Chapter 4 SYNTHESIS AND CHARACTERIZATION OF MAGNISIUM OXIDETRANSITION METAL OXIDE NANOCOMPOSITES

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1 Chapter 4 SYNTHESIS AND CHARACTERIZATION OF MAGNISIUM OXIDETRANSITION 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 and 6 hrs and characterized by using various characterization techniques. The results are discussed in this Chapter Introduction Today 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 79

2 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 CeO 2, 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 (αfe2o3) 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 investigated Considering 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%). 80

3 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 Techniques Sample Synthesis Technique There are many synthesis techniques were described in Chapter-2 and the coprecipitation 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 2. 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 C 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 C and was,therefore, used for the present samples of nanocomposites. In order to see the effect of time duration, it has varied from to 6 hrs. 81

4 (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 deionized 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 deionized water and other condition of synthesis and calcination are same as discussed in synthesis of MgO-NiO nanocomposites 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 = Å). 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. 82

5 4.4 Results and Discussion Characterization of MgO-NiO nanocomposites 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 = Å) in the range of The typical XRD patterns of MgO-NiO(10%) nanocomposites calcined for different duration of time ( 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) (b) 6 hrs and MgO nanoparticles calcined at 6000C for (c) (d) 6 hrs XRD peaks of MgO appears at 2θ~ , , , , (as described in Chapter-3). The major peaks for NiO nanoparticles are reported to be at 2θ~ , and , as per the JCPDS card no The peaks at 38.50, , and appear to be merged in the peaks of MgO corresponding to 83

6 position at , , and 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 Calcination duration of time 1 MgO NPs 2 MgO NPs 3 Position of most intense Peak(in degrees) Crystallite size (D) Value of FWHM of most intense Peak (β)(in radian) hrs nm MgO-NiO (5%) NCs nm 4 MgO-NiO (10%) NCs nm 5 MgO-NiO (10%) NCs 6 hrs nm 6 MgO-NiO (15%) NCs nm nm The XRD patterns for MgO-NiO nanocomposites exhibit the XRD peaks both due to MgO and NiO as per the JCPDS card no for MgO and JCPDS card no 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 nm while for MgO-NiO nanocomposites containing 5%, 10%, 15% NiO the size becomes 21.77nm, 84

7 22.95 nm and 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) and MgO-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 nm for 4hrs calcination and 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 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 85

8 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 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 (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 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 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) (b) 6 hrs 86

9 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 0C for (a) (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]. 87

10 Figure 4.6 Absorption graph MgO-NiO nanocomposites with different concentrations and calcined at 600 0C for (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 (a) MgO-NiO(5%) nanocomposites (b) MgONiO(15%) nanocomposites (B) MgO-NiO(10%) nanocomposites calcined at 600 0C for (a) (b) 6 hrs 88

11 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. Name of sample No. Duration of calcination Energy band ( in ev) 1 MgO nanoparticles MgO nanoparticles 6 hrs MgO-NiO(5%) nanocomposites MgO-NiO(10%) nanocomposites MgO-NiO(10%) nanocomposites 6 hrs MgO-NiO(15%) nanocomposites > Transmission Electron Microscopy (TEM) studies TEM images of MgO-NiO nanocomposites calcined at 600 0C for 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. 89

12 (a) (b) Figure 4.8 TEM images of MgO-NiO nanocomposites with differen concentrations and calcined at 600 0C for (a) MgO-NiO (10%) nanocomposites (b) MgO-NiO (15%) nanocomposites 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 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 for 90

13 Conclusions 1. 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-OM vibration of NiO particles. So FTIR spectra confirm the synthesis and purity of MgONiO nanocomposites. 4. The transmittance of calcined samples increases with increase of the duration of calcination ( 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. 91

14 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 Characterization of MgO-CuO nanocomposites 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 = Å) in the range of 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 ( 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 (b) MgO-CuO(10%) nanocomposites calcined at 6000C for (c) MgO-CuO (10%) nanocomposites calcined at 6000C for 6 hrs 92

15 XRD peaks of MgO appears at 2θ~ , , , , (as described in Chapter-3). The major peaks for CuO nanoparticles are reported to be at 2θ~37.800, , , and at as per the JCPDS card no The peaks at 38.50, , and appear to be merged in the peaks of MgO corresponding to position at , , for nanocomposites. The development of addition peaks at 2θ~ , and in nanocomposites are due to the presence of CuO in nanocomposites samples. Crystallite size is estimated by using DebyeScherrer 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 maximum intense peak. The obtained values of β and D are presented in Table 4.3. 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 of calcination Position of most intense Peak hrs 6 hrs 6 hrs MgO NPs MgO- CuO (5%) NCs MgO-CuO (5%) NCs MgO-CuO (10%) NCs MgO-CuO (10%) NCs MgO-CuO (15%) NCs MgO-CuO (15%) NCs Value of FWHM of most intense peak (β) Crystallite size (D) nm nm nm nm nm nm 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~ , which is corresponding to CuO peak confirm from JCPDS card no for MgO and JCPDS card no 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 nm and for 6 hrs is nm.it might be due to the growth of crystal 93

16 improved and imperfection or defects in crystal decreases with increase the calcination time duration. The crystallite size also increases from MgO nanoparticles calcined at C for 4hrs i.e nm to MgO-CuO(10%) nanocomposites 600 0C for 4hrs i.e 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 Figure 4.11 XRD patterns of (a) MgO-CuO (5%) nanocomposites calcined at 6000C for (b) MgO-CuO (5%) nanocomposites calcined at 6000C for 6 hrs (c) MgOCuO (15%) nanocomposites calcined at 6000C for (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 MgOCuO nanocomposites increases with concentration of CuO composition i.e. MgO-CuO( CuO 5%) nanocomposites calcined at 600 0C for 4hrs is nm, for MgO-CuO( CuO 10%) nanocomposites calcined at 600 0C for 4hrs is nm and for MgO-CuO( CuO 94

17 15%) nanocomposites calcined at 600 0C for 4hrs is 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 Fourier Transform Infrared (FTIR) Studies FTIR Spectra of the MgO-CuO (5%,10%,15%) nanocomposites calcined at 6000C for 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 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 (a) MgO-CuO(5%) nanocomposites (b) MgO-CuO(15%) nanocomposites at 600 0C for (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 and 6 hrs of prepared sample are shown in Figure Persual of the figure shows that transmittance of the all calcined samples decreases with increase in the duration of 95

18 calcination temperatures (from 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 at 600 0C for (a) (b) 6 hrs 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

19 Figure 4.14 Absorption graph of (a) MgO nanoparticles calcined at 600 0C for (b) MgO-CuO(10%) nanocomposites calcined at 600 0C for (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 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 different concentrations calcined at 600 0C for different durations (a) MgO-CuO(5%) nanocomposites for 4hrs (b) MgO-CuO(5%) nanocomposites for 6 hrs (c) MgOCuO(15%) nanocomposites for (d) MgO-CuO(15%) nanocomposites for 6 hrs. 97

20 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) (b) 6 hrs The value band gap of the calcined samples was determined from Tauc plots are 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 98

21 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 concentrations calcined at 600 0C for different durations (a) MgO-CuO(5%) nanocomposites for (b) MgO-CuO(5%) nanocomposites for 6 hrs (c) MgO-CuO(15%) nanocomposites for (d) MgO-CuO(15%) nanocomposites for 6 hrs. Table 4.4 Optical Band Gap of MgO nanoparticles and MgO-CuO nanocomposites calcined at 600 0C for different duration of calcination Sr. Name of sample No. 1 2 MgO nanoparticles MgO nanoparticles 3 MgO-CuO(5%) nanocomposites MgO-CuO(5%) nanocomposites MgO-CuO(10%) nanocomposites MgO-CuO(10%) nanocomposites MgO-CuO(15%) nanocomposites 6 MgO-CuO(15%) nanocomposites Time duration for calcination 6 hrs 6 hrs 6 hrs 6 hrs Optical energy band ( in ev) Transmission Electron Microscopy (TEM) studies TEM images of MgO-CuO nanocomposites calcined at 600 0C for 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. 99

22 (A) (B) 0 Figure 4.18 TEM images of samples calcined at 600 C for (A) MgO-CuO( CuO 10%) nanocomposites (B) MgO-CuO( CuO 15%) nanocomposites Scanning Electron Microscopy (SEM) studies The SEM images of MgO-CuO nanocomposites calcined at 600 0C for and 6 hrs were more or less similar to MgO nanoparticles, which is described in Chapter-3 and typical SEM image of MgO-CuO nanocomposites calcined at 600 0C for 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 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

23 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 ( 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 temperature of calcination. 8. Perusal of TEM images of MgO-CuO nanocomposites shows that all the calcined MgO-CuO nanocomposites were lie in the range of 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. 101

24 9. Perusal of SEM image of MgO-CuO nanocomposites shows that particles are uniform and agglomerated in nature and spherical in shape Characterization of MgO-Fe2O3 nanocomposites 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 = Å) in the range of The XRD patterns of MgO-Fe2O3 nanocomposites calcined for different duration of time ( 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 (b) MgO-Fe2O3 (10%) nanocomposites calcined at 6000C for XRD peaks of MgO appears at 2θ~ , , , , (as described in Chapter-3). The major peaks for γ-fe2o3 nanoparticles are reported to be at 2θ~24.300, , , and at as per the JCPDS card no The peaks at 38.50, , and appear to be merged in the peaks of MgO corresponding to position at , , for nanocomposites. The development 102

25 of addition peaks at 2θ~ , , and 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 maximum intense peak. The obtained values of β and D are presented in Table 4.5. Table 4.5 XRD data of MgO nanoparticles and MgO-Fe2O3 nanocomposites calcined at 6000C for different duration Sr. No. Name of sample Duration of calcination Position of most intense Peak Value of FWHM for most intense Peak (β) crystallite size 1 MgO NPs nm 2 MgO-Fe2O3 (5%) NCs nm 3 MgO-Fe2O3 (10%) NCs nm 4 MgO-Fe2O3 (10%) NCs 6 hrs nm 5 MgO-Fe2O3 (15%) NCs 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

26 Figure 4.21 XRD patterns of MgO-Fe2O3 nanocomposites with different concentrations calcined at 6000C for (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 nm, for MgO-Fe2O3 (Fe2O3 10%) nanocomposites calcined at 600 0C for 4hrs is 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 Fourier Transform Infrared (FTIR) Studies 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 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 γ104

27 Fe2O3 [34].Peaks occurring in the range 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 (a) MgO-Fe2O3 (5%) nanocomposites (b) MgO-Fe2O3 (15%) nanocomposites (B) same as (A), but magnified view with different scale FTIR Spectra of the MgO-Fe2O3 (10%) nanocomposites calcined at 6000C for and 6 hrs of prepared sample are shown in Figure Perusal of figure shows that transmittance of the all calcined samples increases with increase in the duration of calcination (from 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 6000C for(a) (b) 6 hrs 105

28 UV-VIS Spectral Studies 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 nanocomposites samples are ultrasonically dispersed in absolute ethanol. The recorded 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 Figure 4.24 Absorption graph of MgO-Fe2O3 (10%) nanocomposites calcined at C for(a) (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 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]. 106

29 Figure 4.25 Absorption graph of MgO-Fe2O3 nanocomposites with different concentrations calcined at 600 0C for (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 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 4.26 and 4.27 respectively. Figure 4.26 Tauc plots of MgO-Fe2O3 (10%) nanocomposites calcined at 600 0C for(a) (b) 6 hrs 107

30 The value band gap of the calcined samples was determined from Tauc plots are tabulated in Table 4.6. From Tauc plot 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 [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 different concentrations calcined at 600 0C for (a) MgO-Fe2O3 (5%) nanocomposites MgO-Fe2O3 (15%) nanocomposites 108 (b)

31 Table 4.6 Optical Band Gap of MgO nanoparticles and MgO-Fe2O3 nanocomposites calcined at 600 0C for different duration of calcination Sr. No. Name of sample Duration of calcination Optical energy band ( in ev) 1 2 MgO nanoparticles MgO nanoparticles MgO-Fe2O3 (5%) nanocomposites MgO- Fe2O3 (10%) nanocomposites MgO- Fe2O3 (10%) nanocomposites MgO- Fe2O3 (15%) nanocomposites 6 hrs 6 hrs Transmission Electron Microscopy (TEM) studies TEM images of MgO-Fe2O3 nanocomposites calcined at 600 0C for and for different concentration are shown in Figures 4.28(a) and 4.28(b) respectively. Perusal of the figure shows the size of the nanoparticles from nm to 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 (A) for Fe2O3 concentration (10%)(B) for Fe2O3 concentration (15%) Scanning Electron Microscopy (SEM) studies The SEM images of MgO-Fe2O3 nanocomposite 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-Fe2O3 nanocomposites calcined at 600 0C for is shown 109

32 in Figure 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 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

33 4. The transmittance of calcined samples increases with increase of the duration of calcination ( 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 temperature of calcination. 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 Characterization of MgO-Co3O4 nanocomposites 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 = Å) in the range of The XRD patterns of MgO- Co3O4 nanocomposites calcined for different duration of time ( 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. 111

34 Figure 4.30(a) XRD patterns of MgO nanoparticles calcined at 6000C for and MgO-Co3O4 (10%) nanocomposites calcined at 6000C for(b) (c) 6 hrs XRD peaks of MgO appears at 2θ~ , , , , (as described in Chapter-3). The major peaks for Co3O4 nanoparticles are reported to be at 2θ~ ,, , , and at as per the JCPDS card no The peaks at 38.80, and appear to be merged in the peaks of MgO corresponding to position at , , , and for nanocomposites. The development of addition peaks at 2θ~ and 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 maximum intense peak. The obtained values of β and D are presented in Table

35 Table 4.7 XRD data of MgO nanoparticles and MgO-Co3O4 nanocomposites calcined at 6000C for different duration of time. Sr. No. Name of sample Duration of calcination hrs 6 hrs 6 hrs 6 hrs MgO NPs MgO NPs MgO- Co3O4 (5%) NCs MgO- Co3O4 (5%) NCs MgO- Co3O4 (10%) NCs MgO- Co3O4 (10%) NCs MgO- Co3O4 (15%) NCs MgO- Co3O4 (15%) NCs Position of most intense Peak(in degrees) Value of FWHM (β) (in radians) Crystallite size(d) nm nm nm 29.53nm nm nm nm nm Perusal of XRD patterns shown in Figure 4.30 show that peak of MgO and Co3O4 nanomaterials are nearly in same position which increase the intensity of peak of MgO nanomaterials [39] and additional peaks were observed at position 2θ ~ ,36.980, which is corresponding to Co3O4 peak confirm from JCPDS data for MgO JCPDS card no and for Co3O4 JCPDS card no 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 nm and for 6 hrs is 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 nm to MgO-Co3O4(10%) nanocomposites 600 0C for 4hrs i.e 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

36 Figure 4.31 XRD patterns of MgO-Co3O4 nanocomposites for various concentrations calcined at 6000C for different calcination durations(a) MgO-Co3O4 (5%) nanocomposites for (b) MgO-Co3O4 (5%) nanocomposites for 6 hrs (c) MgO-Co3O4 (15%) nanocomposites for (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 are nearly in same position which increase the intensity of peak of MgO 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%) 0 nanocomposites calcined at 600 C for 4hrs is nm, for MgO-Co3O4 (Co3O4 10%) nanocomposites calcined at 600 0C for 4hrs is nm and for MgO- Co3O4 (Co3O4 15%) nanocomposites calcined at 600 0C for 4hrs is 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 Fourier Transform Infrared (FTIR) Studies FTIR Spectra of the MgO-Co3O4 (Co3O4 5%,10%,15%) nanocomposites calcined at C for 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 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 114

37 the range cm-1 in FTIR spectrum confirmed the presence and purity of MgOCo3O4 (Co3O4 5%,10%,15%) nanocomposites. Figure 4.32 FTIR Spectra of MgO-Co3O4 nanocomposites with different concentrations calcined at 600 0C for (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 and 6 hrs of prepared sample are shown in Figure Perusal of the figure shows that transmittance of the all calcined samples increases with increase in the duration of calcination temperatures (from 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 0C for (a) (b) 6 hrs. 115

38 UV-VIS Spectral Studies 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 nanocomposites samples are ultrasonically dispersed in absolute ethanol. The recorded 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 Figure 4.34 Absorption graph of MgO-Co3O4 (10%) nanocomposites calcined at 600 0C for(a) (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 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. 116

39 Figure 4.35 Absorption graph of MgO-Co3O4 nanocomposites with different concentrations calcined at 600 0C for different durations of calcination (a) MgOCo3O4 (5%) nanocomposites for (b) MgO-Co3O4 (15%) nanocomposites for 4 hrs (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 Chapter3r: α(hv) = A(hv- Eg)n where hv= photon energy, α= absorption coefficient withα=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 4.36 and 4.37 respectively. Figure 4.36 Tauc plot of MgO-Co3O4 (10%) nanocomposites calcined at 600 0C for (a) (b) 6 hrs. The value band gap of the calcined samples was determined from Tauc plots are tabulated in Table 4.8. From Tauc plot it was found that all the transition were direct 117

40 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, 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 concentrations calcined at 600 0C for different duration (a) MgO-Co3O4 (5%) for (b) MgOCo3O4 (15%) nanocomposites for (c) MgO-Co3O4 (15%) nanocomposites for 6 hrs. Table 4.8 Optical Band Gap of MgO nanoparticles and MgO-Co3O4 nanocomposites calcined at 600 0C for different duration of calcination Sr. Name of sample No. 1 MgO nanoparticles 2 MgO nanoparticles MgO-Co3O4 (5%) nanocomposites MgO-Co3O4 (10%) nanocomposites MgO-Co3O4 (10%) nanocomposites 5 6 MgO-Co3O4 (15%) nanocomposites MgO-Co3O4 (15%) nanocomposites Time duration of calcination 6 hrs 6 hrs 6 hrs 118 Band gapl energy ( in ev)

41 Transmission Electron Microscopy (TEM) studies TEM images of MgO-Co3O4 nanocomposites calcined at 600 0C for and for different concentration are shown in Figures 4.38(a) and 4.38(b) respectively. Perusal of the figure shows the size of the nanoparticles for 15% are lie in the nm to 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 various concentrations calcined at 600 0C for (a) MgO-Co3O4 (10%) nanocomposites (b) MgO-Co3O4 (15%) nanocomposites Scanning Electron Microscopy (SEM) studies 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 is shown in Figure Perusal of Figure 4.19, show that particles are uniform in size, agglomerated in nature and truncated spherical in shape. 119