2. Thesis and Dissertations
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Item Design, synthesis and investigation on optoelectronic properties of thiophene based heterocycles(National Institute of Technology Karnataka, Surathkal, 2020) K, Viprabha.; Dalimba, Udaya Kumar.The use of π–conjugated semiconducting materials in flexible and large–area optoelectronic devices is proliferated worldwide owing to the easy structural modifications and solution processability possible, leading to the change in opto– electronic properties. Most of the applications such as flexible displays and solid-state lighting sources based on organic light-emitting diodes (OLEDs) and nonlinear optical (NLO) devices are still in the developing stage due to the lack of ideal materials that exhibit the processability and an ability to interface with other materials. The research is continuing as ever to develop and characterize materials with large and fast optical responses which can satisfy different technological necessities. Furthermore, a definite correlation between the linear/nonlinear optical mechanism and the contribution of structure and nature of some thiophene based heterocycle is yet to be clearly interpreted. In this context, the present research work is focused on the design and synthesis of new class of thiophene based donor–acceptor (D–A) heterocycles for optoelectronic applications. A total of eighteen D–A type organic compounds were designed with various design strategies. They were successfully synthesized following appropriate synthetic protocols and characterized using different spectral analyses. The structureproperty relationships of the synthesized compounds were established by the optical absorption (UV–Vis), electrochemical (CV) and theoretical (DFT) studies. The third order NLO property i.e., the “effective two–photon absorption” of the compounds was confirmed by single–beam Z–scan analysis. The compounds VK3, VK8, VK10, VK12, VK13, VK14, VK15 and VK17 exhibit high nonlinear absorption coefficient (βeff) and a strong optical limiting behaviour. The preliminary studies on the electroluminescent properties of VK15 show that the molecule VK15 emits green light with low threshold voltage.Item Design, synthesis and characterization of chemosensors for determination of heavy metal ions(National Institute of Technology Karnataka, Surathkal, 2020) Tekuri, Venkatadri; Trivedi, Darshak R.Heavy metals such as Hg2+, Cd2+, Pb2+, As3+/As5+ are highly toxic because of clinical and environmental reasons. Here we have been designed and synthesized five new series of chemosensors for the colorimetric detection of heavy metal ions (Cu2+, Hg2+, Cd2+, Pb2+, As3+/As5+) and utilized for versatile applications of environmental concern. All the chemosensors have been characterized using different standard spectroscopic techniques like FT-IR, 1H-NMR, 13C-NMR and LC-Mass (ESI-MS). The selected chemosensors have been considered for three-dimensional structural elucidation using Single Crystal X-Ray diffraction (SCXRD) studies. The qualitative and quantitative, binding properties and detection limits for the developed chemosensors have been carried out using UV–Vis spectroscopic studies. The binding mechanism has been proposed based on UV–Vis titration and the same has been confirmed by FT-IR, 1H-NMR, LC-Mass and DFT studies. Among the synthesized chemosensors, the S4R1 showed a lower detection limit of 2, 11, 2, 7 ppb for Cu2+, Hg2+, Cd2+, Pb2+ ions, respectively. The S5R1 showed 8 ppb detection limit for As3+ ions, which is much lower than the WHO, US–EPA stated limit of 10 ppb. From the experimental and theoretical DFT results, it has been concluded that the simple organic molecules could act as very good colorimetric chemosensors for heavy metal ions such as Cu2+, Hg2+, Cd2+, Pb2+ and arsenate/arsenite ions. The S2R1 S3R3 and S3R4 showed brilliant analytical and environmental significant applications for the quantitative analysis of Cu2+, Cd2+, Hg2+ ion present in river, tap, and drinking water samples. The analytical method results of S3R3 and S3R4 for the determination of Cu2+ and Cd2+ indicates acceptable precision, linearity and accuracy of the developed method. Further, a good agreement found between proposed and wellestablished methods (AAS). The chemosensors S4R1–S4R3 and S5R1–S5R3 displayed colorimetric responses towards detection of heavy metal ions. S4R3 and S5R1 showed good naked eye response for the As3+/ As5+ ions. The S4R3 showed detection limit of 213 ppb for As3+ and the S5R1 displayed detection limit of 8 ppb/13 ppb for As3+/ As5+ ions. Further, successfully demonstrated the test strips applications.Item Corrosion Inhibition Studies of GA9 Magnesium Alloy in Chloride and Sulphate Media(National Institute of Technology Karnataka, Surathkal, 2020) Shetty, Sudarshana.; Shetty, A Nityananda.; Nayak, JagannathaThe corrosion behaviour of GA9 magnesium alloy in two different media, namely, sodium chloride and sodium sulphate in different concentrations and temperatures have been studied by potentiodynamic polarization and electrochemical impedance spectroscopy techniques. The effect of pH of the medium on the corrosion behaviour of GA9 magnesium alloy have also been studied in both the media. The results revealed a trend of higher corrosion rate associated with higher medium concentration, lower pH and higher temperature. The corrosion rate in the sodium chloride medium was higher than that in the sodium sulphate medium. Four different alkyl sulfonates namely sodium dodecylbenzenesulfonate (SDBS), sodium 4-n-octylbenzenesulfonate (SOBS), sodium 2,4-dimethylbenzenesulfonate (SDMBS) and sodium benzenesulfonate (SBS) were tested as corrosion inhibitors for GA9. The results pertaining to the corrosion inhibition studies of four inhibitors in two different media at different temperatures in the presence of varying concentrations of inhibitors are reported in the thesis. The inhibition efficiencies of all the four inhibitors decrease with the increase in temperature and increase in the concentration of the media. Activation parameters for the corrosion of the alloy and thermodynamic parameters for the adsorption of the inhibitors have been calculated and have been documented in the thesis. The sulfonates predominately physisorbed and adsorption was in accordance with Langmuir adsorption isotherm. The studied sulfonates were found to function as mixed type inhibitors. The sulfonates were more efficient at lower temperatures in both the media. Inhibition efficiency is in the order SDBS > SOBS >SDMBS > SBS. Proposed mechanism attributed the cathodic inhibition to the blockage of the reaction spots by chemisorbed sulphonates. The anodic inhibition resulted from the compaction of the porous film by precipitated magnesium sulfonates.Item Production of 5 - (Halomethyl) Furfurals from Cellulosic Biomass and their Synthetic Upgrading into Renewable Chemicals(National Institute of Technology Karnataka, Surathkal, 2020) Sharath, B. O.; Dutta, SaikatThe transportation fuels and most of the bulk and fine chemicals are primarily sourced from crude oil. However, the excessive use of crude oil has depleted the reserves, created a disparity between the demand and supply, and degraded the environment. In search of a renewable and preferably carbon-neutral source, biomass has found by many as a commercially-feasible replacement for fossilized carbon. The chemocatalytic valorization of biomass is of particular interest since they are fast, biomass agnostic, selective, and can potentially be integrated into the existing infrastructure. A major challenge in the chemocatalytic value addition of biomass is to develop a new generation of robust, selective, inexpensive, and environment-friendly catalysts that can selectively deconstruct the biopolymers. In this regard, the acidcatalyzed depolymerization and dehydration of biomass-derived carbohydrates (e.g., cellulose) into furanics is an elegant way of removing excessive functionalities from the carbohydrate. Biomass-derived 5-(hydroxymethyl)furfural (HMF), 5- (chloromethyl)furfural (CMF), furfural and levulinic acid (LA) have been used as renewable chemical building blocks for further value addition into fuels and specialty chemicals. In this thesis work, an improved synthesis of CMF and LA have been reported using aqueous HCl as the acid catalyst in the presence of quaternary ammonium chloride as a surface-active agent (SAA). The SAA afforded noticeably higher yields of CMF and LA compared to the control reactions. The reactions were optimized on various reaction parameters such as temperature, duration, loading of the substrate, and the loading of SAA. The SAA was successfully recovered and recycled. LA was converted into alkyl levulinates, a potential diesel additive and a renewable solvent, in the presence of phosphotungstic acid as an environment-friendly and recyclable catalyst. Alkyl levulinates were also prepared by the alcoholysis of CMF and furfuryl alcohol using HClO4-SiO2 as an inexpensive heterogeneous catalyst. A scalable and high-yielding preparation of 5-(alkoxymethyl)furfural, a novel fuel oxygenate, from CMF has also been reported.Item Molecular design and synthesis of diphenylamine based metal-free organic chromophores for dye sensitized solar cells (DSSCs)(National Institute of Technology Karnataka, Surathkal, 2020) K, Rajalakshmi.; Adhikari, A Vasudeva.Dye-sensitized solar cell (DSSC), which belongs to third generation solar cells has emerged as an attractive and promising low-cost solar device for harvesting solar energy. Grätzel and O’Brian invented DSSC in the year 1991, from that onwards it has been a promising technology attracted by both academic and industrial clad. Sensitizer is one of the vital components of DSSCs. It absorbs solar energy effectively to inject electrons into the TiO2 layer thereby producing electric energy. Here, sensitizer (dye) plays a crucial role in achieving high injection rate, thereby increasing the efficiency of the cell. Among the metalfree sensitizers n- type organic chromophores are of great importance. Even though, there are lots of studies on-going in this field, there is an ample scope for investigation of efficient sensitizers as they affect directly on PCE. Also, development of novel co-sensitizers for DSSCs sensitized with metal-based dyes, is an equally important area of research study. In this context, it was planned to design, synthesize and investigate the photovoltaic performance of new organic dyes based on diphenylamine as n-type sensitizers/co-sensitizers for DSSCs. Based on the detailed literature survey, twenty seven new n-type organic diphenylamine based sensitizers/co-sensitizers were designed using various molecular engineering strategies. They were successfully synthesized following appropriate synthetic protocols. Further, they were well-characterized by (FTIR, NMR and MS) spectral, optical and electrochemical analyses. The results revealed that, all the new dyes displayed the λabs and λemi in the range of 350-560 nm and 430-690 nm, respectively. Their band gaps were calculated to be in order of 1.90-3.09 eV. DFT study has been employed to optimize the molecular geometries and to apprehend the effect of structures of organic sensitizers/cosensitizers on their photovoltaic performances in devices. Also, TD-DFT simulations were carried out for the selected dyes. Finally, the synthesized dyes were subjected to the photovoltaic studies as sensitizers/co-sensitizers in DSSCs. Among newly synthesized organic sensitizers, the cell fabricated with D22 carrying cyanoacetic acid as an anchoring unit displayed the optimum PCE of 5.909 %. Whereas, the co-sensitization studies indicated that, under the same conditions, the device co-sensitized using D26 with HD-2 sensitizer showcased upheld PCE of 10.55 % showing an increment of 3.18 %. To sum up, by appropriately optimizing the molecular structures of organic chromophores, it is possible to further ameliorate the photovoltaic performance of the cells.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 Design and synthesis of new cyanopyridine based conjugated polymers for optoelectronic applications(National Institute of Technology Karnataka, Surathkal, 2020) P., Naveenchandra; Adhikari, A Vasudeva.Conducting polymers (CPs) have been widely investigated due to their several advantages over the traditional materials, such as wide and tunable electrical conductivity, facile production approach, high thermal stability, light-weight, low-cost and ease in material processing. Consequently, they are potential candidates for several applications in the field optoelectronics. In recent years, a great deal of interest has been focused on the synthesis of novel D-A configured conjugated polymers with desired properties through proper structural modifications, particularly for PLED application. In this context, the proposed research work has been aimed at design and synthesis of new D-A type conjugated polymers with improved photonic properties as good emissive materials. Based on the literature review, six new series of D-A type conjugated polymers (Series 1-6) carrying various electron donor and acceptor moieties have been designed with possible applications in PLEDs. Required bi-functional monomers have been prepared using appropriate synthetic procedures. Structures of new intermediates/monomers have been evidenced using spectral and elemental analyses. From these monomers, six new series of target polymers, viz. (i) phenylene-cyanopyridine based polymers having vinylene linkage as π-conjugated spacers, VPPy1-3 (Series-1), (ii) thiophene-cyanopyridine based polymers carrying vinylene linkage as π- conjugated spacers, VTPy1-3 (Series-2), (iii) phenylene-cyanopyridine based polymers containing phenylene as auxiliary donors, PPy1-3 (Series-3), (iv) thiophene-cyanopyridine based polymers containing phenylene as auxiliary donors, TPy1-3 (Series-4), (v) cyanopyridine based polymers carrying thiadiazole units, TDPy1-4 (Series-5), and (vi) heteroaromatic-cyanopyridine based polymers carrying imine linkage as π-conjugated spacers, Py1-4 (Series-6) have been successfully synthesized and their synthetic protocols have been established. Their structures have been confirmed by different spectroscopy and elemental analyses. Their molecular weights have been determined by GPC technique and thermal properties have been evaluated by TGA studies. Electrochemical properties have been studied using CV and photophysical properties have been evaluated by UV-visible absorption and PL spectroscopy. Their fluorescent quantum yields have been determined. Finally, their electroluminescence behaviour has been investigated. Most of the polymers have exhibited promising results in the device. Also, their structureproperty correlation studies have been carried out.Item Design, Synthesis and Characterization of Colorimetric Receptors for the Detection of Biologically and Environmentally Important Anions and its Applications(National Institute of Technology Karnataka, Surathkal, 2020) Singh, Archana.; Trivedi, Darshak R.Nature in its fullest form is a reservoir of biochemical processes regulated by various ionic species, which are primarily known to sustain ecological balance in the living system. Among them, anions such as fluoride (Fˉ), acetate (AcOˉ), dihydrogen phosphate (H2PO4ˉ), carbonate (CO32ˉ), arsenite (AsO2ˉ), arsenate (AsO42 ),־and dicarboxylates have a profound impact on human health, which are both beneficial and detrimental, depending on the amount present in the living system. Apart from the above anions detection, the detection of sodium fluoride and acetate ions in aqueous medium is important due its importance in household usage in the form of food, medicine, and cosmetics. Beyond an optimum amount, anions can lead to health issues. In this direction, the design and synthesis of artificial organic receptors has garnered great attention due to its ability to mimic molecular recognition at the physiological level. Owing to the profound utility of artificial receptors, this work focuses on the rational design of organic receptors, which can aid the colorimetric detection of anions. Seven different series of receptors based on various backbones, following binding sitesignalling unit approach, has been designed, synthesized, and characterized by standard spectroscopic techniques. The anion binding ability of the receptors is evaluated in appropriate solvent systems and confirmed by UV-Vis titration, 1H-NMR titration, Cyclic voltammetric, and DFT studies. The binding constant for the receptor-anion complex is calculated using the Benesi–Hildebrand equation. The binding mechanism is proposed based on UV-Vis titration and the same is confirmed by 1H NMR titration. The lower detection limit valves of the receptors achieved towards active anions signifies their efficacy in real- life application. Based on the experimental results, it is concluded that simple organic molecules can act as very good colorimetric receptors for biologically important anions such as Fˉ, AcOˉ, H2PO4ˉ, dicarboxylate, and CO32ˉ. Along with colorimetric detection, these receptors exhibited practical application such as detection of Fˉ ion in sea water, commercially available mouthwash and toothpaste, detection of AcOˉ ion in vinegar solution and test strip application.Item Application of Polyoxometalates as Efficient and Green Catalyst for Catalytic Upgrading of Cellulosic Biomass(National Institute of Technology Karnataka, Surathkal, 2020) Tiwari, Ritesh; Mal, Sib Shankar; Dutta, SaikatIn recent years, the research on the sustainable production of energy, transportation fuels, and materials has been incentivized. Non-food and preferably waste biomass has been identified as a commercially-feasible renewable alternative to fossilized carbons for producing fuels and chemicals. The chemocatalytic value addition of biomass, where the oxygen-rich biopolymers are selectively deconstructed into functionally-rich small organic molecules, is of particular interest. A new generation of robust, inexpensive, and environment-friendly catalysts are crucial for the chemocatalytic route. Over the past years, heteropolyacids (HPAs) are increasingly being used as a catalyst in the chemistry of renewables and biomass value addition. HPAs have been used in the hydrolysis and dehydration of pentose and hexose sugars in biomass into furfural and 5- (hydroxymethyl)furfural (HMF), respectively. Furfural, levulinic acid, and HMF act as renewable chemical building blocks that can be converted into commodity chemicals and materials via chemical or catalytic transformations. The proposed work is intended to explore the efficiency of various homogenous and heterogeneous HPA catalysts for the catalytic upgrading of biomass-derived chemical intermediates into value-added chemicals. HPA-based homogeneous and heterogeneous catalysts were used for the acetalization, esterification, and Baeyer-Villiger oxidation reactions of various biomass-derived chemical intermediates. The reaction conditions were optimized on various parameters such as temperature, duration, loading of reactant, and loading of catalyst. The cyclic acetals of biomass-derived furfural were prepared in high isolated yields in refluxing benzene in the presence of the phosphotungstic acid (PTA) catalyst. The PTA catalyst was successfully recovered and reused several times without significant loss in mass or activity. The esterification of saturated and unsaturated free fatty acids such as oleic acid and stearic acid were conducted in the presence of PTA catalyst as an efficient and recyclable catalyst. 2-Furanone was prepared by the selective oxidation of furfural using hydrogen peroxide as an inexpensive oxidant and PTA supported on ammonium zeolites as the catalyst. A scalable and high yielding preparation of alkyl benzoates and alkyl 2-furoates has also been reported.Item Synthesis and Characterization of Some Hydrophilic Polysulfone Based Membranes and their Application for Sustainable Water Purification(National Institute of Technology Karnataka, Surathkal, 2020) Ibrahim, G P Syed.; Isloor, Arun M.The intensifying obligation to clean, freshwater and declining obtainability from natural resources, water need to be conserved effectually to come across future requirements. This deteriorating condition fascinated the attention of global researchers towards nonconventional sources, such as ocean water, treated water and groundwater. Membrane separation processes have been established briskly in the past decade into the leading technology for effective water treatment. Among the commercially available polymeric membranes, polysulfone based membranes play an important role as it exhibits improved chemical, thermal and mechanical stability. However, the trade-off between permeability and solute rejection, reduced surface hydrophilicity and higher propensity towards fouling of polysulfone membranes urge further development. In this research work, polysulfone membrane performance was improved by incorporating hydrophilic polymeric nanoparticles and blending with hydrophilic polymers. The as-prepared composite or nanocomposite membranes were thoroughly characterized using analytical techniques. The nanocomposite hollow fiber ultrafiltration membranes were prepared with surface modified halloysite nanotubes, zwitterionic polymer nanoparticles and zwitterionically modified Fe3O4 demonstrated improved antifouling ability and dye rejection with higher permeability compared to the pristine membrane. The as-added nanoparticles not only increased the membrane surface porosity but also altered the surface hydrophilicity and charge. The polysulfone blend ultrafiltration membrane was fabricated, which exhibited enhanced heavy metal ions such as Pb2+ (91.5 %) and Cd2+ (72.3 %) rejection. To further improve the heavy metal rejection, thin-film composite/nanocomposite membranes were prepared. The as-prepared nanofiltration membranes demonstrated higher rejection of heavy metal ions such as Pb2+ (>98%) and Cd2+ (>95 %) and improved antifouling property.