CHAPTER 8 CONCLUSIONS AND SCOPE FOR FUTURE WORK

Transcription

1 CHAPTER 8 CONCLUSIONS AND SCOPE FOR FUTURE WORK In this thesis an experimental investigation about Magnisium oxide (MgO) nanoparticles and its nanocomposites i.e.mgo-x (X= NiO, CuO, Co3O4, Fe2O3, CeO2, Al2O3) with different concentration of dopant materials in 5%, 10%, 15% were carried out.the MgO nanoparticles samples have been synthesized by chemical-precipitation method and nanocomposites by Co-precipitation method.all the samples have been calcined at 6000C for duration 4 hrs and 6 hrs and then calcined samples have been characterized by using various characterization techniques such as XRD, UV-Visible spectroscopy, FTIR spectroscopy, TEM, SEM and in last the applications of MgO-Al2O3 nanocomposites i.e. fire-retardancy and UV-protection in textile also studied in respect of nanocomposites treated cotton fabrics and nanocomposites treated polyester-cotton blend fabrics. The brief description of thesis work given below. The main finding of the investigations of nanoparticles and various nanocomposites are summarized below: 8.1 Conclusions drawn from various series MgO nanoparticles 1. The crystallite size of synthesized nanoparticles calcined at 600 0C for 4 hour and 6 hour was estimated by using Debye-Scherrer formula and the average crystallite size was observed to increase with increase of the calcination temperature duration. 2. FTIR Spectra of the MgO nanoparticles calcined at 6000C for 4 hrs and 6 hrs show presence of the IR peak at around 3399 cm-1, 1467 cm-1,1058 cm-1, 864 cm-1 and 668 cm1. A broad band at which was attributed to stretching mode of -OH group, adsorption of CO2, different Mg-O-Mg vibration mode of MgO nanoparticles respectively. 3. The 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. 4. The energy band gap of the calcined samples was determined by Tauc plot and it was found that all the transition were direct allowed transition and the value of energy 177

2 band gap decreases as the duration of calcination increases. It might be due to quantum confinement effect i.e. increase the crystallite size, decrease the band gap. 5. From absorption spectra results, It has been found that firstly the absorbance decreases sharply with an increase in wavelength, near the band edge (367 nm) indicating the nanostructure of the samples [16] thereafter the value of absorption coefficient is more or less constant indicating the uniformity of size of synthesized particles. 6. TEM images indicating that all the synthesized samples were in the range of nanoscale and their sizes are in accordance with XRD results. The morphology of crystals is spherical in shape. 7. SEM image shows a general view of the morphology of calcined nanoparticles. It have been observed that all the synthesized nanomaterials were agglomerated in nature and spherical in shape MgO-NiO nanocomposites concentration were estimated 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. The 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. FTIR Spectra of calcined samples MgO-NiO (5%, 10%, 15%) nanocomposites show that peaks 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 178

3 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. The absorbance decreases with increase the NiO dopant concentration in the sample for fixed duration of time at fixed temperature of calcination. 8. 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 particles size comes to be 19 nm and in accordance with XRD results. From TEM images it has been observed that particles are spherical in shape and agglomerated in nature. 9. SEM image of calcined sample of MgO-NiO nanocomposites shows that particles are uniform and agglomerated in nature and spherical in shape MgO-CuO nanocomposites concentration were estimated by using Debye-Scherer formula and 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. FTIR Spectra of calcined sample of MgO-CuO (5%, 10%, 15%) nanocomposites shows that peaks at 3426 cm-1, 1636cm-1, 1459cm-1, 1023 cm-1, 862 cm-1 and 652 cm-1 are same as appeared in MgO nanoparticles which is 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. MO-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 179

4 different phase formation of copper oxide (i.e. CuO, Cu2O ) at higher temperature such as 600 0C. 5. All the energy bands are direct allowed 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. The absorbance decreases with increase of CuO dopant concentration in the sample for fixed duration of time at fixed temperature of calcination. 8. TEM images of MgO-CuO nanocomposites shows that all the calcined MgO-CuO nanocomposites were in the range of nm to nm and average particle size is 30nm,which is in accordance with XRD results. From TEM images it has been observed that particles are spherical in shape. 9. SEM image of MgO-CuO nanocomposites shows that particles are uniform and agglomerated in nature and spherical in shape MgO-Fe2O3 nanocomposites concentration were estimated 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. FTIR spectra of MgO-Fe2O3 (5%, 10%, 15%) nanocomposites shows that peaks 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 MgOFe2O3 nanocomposites. 180

5 4. The transmittance of calcined samples increases with increase of the duration of 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. All the energy bands are direct allowed transition and observed value of energy band gap is increase with increasing 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. The absorbance decreases with increase of Fe2O3 dopant concentration in the sample for fixed duration of time at fixed temperature of calcination. 8. TEM images of MgO-Fe2O3 nanocomposites shows that all the calcined MgOFe2O3 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. SEM image of MgO-Fe2O3 nanocomposites shows that particles are uniform and agglomerated in nature and spherical in shape MgO-Co3O4 nanocomposites concentration were estimated by using Debye-Scherer formula and the 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 show that broad band at 3498 cm-1, 2362cm-1, 1793 cm-1, 1508 cm-1 and 869 cm-1 are same as appeared in MgO nanoparticles which is discussed in Chapter-3 and an additional peak is found at 523 cm-1 were due to presence of Co3O4 in the sample i.e. 181

6 M-O-M vibration of Co3O4 particles. So FTIR spectra confirm the presence of Co3O4 in MgO sample. 4. The transmittance of calcined samples increases with increase of the duration of 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. 5. From Tauc plot it has been found that all the energy bands are direct allowed transitions and observed value of energy band gap is decrease with increasing the dopant concentration and decrease 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 decrease sharply with an increase in wavelength near the band edge (310 nm) indicating the crystallinity of the samples and particles are uniform in shape and absorption increases with increases the time duration of calcination for fixed temperature. 7. The absorbance decreases with increase of Co3O4 dopant concentration in the sample for fixed duration of time at fixed temperature of calcination. 8. TEM images of MgO-Co3O4 shows that all the calcined MgO-Co3O4 nanocomposites were in the range of 10 nm to 25 nm and the calculated average particle size is18 nm. The size results are in accordance with XRD results. From TEM images it has been observed that particles are spherical in shape and polycrystalline in nature. 9. SEM image of MgO-Co3O4 shows that particles are polycrystalline in nature and agglomerated in nature and spherical in shape MgO-CeO2 nanocomposites concentration were estimated by using Debye-Scherrer formula and the average crystallite sizes 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 CeO2 in the samples for fixed duration of calcination and at fixed calcination temperature because Ce atom having more atomic radius than MgO atom. 182

7 3. FTIR Spectra of MgO-CeO2 (5%, 10%, 15%) nanocomposites of calcined sample were show that peaks at 3398 cm-1, 1467cm-1, 1022 cm-1, 864 cm-1, 673 cm-1 are same as appeared in MgO nanoparticles which is discussed in Chapter-3 and an additional peaks are found at 533cm-1 and 434 cm-1 were due to presence of CeO2 in the sample i.e. CeO-Ce vibration of CeO2 particles. So FTIR spectra confirm the synthesis and purity of MgO-CeO2 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 as discussed in Chapter All the energy bands are direct allowed energy bands and observed value of energy band gap increases with increasing the dopant concentration and decreases with increasing 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 as discussed in Chapter From absorption spectra, It has been found that the absorbance decreases sharply with an increase in wavelength near the band edge (340 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. The absorbance decreases with increase of CeO2 dopant concentration in the sample for fixed duration of time at fixed temperature of calcination. 8. TEM images show that all the calcined MgO-CeO2 nanocomposites were in the range of 23 nm to 43 nm and average particles sizes are 34 nm and are in accordance with XRD results. From TEM images it has been observed that particles are spherical in shape and agglomerated in nature. 9. SEM image shows that particles are polycrystalline in formation and agglomerated in nature and spherical in shape MgO-Al2O3 nanocomposites concentration were estimated by using Debay-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. 183

8 2. The crystallite size of nanocomposites increases with increase of concentration of Al2O3 in the samples for fixed duration of calcination and at fixed calcination temperature because Al2O3 crystal contains 2Al and 3O atom so lattice size of nanocomposites crystal increases from MgO crystal. 3. FTIR Spectra of MgO- Al2O3 (5%, 10%, 15%) nanocomposites of calcined sample were studied and perusal of graph show that peaks at 3448 cm-1, 2364 cm-1, 1458 cm-1, 1092 cm-1, 848 cm-1, 662 cm-1 are same as appeared in MgO nanoparticles ( discussed in first series) and an additional peak is found at 528 cm-1 were due to presence of γ-al2o3 in the sample i.e. M-O-M(M-metal) vibration of γ-al2o3 particles. So FTIR spectra confirm the synthesis and purity of MgO-Al2O3 nanocomposites. 4. The transmittance of calcined samples decreases with increase of the duration of calcination ( 4 hrs to 6 hrs) for fixed calcination temperatures. It might be due to phase transformation Al2O3 (α-β-γ-al2o3)composition for higher calcination duration or may 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 plots 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 decrease 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 absorption decreases with an increase in wavelength, and a sharp decrease in absorbance near the band edge (200 nm to 320 nm) indicating the nano-crystalline nature of the samples and particles are uniform in shape and absorption increases drastically with increases the time duration of calcination for fixed temperature so that sample is used to treatment of the fabrics of application part in further study. 7. From absorption spectra, It has been found that the absorption increases with increase of Al2O3 dopant concentration in the sample for fixed duration of time at fixed temperature of calcination because crystallite size increases with dopant concentration. 8. TEM images shows that all the calcined MgO-Al2O3 nanocomposites were in the range of 15 nm to 21 nm and average particles sizes is 19 nm and these results are in accordance with XRD results. From TEM images it has been observed that particles are spherical in shape and agglomerated in nature. 184

9 9. SEM image shows that particles are uniform and agglomerated in nature and flower like shape Study of applications of MgO-Al2O3 nanocomposites in fabrics 1. The uniform distribution of the nanocomposites on the coated fabric is the prime objective for the functionality improvement. It is observed from the SEM images that the MgO-Al2O3 nanocomposites at different concentration levels in the coated fabrics are uniformly distributed on the surface of fabrics and also electrostatically bonded with the polymer structure. It is also noted that the agglomeration tendency of the nanoparticles on the coated fabric surface is minimal. Therefore, the concentration of nanoparticles can be further increased in the coated fabric beyond the applied levels. 2. The fire retardancy of the MgO-Al2O3 nanocomposites coated fabrics increases as the concentration of the nanocomposites increases in the coated fabric. The value of burning time for the coated samples is highest at 1.5 % o.w.f. MgO-Al2O3 nanocomposites in the coated fabrics. As the burning time increases significantly with the increasing concentration of nanocomposites, so a higher concentration beyond the trial levels of these nanoparticles could be possible. 3. The burning time of the MgO-Al2O3 nanocomposites coated fabrics at a concentration level of 1.5 % o.w.f. is equivalent to that of the Pyrovatex coated fabrics. The burning time for the MgO-Al2O3 nanocomposites coated cotton samples is higher than the PC blend fabrics. It is therefore, concluded that a higher concentration of MgO-Al2O3 nanocomposites is required for PC blend fabrics to achieve the same level of fire retardancy as that of the coated cotton fabrics. 4. The Limiting Oxygen Index (LOI) value of the MgO-Al2O3 nanocomposites coated cotton fabrics and Polyester Cotton blend fabrics increases as the concentration of the nanoparticles increases in the coated fabrics. The maximum value of LOI was observed for the coated fabrics having 1.5 % o.w.f. MgO-Al2O3 nanocomposites. The equivalent LOI values are observed for the coated cotton fabrics, PC blend fabrics with the MgO-Al2O3 nanocomposites and also with the Pyrovatex coated fabrics. 5. The ultraviolet protection rating of the MgO-Al2O3 nanocomposites coated fabrics increases as the concentration of the nanoparticles increases in the coated fabrics. The maximum value was observed for the coated fabrics having 1.5 % o.w.f. MgO-Al2O3 nanocomposites. The ultraviolet protection rating is higher for the MgO-Al2O3 nanocomposites coated PC blend fabrics than the coated cotton fabrics. It is, therefore, 185

10 concluded that a higher level of concentration of MgO-Al2O3 nanocomposites is required in the coated cotton fabrics to achieve the same level of ultraviolet protection rating as that of the PC blend fabrics. 8.2 Scope for Future Work The following suggestions are being made for future investigation of experimental work and possible extensions of this work: Nanocomposites compositions other than discussed above could be studied for structural and optical properties, eg., by changing the concentration of dopant materials such as concentration of CeO2 and Al2O3 may be apply more than 15% in MgO. In this thesis, optical and structural properties were studied at 6000C temperature in detail. It would be more interesting to study these properties at high temperature. Study of structural, electric and magnetic properties can also be done by substituting some other type of dopant to get nanocomposites samples with desired properties. In this thesis the applications of nanocomposites as fire retardant of MgO-Al2O3 treated fabrics have been studied in detail. It would be more interesting to study these properties of other synthesized nanocomposites Antibacterial properties of synthesized nanomaterials may be studied in future. Other structural properties like porosity may be studied in future. Magnetic properties and electrical could be may also be studied in order to get deeper in sight in the structure of nanocomposites. We can also make comparison between bulk samples with that of nanocrystalline samples. Dielectric properties like dielectric constant and Loss factor could be studied. We can also prepare thin film of these compositions for more effective device applications. 186