2. Thesis and Dissertations
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Item Even D- Carbon Nanostructures for Sensing and Energy Applications(National Institute of Technology Karnataka, Surathkal, 2020) Mishra, Praveen.; Bhat, B Ramachandra.The thesis titled “Even-D Carbon Nanostructures for Sensing and Energy Applications” encompass the work on Even-D carbon nanostructures, particularly graphene and graphene quantum dots for the prospective use as materials for sensors and photovoltaic devices. A new route to obtain the quantum dot by bombarding the graphene oxide (GO) sheets with the swift heavy ions is discussed. The graphene quantum dots (GQD) in their native state were found to be highly useful in determining the metal cations like Ca2+, Cu2+, and Co2+. The determination of Ca2+ ions in the water was quantitatively possible in the presence of interfering ions such as Al3+, Na+, and K+. However, the detection of transition metals with GQD remains only qualitatively feasible, because transition metals non-selectively quench the PL of GQD. The amine functionalized GQD (NH2-GQD) made the quantitative determination of glucose possible via aggregation induced photoluminescence enhancement with an accuracy of 98%. The NH2-GQD-GO composite proved to be an active material for the electrochemical determination of oxalic acid within 0.5 mM to 55 mM and a limit of detection of 50 μM. The NH2-GQD were also demonstrated to be an excellent cosensitizer for the hybrid quantum dot solar cell when used in conjunction with anthocyanin dye. The photosensitizer combination improved the photon conversion efficiency by ~50%. Significant raise in other parameters was also observed. The work presented in this thesis demonstrates the utilization of the excited electron resulted by the electromagnetic irradiation on the GQD. It is evident that the energy emitted by the electron returning to the ground state is utilized for photoluminescent detection of various analytes. The extraction of excited electron through electrochemical means resulted in making GQD based electrochemical sensors and co-sensitizers in the photovoltaic devices.Item Synthesis, optimization and investigation of properties of BaO-P2O5 and BaO-CaF2-P2O5 glasses with and without silver nanoparticles(National Institute of Technology Karnataka, Surathkal, 2017) N, Manoj Kumar; Shashikala, H. D.This thesis reports synthesis, optimization and investigation of properties of metaphosphate BaO-P2O5 and BaO-CaF2-P2O5 host glasses and these glasses embedded with silver nanoparticles. Host glasses were prepared by conventional melt-quenching technique. Taguchi based grey relational analysis was used in the present study to simultaneously optimize the multiple performance characteristics of CaF2 added ternary barium phosphate glasses. This method helped to obtain optimal parametric combination for best performance characteristics of samples with minimum number of experiments. The investigated physical, structural, mechanical, optical and thermal properties of samples indicated that these properties strongly depended on CaF2 content. The sample with optimized composition, 30 mol% BaO–20 mol% CaF2–50 mol% P2O5 showed improved physical, elastic, mechanical, optical and thermal properties with thermal stability parameter above 100 ◦C. Hence, the above mentioned glass is suitable for fiber fabrication. Glasses doped with silver oxide and tin oxide were prepared by conventional melt-quenching technique but following a different synthesis route, in which silver nanoparticles of different sizes were embedded upon subsequent heat treatment at different temperatures and time durations. The formation, growth and distribution of silver nanoparticles in the glass matrix appeared to be both temperature and time dependent. Evolution in optical properties of prepared glasses were examined to understand the mechanism of cluster development and growth of silver nanoparticles. Size, morphology and distribution of embedded silver nanoparticles in the glass matrix were investigated using transmission electron microscope (TEM). Noticeable improvement was observed in elastic and mechanical properties of glass-metal nanoparticle composite with increase in concentration and size of embedded nanoparticles, which could be attributed to the improvement in strength of glass matrix and ease of plastic flow.