value of energy band gap decreases.

6. From absorption spectra, It has been found that the absorbance decrease sharply

with an increase in wavelength near the band edge (310 nm) indicating the crystalline

nature of the samples and particles are uniform in shape and absorption increases with

increases the time duration of calcination for fixed temperature.

7. From absorption spectra, it has been found that the absorbance decreases with

increase of Co3O4 dopant concentration in the sample for fixed duration of time at fixed


8. Perusal of TEM images of MgO-Co3O4 shows that all the calcined MgO-Co3O4

nanocomposites were in the range of 10 nm to 25 nm and average particle size is 18 nm

,which is in accordance with XRD results. From TEM images it has been observed that

particles are spherical in shape and polycrystalline in nature.

9. Perusal of SEM image of MgO-Co3O4 shows that particles are polycrystalline in

nature and agglomerated in nature and spherical in shape.

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