2. Thesis and Dissertations
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Item Photocatalytic Degradation of Dyes from Mixed Dye Contaminated Water using Visible Light Active Bismuth Ferrite@Tio2 and Bismuth Ferrite@Polyaniline Heterostructured Nanocomposites(National Institute of Technology Karnataka, Surathkal, 2021) K, Shankramma.; K, Vidya Shetty.The wastewater containing dye released from industries, when discharged to water bodies without any adequate prior treatment, ultimately leads to human health risk and threat to the environment. A proper wastewater treatment for Chemical Oxygen Demand (COD) and dye removal is essential. Photocatalysis with TiO2 which utilizes ultraviolet light, is a well-known treatment method for dye wastewater. The development of visible light active photocatalysts is gaining importance to harness solar energy. The present study reports the synthesis of bismuth ferrite@ titanium dioxide (BFO@TiO2), bismuth ferrite@polyaniline (BFO@PANI) heterostructured nanocomposites and their application in degradation of dyes from mixed dye contaminated water (MDCW) containing Methylene Blue (MB), Acid Yellow-17 (AY) and Rhodamine-B (Rh-B). The mixed phase BFO nanoparticles were synthesized by auto combustion method and were used in the synthesis of BFO@TiO2 and BFO@PANI. The synthesis/calcination parameters were optimized based on maximum photocatalytic activity in terms of degradation of dyes from MDCW. BFO@TiO2 particles synthesized with BFO:Ti molar ratio of 1:2, calcined at 400°C for 2 h (BFO@TiO2opt) and BFO@PANI particles synthesized with BFO: aniline molar ratio of 1:0.0041 (BFO@PANIopt) exhibited a maximum photocatalytic activity. The BFO@TiO2opt and BFO@PANIopt nanocomposites exhibited superior visible light assisted photocatalytic activity than BFO, TiO2 and PANI. BFO@TiO2opt and BFO@PANIopt nanocomposites were found to form core-shell heterostructures and exhibited a band gap energy of 1.2 eV and 1.4 eV respectively. The parameters such as pH, catalyst loading and light intensity were optimized to maximize dye degradation. The COD removal of 96.7% and 97% were achieved with BFO@TiO2opt and BFO@PANIopt, respectively. These particles were found to be very effective even under solar light. The presence and increasing concentrations of other dyes were found to decrease the degradation of a target dye. The COD removal followed Langmuir–Hinshelwood (L-H) kinetics. BFO@TiO2opt and BFO@PANIopt nanocomposites can be adopted for treatment of wastewater containing multiple dyes by harnessing solar energy for photocatalytic degradation.Item Studies on Porous Graphene, Oxides of Nickel and their Nanocomposites for Supercapacitor Application(National Institute of Technology Karnataka, Surathkal, 2021) Sethi, Meenaketan.; Bhat, D Krishna.The research thesis entitled ‘STUDIES ON POROUS GRAPHENE, OXIDES OF NICKEL AND THEIR NANOCOMPOSITES FOR SUPERCAPACITOR APPLICATION’ deals with the synthesis, characterization and studies on supercapacitor application of some oxides of nickel and their nanocomposites with porous graphene. The work describes successful synthesis of seven different kinds of novel electrode materials such as PG, NiO, NF, NC, PGNiO, PGNF and PGNC using solvothermal method. All the synthesized electrode materials were carefully characterized for their structural, elemental and morphological properties by employing appropriate techniques such as XRD, Raman, XPS, FESEM, TEM, HRTEM and BET techniques. The electrode materials were investigated for their utility in the field of supercapacitors using an aqueous 2 M KOH electrolyte. The synthesized electrode materials exhibited high electrochemical activity due to the synergistic effects of the components of the nanocomposite materials. The nanocomposite electrode materials displayed high cyclic stability at a higher applied current density. The impressive electrochemical accomplishment is attributed to the presence of porous structure and good surface area of composites, which not only acted as an ion-buffering reservoir but also maintained the mechanical strength during the continuous charge-discharge cycles. The obtained results suggest that these novel nanostructured oxides and PG based nanocomposites are potential candidates as electrode materials for the application in supercapacitors.Item Effect of Cosolvents and Ions on the Stability of Amino Acids, Peptides and Self-Assembled Peptide-Based Nanotubes(National Institute of Technology Karnataka, Surathkal, 2021) N, Dilip H.; Chakraborty, DebashreeThere lies a major challenge in molecular biophysics towards understanding the various biophysical processes and molecular dynamics (MD) simulations have been an imperative tool in elucidating it at the molecular level. In many biological processes, water plays a crucial role as a basic solvent. The existence of biological water in the vicinity of biomolecules has profound implications and is particularly important for the structural and biological functions of the biomolecules. The functioning of these biomolecules emerges from the delicate balance between various interactions of biomolecules with the solvent environment. This balance can be modulated by the addition of ions and small molecules known as cosolvents. Molecular-level understanding of how these cosolvents affect the solvation shell near the biomolecules is important for understanding the factors affecting the stability of proteins. The presence of both hydrophilic and hydrophobic moieties in amino acids facilitates its use as surfactant-like peptides which can be designed into well-defined nanostructures. These peptide nanostructures have wide applications in the bio-medical field. The water molecules near these nanostructures behave differently from the structural and dynamic point of view. In this context, the present research work is focused on investigating the effect of cosolvents and ions on the solvation structure of amino acids and peptides which results in the stability/de-stability of proteins. Studies were done on water molecules present near the interface and bulk region of these biomolecules and peptide nanotubes.Item Electrofabrication of Ni-Based Alloy Coatings for Better Corrosion Protection and Water Electrolysis(National Institute of Technology Karnataka, Surathkal, 2021) Shetty, Akshatha R.; Hegde, A Chitharanjan.This thesis titled, ‗Electrofabrication of Ni-based alloy coatings for better corrosion protection and water electrolysis ‗details a comprehensive approach for improving the corrosion resistance and electrocatalytic activity of (Ni-Co) and (Ni-Mo) alloy coatings through different advanced electrodeposition techniques. Inherent poor properties of alloy coatings, like corrosion resistance and electro catalytic activity of conventional (Ni-Co) and (Ni-Mo) alloy coatings have been improved by taking the advent of artificial convection of mass transport, by inducing ultrasound and magnetic field effect, during electrodeposition. The properties of sonoelectrodeposited (Ni-Co) coatings are improved further by developing them in multilayers, and by pulsing the ultrasound to go ON and OFF periodically, parallel to the process of deposition. The magneto-electrodeposited (Ni-Co) alloy coatings of higher corrosion resistance were developed by superimposing the magnetic field (B), in both intensity and direction (parallel and perpendicular), while depositing. The corrosion resistance property of electrodeposited (ED), sono-electrodeposited(SED), magnetoelectrodeposited (MED) and multilayer alloy coatings were evaluated in 5% NaCl solution through electrochemical AC and DC methods.The experimental investigation on corrosion behavior of all coatings demonstrated that magnetoelectrodeposited (Ni-Mo-Cd) alloy coating, represented as (Ni-Mo-Cd)6.0/0.3T is the most corrosion resistant, compared to other coatings. The electrocatalytic activity of electrodeposited (Ni-Co) and (Ni-Mo) alloy coatings, developed at different current densities (c.d.) were evaluated by alkaline water electrolysis in 1.0 M KOH, using them as both anode and cathode. Electrocatalytic efficacy, in terms of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) have been studied by measuring quantitatively the amount of H2 and O2 evolved. Effect of addition of nanoparticle into the alloy matrix found to increase the electrocatalytic activity of both (Ni-Co) and (Ni-Mo) alloy coatings, and results are discussed.The electro-catalytic efficacy of electrodeposited alloy coatings, having different configurations demonstrated that (Ni-Mo-CeO2)2.0 Adm-2 and (Ni-Mo) 2.0 Adm-2 coatings are the most active electrode materials for HER and OER, respectively. The electrocatalytic kinetic parameters of HER and OER, corresponding to different alloy/composite coatings were evaluated through cyclic voltammetry (CV) and chronopotentiometry (CP) methods. A mutually opposite electrocatalytic activity of both (Ni-Co) and (Ni-Mo) alloy coatings towards HER and OER, with deposition c.d.‘s was observed. It was attributed to the change in composition of the alloys, in terms of their constituting metals content, in the deposit.The changed property of alloy coatings, both corrosion and electrocatalytic activity was found to have a close relationship with their composition, phase structure, surface morphology and roughness, confirmed by EDX, XRD, SEM and AFM analyses, respectively. The experimental data are compared, and results are discussed with Tables and Figures, and a note for future work is mentioned at the end.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.