SYNTHESIS OF METAL OXIDES NANOSTRUCTURES FOR THE REMOVAL OF TOXIC RESIDUES

Abstract

From the last few decades, decontamination of chemical warfare agents (CWA) in the battlefield conditions and removal of heavy metal ions from the polluted water are the major challenges for the scientific community for the national security and human health interest. Among different CWA, sulphur mustard (HD) and sarin (GB) are well identified CWA and have been effectively employed in the World Wars (WW-I and WW-II) followed by its usage in several other incidents such as in Gulf War and in Japan by terrorist. HD affects several organs of the human including skin, mucous membrane which causes blisters. It also alkylates guanine nucleotide in DNA and causes fatality to the cells. GB attacks on nervous transmission and block it permanently by binding with the acetylcholinesterase enzyme, causing paralysis and mortality. On the other hand, presence of heavy metal ions such as lead, mercury, chromium, nickel, iron and other metals has a potentially harmful effect on human physiology and biological system. Hence, search for the technique and materials having high adsorption capacity to adsorb the CWA and removal of metal ions from water is essential. A number of adsorbent and techniques have been so far used to minimize the above problem and finally stops onto metal oxides nanostructures. Metal oxides structures synthesized at nanoscale demonstrate superior ability for the safety of human from CWA and heavy metal ions by mean of their remarkable capability including high adsorbing power and reactivity. These nanostructures can adsorb and degrade them through hydrolysis, elimination or oxidation reaction to convert them into non-toxics form. Also, heavy metal ions such as Cr (VI) and Pb (II) adsorb and removed from water by their preferential adsorption at highly reactive sites available in nanostructures. The reactivity and adsorption power of metal oxides nanostructures mainly because of their high surface area, large number of highly reactive edges, corner defect sites and unusual lattice planes. The main objective of the present work was to synthesize metal oxides based nanostructures including nanoparticles of copper oxide (CuO), tungsten oxide (WO3), zirconium oxide (ZrO2) and mixture of nanoparticles and nanorods of manganese oxide (MnO2) using reactive magnetron sputtering technique to investigate the decontamination ability for the degradation of CWA and removal of heavy metal ions from water. The effect of particle size on aforementioned issues was thoroughly investigated. The sputtering parameters were successfully controlled to analyse effect on structural, morphological and thermal properties of different metal vi oxides as well as to get the optimum particle size to minimize the above mentioned issues. A chapter wise summary of the thesis is given below. Chapter 1 gives an overview about the CWA, used by ambitious countries and terrorist to affect the environment and human life (in the first part) and another part gives about water related problem. The first part discusses the different type of CWA and their mechanism to affect the human health. Different type of decontaminant that was used to degrade these CWA was also discussed in this chapter. The mechanism of CWA degradation was also described using some important decontaminants such as bleaching powder, DS2 solution and some different metal oxides nanostructures and discussed their ability to degrade them. In the other part, discussion about the water pollutants was carried out, followed by different technologies and methods effective in minimizing the water related problem. Among them, absorption technology and adsorbents of different category are thoroughly discussed. After discussion of the problem and different treatments related to CWA and water pollution, we moves towards technology dependence over nanoscale materials that gives much better results towards decontamination of CWA and removal of heavy metal ions. Different synthesis techniques were discussed for preparation of the metal oxide nanostructures that were used in the CWA degradation and removal of heavy metal ions from water through adsorption technique. The usage of different nanostructures using adsorption technique were found effective solution of the above mentioned problems. Chapter 2 presents the details of synthesis and characterization techniques employed for the present work. Section 2.1 gives description about the nanoparticles formation. Section 2.2 discusses the process description and mechanistic details of DC reactive magnetron sputtering technique used for the preparation of nanostructures in the present work. Section 2.3 discusses the methodology used for the characterization of nanoparticles by different techniques such as XRay Diffraction (XRD) for the phase identification and grain size, Raman spectroscopy for the confirmation of structural phase. Field Emission Scanning Electron microscope (FESEM) and Transmission Electron Microscope (TEM) were used for the surface morphology analysis and electron diffraction scattering (EDS) for elemental composition analysis. N2BET analysis was used for surface area and pore size distribution, Thermogravimetric (TG) analysis for the water content onto the surface of nanoparticles. Gas Chromatograph equipped with Flame vii Ionization Detector (GCFID) was used for the kinetics measurement. Gas Chromatograph equipped with Mass Spectrometer (GCMS) and Fourier transform infrared spectroscopy (FTIR) were used for the characterization of the reaction products. Atomic adsorption spectroscopy (AAS) was used for the identification of elements concentration. Chapter 3 describes the synthesis and characterization of copper oxide nanoparticles at different sputtering parameters. Section 3.1 gives a brief introduction about the copper oxide nanoparticles followed by discussion on the work of different research groups contributed in the field of CWA degradation. Section 3.2 includes discussion on the temperature effect on the structural, morphological and thermal properties of the sputtered deposited copper oxide nanoparticles and their ability to degrade 2-chloro ethyl ethyl sulphide (CEES), well known simulant of sulphur mustard. The characterization of the nanoparticles was carried out by powder XRD, TEM, FESEM, N2BET, FTIR and TGA and the degradation kinetics was obtained by using GCFID. The reaction products was characterized by GCMS and then confirmed through FTIR technique. The average particle size of CuO nanoparticles calculated using XRD analysis was varied from 7 to 86 nm for asdeposited and annealing at different temperatures up to 900 °C. It was found that as the particle size increased as a function of annealing temperature and the rate of CEES degradation decreases from 0.434 to 0.134 h-1. The results indicates the role of hydrolysis reaction in the decontamination of CEES. The Section 3.3 discussed the structural, morphological and thermal properties of CuO nanoparticles as sputtering power is varied from 3080 W. The enhancement in sputtering power results the increase in size of particle with spherical type morphology from 10, 12 and 15 nm, respectively. The TG results indicate decreases in water content as a function of the sputtering power. Section 3.4 discusses about the effect of sputtering pressure (10-50 mTorr) on different properties of CuO nanoaprticles. The particles size increases from 6 to13 nm with enhancement of the sputtering pressure. TG pattern indicates that the nanoparticles are purely hydrous and weight loss was inversely correlated to the particle size. Chapter 4 presents the details of synthesis and characterization of tungsten oxide nanoparticles in relation to the different sputtering parameters. Section 4.1 gives a brief introduction about the tungsten oxide nanoparticles and the work performed by the different research groups contributed in the decontamination of CWA. Section 4.2 discusses the viii temperature effect on the structural, morphological and thermal properties of the sputter deposited tungsten oxide nanoparticles. The annealing temperature was varied from 200500 oC. XRD result confirmed formation of monoclinic phase and was further confirmed by the Raman spectroscopy technique. It was found that as the temperature increase, average crystallite size increases from 247 nm. On the other hand, the surface area and pore volume values decrease from 63.22 to 33.28 m2/g and 0.128 to 0.082 ml/g, respectively. These nanoparticles were used in the decontamination of 2-chloro ethyl ethyl sulphide (CEES) and dimethyl methylphosphonate (DMMP), well known simulants of sulphur mustard (HD) and sarin (GB), respectively. It was found that rate of degradation decreased from 0.143 to 0.109 h-1 and 0.018 to 0.010 h-1, for CEES and DMMP, respectively with increase in annealing temperature. Results indicates the role of hydrolysis reaction in the decontamination of CEES and DMMP. Section 4.3 exhibited the structural, morphological and thermal properties of WO3 nanoaprticles synthesized at 40, 60, 80 and 100 W power. The TG curve shows that the nanoparticles are purely hydrous with weight loss 10.9 % up to 300 ºC. Chapter 5 details the synthesis and characterization of zirconium oxide nanoparticles. Section 5.1 deals with the properties ZrO2 nanoparticles and highlights the work done by the various research group on their properties and their role to minimize the environmental problems. Section 5.2 describe the temperature effect on their structural, thermal and morphological properties using Powder XRD, FESEM, TEM, Raman spectroscopy, N2BET, TGA and FTIR techniques of ZrO2 nanoparticles and their efficiency for the decontamination of 2choro ethyl ethyl sulphide (CEES) and dimethyl methyl phosphonate (DMMP). XRD patterns indicate that the asdeposited nanoparticles are amorphous in nature and as the annealing temperature was increased from 300, 450 & 600 °C, they transform from tetragonal to monoclinic phase. The decontamination reactions exhibits pseudo first order kinetic behaviour with rate constant and half life values 0.1780.107 h-1 and 3.87-6.43 h for CEES and 0.0340.015 h-1 and 20.024-45.127 h for DMMP, respectively. The degradation occur through hydrolysis and elimination reactions. Section 5.3 describes the effect of sputtering power on structural, morphological and thermal properties at room temperature. The sputtering power was varied from 40 to 100 W followed by annealing at 350 ºC to obtain the crystalline properties. ix Chapter 6 details the synthesis and characterization of mixture of MnO2 nanoparticles and nanorods for the detoxification of 2choro ethyl ethyl sulphide (CEES) and dimethyl methyl phosphonate (DMMP). It gives a short discussion about the MnO2 nanoparticles and nanorods for the degradation of different type of CWA. It also highlighted the work of different research group over MnO2 synthesis. Thereafter, analysed was carried out by different techniques such as powder XRD, Raman spectroscopy, FESEM, TEM, BET, FTIR and Thermogravimetry (TG). The FESEM and TEM analysis confirms the formation of aggregates MnO2 nanoparticles and nanorods. Powder XRD and Raman results confirm the formation of pure tetragonal phase of MnO2 nanoparticles and nanorods. XRD and Raman spectroscopy confirms the formation of tetragonal phase. The decontamination reactions exhibited the formation of hydrolysis and surface bound products on the surface of nanoparticles and nanorods. The value of rate constant and half life was found to be 0.267 h-1 and 2.58 h for CEES and 0.068 h-1 and 10.10 h for DMMP, respectively. Chapter 7 details the synthesis and characterization of copper oxide nanoparticles. Section 7.1 gives introduction about the water pollution due to the presence of heavy metal ions in the water. Thereafter, discusses about different treatment and technology to minimize the water related problems. Section 7.2 deals with the copper oxides nanoparticles synthesis and their characterization for the adsorptive removal of Cr (VI) ions from aqueous solution. Different batch adsorption parameters such as solution pH, adsorbent dose, initial metal ion concentration, equilibrium contact time and temperature were used for the removal of Cr (VI) ions. The maximum adsorption capacity of Cr (VI) ion is 15.625 mg/g which was calculated using Langmuir isotherm model. The positive value of H indicates the endothermic nature of adsorption process whereas negative value of Gibbs free energy (G) indicates the spontaneous nature of Cr (VI) ions adsorption. The adsorption kinetics followed pseudo second order kinetic behaviour nature. Section 7.3 deals with the adsorptive removal properties of Pb (II) ions from aqueous solution. The characterization was carried out using powder XRD, FT-IR, Raman, FESEM, EDS, TEM, SAED, BET surface area, AAS techniques for the structural, morphological and adsorption properties. The optimum parameters were found to be pH 6, contact time 3 hours, adsorbent dose 2 g/L for 50 mg/L Pb (II) ion concentration. The adsorption kinetics follows pseudo second-order kinetic model which indicates that the adsorption controlled through chemisorption process. The adsorption isotherm follows Langmuir isotherm with maximum x adsorption capacity 37.027 mg/g. The S and H values were found to be positive which indicate the endothermic nature of adsorption process whereas negative value of Gibbs free energy (G) indicates the spontaneous nature of Pb (II) adsorption. Chapter 8 presents the summary and conclusion of the entire work presented in the thesis and also proposes the future directions in which these studies can be extended.