Lakshminath Bezbaroa Central Library Digital Repository
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Recent Submissions
Thermoelectric Transport in Two-Dimensional Materials: Impacts of Structure, Composition, and Strain
(2025) Murari, Himanshu
Thermoelectric materials that can efficiently convert waste heat into electricity are crucial for sustainable energy technologies. Two-dimensional (2D) materials, owing to their quantum confinement effects and large surface-to-volume ratios, offer new avenues to overcome the coupled nature of transport properties that limit bulk thermoelectrics. Using first-principles density functional theory and Boltzmann transport calculations for electrons and phonons, the present thesis explores design strategies to enhance the thermoelectric figure of merit (ZT) by tuning structural symmetry, surface functionalization, strain, and chemical composition. The structural arrangement is found to strongly affect charge and phonon transport in hexagonal Si–X (X = N, P, As, Sb, Bi) monolayers, resulting in an improved ZT. In Janus MXenes (MM′CO₂), compositional asymmetry and surface modification enhance lattice anharmonicity, reduce lattice thermal conductivity, and improve electronic transport, effects that are further amplified under tensile strain. Similarly, Janus monochalcogenides (M₂XY and MM′X₂; M, M′ = Ge, Sn; X, Y = S, Se, Te) exhibit anisotropic band dispersions with high density of states near the band edges and multiple valleys, yielding large directional power factors and enhanced ZT. Finally, in monolayer h-NbN, inclusion of four-phonon scattering processes reveals strong phonon–phonon interactions that drastically suppress κₗ, increasing ZT by 2–3 times to about 1 at elevated temperatures. The study provides fundamental insight into how structural asymmetry, strain, and compositional engineering can be leveraged to optimize thermoelectric performance in 2D materials.
Studies on Power Generation in Water Lettuce (Pistia stratiotes) Assisted Sediment Microbial Fuel Cell
(2025) Dutta, Arup
Sediment microbial fuel cells (SMFCs) are emerging as a promising green energy technology with enormous application potential for wastewater treatment and linked electrical energy production. However, the practical application of these devices is challenged by their low-performance factors pertaining to the imbalanced electrolyte and oxygen levels and weak cathodic functions in open environment conditions. This study explored to address the poor performance of the SMFC by coupling it with a free-floating aquatic plant, Water lettuce. Growth of the plant balanced the catholyte pH in the range of 7.2–7.6, increased the ionic conductivity by 60%, stabilized the sub-surface water oxygen level, and boosted the cathodic potential by ~ 102 mV and ~ 49 mV in open and close circuit operations mode, respectively. The cumulative effect of these inputs led to producing a power density of 22.45 mW/m2 and a current density of 136.84 mA/m2 at 2 kΩ and 50 Ω loads, respectively. The enhanced cathodic performance was also attributed to the colonization of Water lettuce root bacteria as biofilm on the cathode that supported catalytic oxygen reduction on the graphite electrode. Metagenomic analysis indicated the biofilm is created mostly by aerobic microbes such as Ferrovibrio terrae, Comamonas aquatic, Achromobacter xylosoxidans, Hydrogenophaga taeniospiralis etc. bearing catalase enzyme, Pannonibacter phragmitetus, Streptococcus pyogenes, Streptococcus mutans etc. bearing heme enzyme and these microbes synergistically catalysed cathodic reduction reactions. This study demonstrated the positive role of Water lettuce in boosting the power performance of SMFC mainly by activating the cathodic functions of the setup. The progress of this innovative green energy technology destined for open environment applications is also mired by their inherent low voltage generation. A solution to improve the voltage level is to stack several unit cells through series or parallel connections. Paradoxically, such stacks frequently encounter voltage reversal (VR), which grossly affects their performance. Thus this study also presents strategy to mitigate VR in stacked water lettuce-assisted SMFCs (WL-SMFCs) by tuning the anodic surface area. A theoretical framework was first developed to relate electrical parameters to anodic surface area, predicting that increasing the anodic surface area of the terminal unit would enhance the overall stack voltage. This prediction was experimentally validated using a laboratory-scale stack of series-connected WL-SMFC units. When the anodic surface area of the terminal unit was increased to match the total anodic surface area of all other units combined, VR was significantly reduced. In two-, three-, and four-unit stacks, VR decreased by 70%, 57%, and 54%, respectively. Electrochemical impedance spectroscopic analysis confirms the corresponding increase in anodic storage charge (C) to 318.25±12.35 (670±26), 453.08±12.12 (964±26), and 422.92±9.39 (872±19) from the unit value of 240.58±25.65 (523±55) with respective capacitance (pF) values shown in brackets. This anodic surface area tuning approach offers a technically simple, self-sustaining, and cost-effective solution for alleviating VR, thereby enhancing the feasibility of SMFCs for open-environment applications. Herein, another effort has been made to increase the power output of plant- assisted sediment MFCs, using a power management system (PMS). Water lettuce-assisted sediment MFCs with a reactor volume of 500 ml were constructed, and four stacks were made, each with two cell units connected in series. When each of the stacks was connected to a charge pump, the voltage increased to double with an efficiency of 97.15±0.01%. The output of the four charge pumps was cascaded for charging a pair of 3300 μF capacitors, which were then discharged in series through a 0.5 F supercapacitor. With the input from the capacitors, the time for charging the supercapacitor was 35 hours that generated 3.5 V, which is ~61.5% of its maximum voltage limit (5.69 V). At the maximum operating point for the stacks (10 kΩ load), the PMS delivers ~0.92 mW, which is 7.13 times the total power delivered by the stacks. The maximum power conversion efficiency of the PMS was 81.76%. This study demonstrated powering a 1 W LED using the fabricated PMS. The power efficiency for the PMS can be further increased by allowing additional charging time for the supercapacitor and increasing the supercapacitor’s value. These results would be informative for designing a self-powered PMS topology to boost power in MFC stacks for their practical applications.
Molecular Cloning, Expression, Purification, Biochemical Characterization and Structure Analysis of a Novel Obligate Xylobiohydrolase (AcGH30A) from Acetivibrio Clariflavus ATCC 19732
(2025) Singh, Yumnam Robinson
The thesis includes a general introduction and literature review on xylan and xylan-degrading enzymes, followed by the cloning of the gene encoding the xylobiohydrolase (AcGH30A) from the Acetivibrio clariflavus genome. This study reports the biochemical and structural characterization of a novel GH30 xylobiohydrolase, AcGH30A, from Acetivibrio clariflavus. The gene was cloned in pET28a(+), expressed in E. coli BL21(DE3), and purified to homogeneity, revealing a ~58 kDa protein. AlphaFold2 modelling and SAXS analysis showed an α/β/α sandwich fold with Glu175 and Glu268 as catalytic residues. Molecular docking and molecular dynamics simulations confirmed high-affinity binding to xylobiose at subsites −1 and −2, supported by ITC (Ka = 7.83×10⁵ M⁻¹). AcGH30A displayed optimal activity at 80 °C, pH 7.0, stability from pH 4-7 and 30-70 °C, a melting temperature of 72 °C and a 21-day half-life at 4 °C. It hydrolysed various xylans exclusively to xylobiose, with highest activity against 4-O-methyl glucuronoxylan (Vmax = 139 U/mg, KM = 0.71 mg/ml). Enzymatic degumming of Boehmeria nivea (ramie) and Ananas comosus (pineapple leaf) fibres using AcGH30A alone or in combination with pectate lyase (CtPL1B) and mannanase (RfGH5_7) showed enhanced weight reduction and fibre smoothness. Dual-enzyme mixtures- AcGH30A + CtPL1B for ramie and CtPL1B + RfGH5_7 for PAL and the ternary mix showed superior performance. The enzymatic treatment yielded improved degumming efficiency and fibre mechanical properties. The thermostability, product specificity, and synergistic potential of AcGH30A highlight its potential for applications in the pulp, paper, and textile industries.
Layer-Controlled CVD Growth of 2D Tungsten Disulfide and Its Lateral Heterostructure with Molybdenum Disulfide for Optoelectronic and Biosensing Applications
(2025) Mia, Abdul Kaium
This thesis presents a comprehensive study on the layer-controlled CVD growth and multifunctional applications of WS2, MoS2, and in-situ WS2-MoS2 lateral heterostructures (HS). The 1L-WS2 exhibited excellent PL emission at room temperature, which was employed as a sensitive tool for the selective detection of Staphylococcus aureus in PBS and urine samples. Functionalization of 1L-WS2 with ssDNA aptamers enabled high selectivity, even in the presence of E. coli. For 2L-WS2, photodetection performance was evaluated through asymmetric contact engineering using metals with work functions both lower and higher than that of 2L-WS2, leading to unidirectional carrier flow. Compared to symmetric configurations, photodetectors (PDs) with asymmetric contacts demonstrated superior responsivity and detectivity. Thereafter, the influence of metal (Cr/Au) and non-metal (Bi2Se3) contacts on 1L-MoS2 was investigated. Devices with ultrathin Bi2Se3 contacts exhibited cleaner contact interfaces with lower defect density, leading to improved performance, achieving an on/off current ratio of 108, two orders of magnitude higher than their metal-contacted counterparts. The flexible 1L-MoS2 PD incorporating Bi2Se3 contacts also showed notable enhancements in responsivity, detectivity, and external quantum efficiency. Controlled in situ growth of WS2-MoS2 lateral HS was achieved by tuning the CVD growth parameters, enabling modulation of the relative areas of MoS2 and WS2 domains within single flakes. The diffuse interface induced interfacial strain, resulting in a fivefold increase in PL intensity from 2L-WS2 near the junction. When integrated as channels in back-gated FETs, these HSs demonstrated superior electrical performance, including enhanced on/off ratios and improved subthreshold swings. Finally, WS₂ quantum dots (QDs), coupled with Bi2O2Se nanosheets, were utilized for the selective detection of S. aureus. The QDs, functionalized with ssDNA aptamers, enabled detection even in the presence of other analytes.
Design Rationale of Expandable Pedicle Screws for Lumbar Spine
(2025) Sanjay, Devismita
Lumbar spine complications rank among the most prominent reasons for medical attention, especially for elderly subjects. Spinal fusion surgery is a common procedure to address some operative cases. Pedicle screw fixation is popular amongst the extensive range of spinal fusion developed. However, issues such as aseptic loosening, screw pullout, screw breakage, disposition of screws and pedicle fracture often lead to revision surgery. To reduce these problems, the concept of expandable pedicle screws came by with improved anchorage owing primarily to greater screw-bone interface. Clinically, they showed improved biomechanical fixation by facilitating bone growth around the fins, reducing strain shielding and promoting favourable bone remodelling. In this study, anatomically viable finite element (FE) models of a functional spinal unit (FSU) of intact L4-L5 vertebra were used to estimate stress-strain fields and the same were compared with FSUs instrumented with normal and expandable pedicle screws under different physiological loading conditions. The expandable pedicle screws predicted marginally improved anchorage with more contact area with the bone indicating improved stability. Greater area with peak stresses at the bone-screw interface indicated lesser stress shielding. Further, a strain energy density-based bone remodelling algorithm was employed on patient-specific lumbar FSU to investigate the bone density changes around the screws. Bone apposition was predicted near screw insertion region in L4 and L5 vertebra (for normal pedicle screws) and central anterior screw insertion region for both vertebra (for expandable pedicle screws). Bone resorption was predicted in posterior region, near screw length in L4, central anterior right side and posteriorly in L5 vertebra for normal pedicle screws. In context to bone remodelling, overall result favoured expandable pedicle screws over normal pedicle ones. Further, pullout tests were performed on three novel designs of expandable pedicle screws and thereafter, validated numerically. Next, two FE mechanoregulation based tissue differentiation algorithms were implemented to assess osseointegration for the three types of expandable pedicle screws. Six weeks post-surgery bone growth of 12-29% (load case 2) and 11-21% (load case 1), respectively, was predicted for the three types of screws. Type 3 (proximally coarse pitch screw) was estimated to have highest maximum pullout force (POF) and greater ossification among expandable pedicle screws with dual-threads.