Synthesis, Characterization and Applications of Metal Oxides Nanomaterials

Abstract

Among the metal oxides nanomaterials, Zinc oxide (ZnO), Titanium dioxide (TiO2), Vanadium pentoxide (V2O5) and Tin dioxide (SnO2) are the most promising candidates for exploring new applications in multiple fields. We have tried to resolve some important issues related to synthesis and integration of metal oxides nanostructure building blocks for large scale device applications. This dissertation mainly consists of three major parts, synthesis, characterization and applications of metal oxides based nanostructures. Metal oxides and their composites were successfully synthesized by applying solvothermal/hydrothermal and chemical methods associated with the co-precipitation technique. Through these techniques, various metal oxide nanostructures including TiO2 microspheres, hierarchical ZnO nanoflowers, plate-like TiO2 nanostructures, V2O5 nanowires, SnO2 cubic microcrystals, and Au/TiO2, (Au, Ag)-ZnO, Ag-TiO2 nanocomposites have been synthesized in controlled experimental conditions. Subsequently, the crystalinity and the microstructure of the nanomaterials were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) technique. The electronic interactions were confirmed by PL, DRS spectra and XPS studies. The composition and the elemental analysis were confirmed by EDS. The photocatalytic and electrochemical performances of these materials were also investigated. It is found that Au NPs supported TiO2 microspheres exhibit enhanced photocatalytic activity as compared to pure TiO2 microspheres. Moreover, the electrochemical properties of Au/TiO2/GCE modified electrode demonstrate the ability to electrocatalyze the oxidation of hydrogen peroxide and exhibit a rapid and sensitive response towards glucose detection at the low operating potential. The modified electrode shows a linear range from 1.0 to 15 mM with reproducible sensitivity of 1350 μA mM-1 cm-2 within less than 6 sec. The photocatalytic and electrochemical activity of Au/TiO2 composite provides a new platform for environmental remediation and biomedical applications. The results demonstrate that Au/TiO2 composite exhibits great prospect for developing efficient non-enzymatic biosensor and photocatalyst. Abstract xii It is observed that the noble metal NPs functionalized ZnO nanoflowers show enhanced photocatalytic activity than pure ZnO nanoflowers. Au-ZnO exhibits improved catalytic performance relative to Ag-ZnO. The composite also exhibits a strong interaction between noble metal NPs and ZnO nanoflowers. PL intensity of Au-ZnO nanocomposite is lower than Ag-ZnO and pure ZnO which is ascribed to the reduced recombination of free excitons resulting in enhanced photocatalytic activity. On the other hand, Ag-ZnO modified glassy carbon electrode shows good amperometirc response to hydrogen peroxide with linear range from 1 μM to 20 μM, and limit of detection of 2.5 μM (S/N = 3). The sensor also shows high and reproducible sensitivity of 50.8 μA cm-2 μM-1 with fast response of less than 3 s and good stability as compared to pure and Au-ZnO based sensors. The results elaborate that noble metal NPs functionalized ZnO nanocomposites exhibit a great prospect for the development of efficient non-enzymatic biosensor and as environmental remediators. Hydrothermally synthesized V2O5 NWs are found single crystalline and orthorhombic. The room temperature electrical transport properties reveal that complex impedance plane plot shows two overlapping semicircles which exhibits that the resistance from the oxygen vacancies and oxygen stoichiometric regions contribute to the overall transport behavior of V2O5 nanowires. The normalized functions suggest that the long range movements of the charge carriers are dominant at 100 Hz. The tangent loss (tan δ) is observed in accordance with the impedance plane plot. The ac conductivity σac shows substantial increase from 1×10-6—3×10-5 (S/cm2) in the frequency range of 5×103—105 Hz that may be attributed to a large number of charge carriers available for conduction by hopping. Structural, photocatalytic and electrochemical properties of hydrothermally synthesized SnO2 microcrystals have been performed. Microstructural analysis shows that uniform cubic crystals in the range of microns are formed. It is found that SnO2 microcrystals exhibit good photocatalytic performance towards RhB degradation. Electrochemical performance of modified glassy carbon electrode has been investigated using cyclic voltammetry, galvanostatic charge discharge, and electrochemical impedance spectroscopy in 1M H2SO4 electrolyte. These measurements reveal that SnO2 microcrystals exhibit excellent capacitive and surface charge storage behavior. The Abstract xiii measured specific capacitance is found to be strongly dependent on scan rate. The galvanostatic measurements and cycling stability demonstrate improved stability of the capacitor. Moreover the EIS measurements confirm the ideal characteristics of the capacitor. The present study shows that the attractive performance exhibited by SnO2 microcrystals make it promising candidate for high performance supercapacitors. The photocatalytic activity and the sensing capability of the pure anatase TiO2 and Ag NPs functionalized TiO2 plate-like nanostructures reveal that Ag-TiO2 nanohybrids exhibit an excellent photocatalytic activity towards model as well as textile dyes by completely degrading all the dyes in 15-18 min due to maximum UV absorption, large specific surface area, stability and catalytic activity of small Ag NPs compared to pure anatase TiO2 nanostructures. The Ag-TiO2 nanocomposites also show decrease in band gap energy compared to pure anatase TiO2. On the other hand, Ag-TiO2/GCE modified electrode shows good amperometirc response towards H2O2 with linear range from 2 to 30 mM and detection limit of 0.5 mM (S/N = 3). The sensor shows high and reproducible sensitivity of 32 μA mM-1 cm-2 with fast response of less than 3 s and good stability as compared to pure and TiO2/GCE. All these results illustrate that Ag NPs functionalized TiO2 nanostructures exhibit a great scenario for the development of efficient nonenzymatic biosensor and environmental remediator.