Please use this identifier to cite or link to this item: http://localhost:8081/xmlui/handle/123456789/1511
Authors: Pandey, Ashish Kumar
Issue Date: 2009
Abstract: NanocrystaUine thin films and nanopowders of metal oxides have attracted considerable attention during last decade due to their applications in gas sensing, electrochemical and biosensing and in making optical switches, windows for solar cell, thin film batteries and photocatalysis etc. In recent years interest in the field of nanotechnology and nanocrystalline materials of these oxides has been continuously growing. This is because of the advancements in the various characterization technologies which had made it possible to formulate smaller device components, thereby improving the performance of devices without increasing their physical size. Despite numerous scientific works, new routes of fabrication and the fundamental understanding of these materials are essential so that they can be integrated into contemporary and emerging technologies. Therefore, it is desirable to develop the processes for producing the nanomaterial oxides of high quality at low cost. The objective of the present work was to synthesize nanocrystalline thin films of Iron oxide using low cost ultrasonic spray pyrolysis and pulsed laser depositon technique. In addition mist chemical vapor deposition technique (UM-CVD) was used to synthesize nanopowders of iron oxide and titanium dioxide. The applications of these films/ nanopowder have also been explored in the modification of electrode surfaces to enhance their catalytic activity in electrochemical sensing of some biologically important compounds. Further, the applications of fullerene (C6o) in the electrode modification and its uses in the quantitative determination of some drugs, which are banned by the World Anti Doping Agency (WADA), have also been studied. A chapter- wise summary of the thesis is given below. Chapter 1 gives an overview of nanomaterials and an introductory background of related materials. The chapter is comprised of the discussions on the various chemical and physical properties of the iron and titanium oxides and fullerene. The frequent use of these nanomaterials in the various chemical and biosensing applications has also been described. The last section of this chapter presents the basic description about the different electroanalytical techniques used during the investigations. Chapter 2 presents the description of the various instruments and experimental techniques, which are used for the preparation of the nanocrystalline oxide thin films and nanopowders and their characterization for different properties. The description about the setup of Ultrasonic Spray Pyrolysis and Ultrasonic Mist-Chemical Vapour Deposition (UMCVD) technique developed in our laboratory, for the growth of metal oxide nanocrystalline thin films and nanopowders have also been presented. The basic principle and the working of Pulsed laser deposition (PLD) technique used in the synthesis of iron oxide thin films on various substrates is presented in the next section. The details of various characterization techniques used for the structural [X-ray diffraction (XRD), Field Emission Electron Microscopy (FESEM), Transmission Electron Microscopy (TEM) and Atomic Force Microscopy (AFM)], optical [UVvisible spectroscopy] and magnetic [SQUID] properties of the nanocrystalline thin films and nanopowders have been summarized in the present chapter. The procedure used in the electrochemical analysis of various biomolecules using Bioanalytical system (BAS CV- 50W) at different modified working electrodes is also presented. Chapter 3 describes the growth and characterization of nanocrystalline iron oxide thin films and their applications in electrochemical sensor. This chapter is divided into two sections. The first section mainly describes the growth and characterization of iron oxide nanocrystalline thin films via ultrasonic spray pyrolysis. The effect of substrate temperature on structural and optical properties was investigated. The films were deposited on quartz substrates at different deposition temperature in the range 400- 700 °C. Both orientation and size of crystallites were found to depend on the substrate temperature. The XRD results of nanocrystalline thin films revealed the magnetite to hematite phase transformation with increase in substrate temperature. The morphological characterization of these films by Field emission scanning electron microscopy and Atomic force microscopy showed a grain growth from needle to plate like shape and size distribution in the range of 50-100 nm. The deposited thin films exhibited the estimated direct band gap (Eg) in the range 2-2.2 eV. It was observed that n the thin films deposited on quartz substrate at different temperatures had low conductivity and thus are not suitable for electrochemical sensing. The second section deals with the synthesis of iron oxide nanocrystalline magnetite thin films on various substrates by pulsed laser deposition technique using excimer KrF laser (248 nm). Both the nature of substrate and deposition temperature was found to have great impact on the structural and magnetic properties of these films. Interestingly, the preferred orientation of the films grown on Si (100) and quartz substrates was found to change from (222) & (311) to (400) with increase in substrate temperature. However, the films deposited on MgO (100) substrate exhibited a- axis orientation with highly intense (400) reflection in XRD pattern. Measurements of variation in magnetization with increase in magnetic field (M-H) at constant temperatures of 5K and room temperature show the ferromagnetic behavior of magnetite films. Further it was investigated that the coercivity, remanent magnetization and saturation magnetization of the films were strongly dependent on substrate nature and temperature. Chapter 4 describes the work carried out on the synthesis of iron oxide nanocrystalline powder by Ultrasonic mist chemical vapor deposition (UM- CVD), which is a promising method for large area deposition at low temperatures taking in to account of its simplicity, inexpensiveness and safety. The synthesized nanopowder has been found to possess pure hematite structure with intense (104) reflection and with lattice parameter a - 1.418A & c = 5.363A at room temperature. The results of in-situ high temperature X-ray diffraction in vacuum for Fe2C>3 nanopowder from room temperature to 1100 °C showed a clear phase change withan increase in crystallite size with increasing temperature. The excess free volume associated with the grain boundaries was calculated and was found to decrease with increase in crystallite size. The surface morphology and particle size distribution of Fe203 nanopowder were characterized using field emission scanning electron microscope (FE-SEM) and high resolution transmission electron microscope (HR-TEM), which revealed that the particles were spherical in nature and distributed in range of 50-100 nm. SQUID magnetometry results indicate the ferromagnetic nature of the nanopowder with crystallite size of 6 nm as calculated from M-H curve. Transmittance of approximately in 55% and estimated direct band gap of 2.5 eV was observed. Further, the nanopowder was used to modify glassy carbon electrode (GCE) and the modified electrode was found to exhibit electrocatalytic activity for the oxidation of dopamine. It is expected that the nanopowder will exhibit promising applications in the development of sensors. Chapter 5 discusses the growth and characterization of nanocrystalline anatase Ti02 nanopowder by cost effective Ultrasonic mist chemical vapor deposition (UM- CVD) technique and is used for the fabrication of modified glassy carbon electrode which is employed for the determination of dopamine in the excess of ascorbic acid/ uric acid using osteryoung square-wave voltammetry. The voltammograms obtained during the oxidation studies revealed that due to its better catalytic function towards the oxidation of dopamine and ascorbic acid/uric acid, the overlapping voltammetric response of all the biomolecules at the bare electrode is resolved into well defined voltammetric peaks with lowered oxidation potential and enhanced oxidation currents. Linear calibration curves for dopamine are obtained over the concentration range 75 nM - 2.5 uM in 0.1M phosphate buffer solution at pH 7.2 with a correlation coefficient of 0.9940 and the detection limit (3a) is estimated to be 13.8 nM. The structural characterization of nanopowder by high temperature XRD clearly shows the phase transformation from anatase to rutile phase on increasing temperature. The morphological structure is characterized by FESEM and HRTEM and it revealed that the particles are spherical in nature with size 50- 100nm. The transmittance spectra of nanopowder, was observed to exhibit 85%transmittance on the average with a sharp fall at wavelengths shorterthan 360 nm, corresponding to the energy threshold for band edge absorption. The band gap of the prepared titania nanopowder was calculated using absorption spectrum and was found to be -3.3 eV. Chapter 6 discusses the application of fullerene in the modification of glassy carbon electrode for the determination of some important drugs which are used by the athletes in competitive games. As these drugs are banned by the world anti doping agency (WADA), hence their determinations at very low concentration level are of much importance. In the first section of the chapter the electrochemical behavior of methylprednisolone (MP) at the fullerene-C6o-modified glassy carbon electrode has IV been investigated using differential pulse voltammetry. The experimental results suggest that the modified electrode exhibits electrocatalytic effect on the oxidation of MPresulting in a marked enhancement of the peak current response. Underthe selected conditions, the oxidation peak current was linearly dependent on the concentration of MP in the range 5.0nMto 1.0 uMwith a sensitivity of 0.0107 uA uM"1. The detection limit was estimated to be 5.6 nM. The electrode showed good sensitivity, selectivity, stability and reproducibility. In addition, the developed method was satisfactorily applied to the determination of MP in pharmaceutical formulations and human serum and urine samples without any necessity for sample treatment or time-consuming extraction steps prior to the analysis. A comparison of observed results with GC-MS indicated a good agreement. The second section of the chapter describes a new method for the determination of salbutamol using fullerene C6o-modified glassy carbon electrode. The presence of graphite and metallic impurities in C6o are found to diminish the peak. The oxidation of salbutamol was observed in a single well-defined, diffusioncontrolled process using square wave voltammetry. The peak potential of oxidation peak was dependent on pH and determination was carried out at physiological pH 7.4. The peak current versus concentration plot was linear in the range 100-2000 ng/ml of salbutamol. The detection limit was found to be 40ng/ml. The determination of salbutamol was carried out in human blood and urine samples and common interferents such as dopamine, ascorbic acid and uric acid do not interfere. The method proved to be specific, rapid, and accurate and can be easily applied for detecting cases of doping. A cross-validation of the observed results with GC-MS indicated a good agreement.
Other Identifiers: Ph.D
Research Supervisor/ Guide: Kaur, Davinder
Goyal, R. N.
metadata.dc.type: Doctoral Thesis
Appears in Collections:DOCTORAL THESES (chemistry)

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