FUNCTIONALIZATION OF CUPROUS OXIDE NANOPARTICLES FOR PHOTOCATALYTIC ACTIVITY

Mohit Kumar Gachon University 2017 국내석사

The amino acids, namely L-glutamic acid and glucosamine were used as stabilising agents by a wet chemical method for the synthesis of Cu2O nanoparticles, where -NH2 groups attached through coordinated bonds with Cu2+ ions homogeneously. This procedure is a simple route to synthesize nanoparticles without high pressure, high temperature and a long period of time. Here, L-ascorbic acids can control the reduction of Cu2+ ions to Cu1+ ions in an aqueous solution at room temperature. Synthesised nanomaterial were confirmed by powder X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscope (SEM) and Transmission electron microscopy (TEM). In addition, these functionalized cuprous oxide nanoparticles exhibited excellent absorption properties in the visible light irradiation. The reasonably low priced cuprous oxide (Cu2O) nanoparticles are known as a p-type semiconductor and has a potential photocatalytic degradation activity of MB in aqueous solution. The contribution of invariant electron acceptor H2O2 increases the reaction rate of photocatalytic activity due to the formation of more OH* free radicals. The dye degradation proceeds with high rate constant value and the functionalised materials show good stability and reuse capability. In the second work, discuss about metal ions sensing by fluorometric technique using Zinc Oxide Nanowires. ZnO NWs were synthesized at low temperature by simple precipitation method. This modest to prepare ZnO NWs giving a convenient and reliable sensing of Cu (II) and Cr (VI) ions in useful application. A unique methodology relies from the coordination with ZnO nanowires. The concentration of copper and chromium were determined from decreasing in photoluminescence intensity at room temperature.

Metal-organic-framework derived transition metal embedded carbon for electrochemical energy storage and conversion

Kumar, Mohit Sungkyunkwan university 2021 국내박사

Transition metal embedded carbon derived from metal-organic-frameworks (MOFs) have drawn significant consideration when it comes to scientific study in the past few years owing to their beneficial effect of outstanding electronic conductivity, high porosity, and various applications. A massive efforts are committed to enhancing their physical/chemical properties, as well as constructing the unique morphology and carbon structure materials, also different materials composition with them, and so forth. In this thesis, transition metal embedded carbon materials derived from metal-organicframeworks are presented with a specific emphasis on their suitable application in energy storage and conversion (supercapacitor, hydrogen evolution reaction, and oxygen evolution reaction). However, the serious issue for the electrochemical energy conversion and storage is to establish a long durable electrode material because of the high energy and power density. Therefore, highly advanced electrode materials are required in favor of good efficiency in supercapacitor or for water splitting that could be industrialized applications. MOF have emerged as one of the most outstanding innovated and functional materials for electrochemical application. Herein, the first work of the thesis, we discuss the structure of novel MOFs-derived hierarchically porous Nickel@Carbon nanospheres (HP-Ni@C-N) synthesized via pyrolysis after the solvothermal reaction. Our method includes the decomposition of the trimesic acid as an organic molecule at a specific temperature of transformation into a carbon matrix wrapping of nickel nanoparticles (Ni NPs). Furthermore, we report HP-Ni@C-N supported on nickel foam as an electrochemical energy storage supercapacitor application and obtained 912 F g-1 at 10 mV s-1. Interestingly, the covalent bridge between the Ni core and carbon shell facilitates the faster ions transportation. Therefore, we presume that this work could informative and elucidative for the construction of MOFs-derived transition metals hybrid nanostructures. Further, engineering of transition metal sulfides with unique and desired structures for a specific application is a key challenge of today’s research community. In this work, carbon encapsulated nickel sulfide (Ni3S2@C) and N-doped carbon encapsulated Nickel sulfide (Ni3S2@NC) a complex hollow interior was synthesized. We employed an anion exchange approach in the course of annealing using solvothermally synthesized coordination polymer of nickel-trimesic acid (Ni-TMA) with and without melamine as a nitrogen precursor. The prepared hybrid materials showed ball-in-ball morphology and heazlewoodite mineral phase structure. Furthermore, the prepared materials were examined for electrochemical energy storage properties owing to its well-known faradaic dominant (battery-type) charge storage features and key positive electroactive material for today’s growing hybrid electrochemical capacitor. Among the prepared materials, Ni3S2@NC has demonstrated good electrochemical features like a specific capacity of 73.7 (57.1) mAh g-1 at 5 mV s-1 (2 A g-1) of scan rate (current density), the energy efficiency of 69%, and 54.4% of capacity retention even after 10,000 cycles. This work opens the opportunity to grow and employ specific structured materials for different applications. Moreover, cobalt embedded nitrogen-doped carbon is highly desirable for electrochemical energy conversion. However, it suffers from poor performance and instability in alkaline media due to the kinetically sluggish water dissociation (Volmer step). Herein, we present a facile approach for obtaining cobalt nanoparticles embedded N-doped carbon nanotube (Co@N-CNT) formed in the shape of yarn bundles. The use of Zeolitic-Imidazolate-Frameworks (ZIFs) is an easy approach to control and design due to the selective metal ions and the organic linker, and it converts into the desired structure/composite under different atmospheres. For the electrochemical hydrogen evolution reaction, Co@N-CNT sintered at 900 °C shows a lower overpotential of 196 mV to achieve a current density of 10 mA cm-2 along with no further drop with continued runs of 30 h stability cycles. In terms of performance, we believe that this work paves the way for an in-situ method of preparing transition metals and carbon composite structure synthesis for electrochemical energy applications. Lastly, facile and low-cost synthesis routes of highly competent catalyst materials for applications in oxygen evolution reaction are imperative. In this work, we synthesized bimetallic alloy crystals using nickel nitrate as a metal ions source and trimesic acid as an organic linker. Further annealing at an elevated temperature under a nitrogen atmosphere yielded alloy nanotubes textured nanoparticles. Numerous characterization techniques were used, revealing the bimetallic nature of the synthesized product. The product was a highly efficient and stable material for oxygen evolution reaction (OER) in an alkaline medium. In 1.0 M KOH solution, the copper nickel alloy with graphitic carbon (Cu3.8Ni@C) catalyst showed remarkable OER activity, obtaining an overpotential of 233 mV at a current density of 10 mA cm-2 with stability up to 18 hours under continuous electrolysis. Consequently, we believe that this work could contribute insights into lowcost electrocatalysts for OER.

The Hybrid Epithelial/Mesenchymal Phenotype and Its Implications in Cancer Metastasis

Jolly, Mohit Kumar ProQuest Dissertations & Theses Rice University 2016 해외박사(DDOD)

More than 90% of cancer-related deaths occur because cancer cells metastasize, i.e. invade the surrounding tissue, travel throughout the body, and form tumors at distant organs. Metastasis is often fueled by Epithelial-to-Mesenchymal Transition (EMT) that enables cells to migrate and invade, and its reverse Mesenchymal-to-Epithelial Transition (MET) that facilitates cells to shed migration and regain adhesion to colonize other organs. While undergoing EMT or MET, cells can adopt a hybrid epithelial/mesenchymal (E/M) phenotype through which they can both adhere and migrate, leading to collective migration as clusters of Circulating Tumor Cells (CTCs) that can be apoptosis-resistant and can initiate 50 times more tumors as compared to individually migrating CTCs. However, the hybrid E/M remains poorly characterized and has been tacitly assumed to be 'metastable' or transient. This study, through integrating mathematical modeling with wet-lab experiments, suggests that the hybrid E/M phenotype can be quite stable and its stability can aggravate tumor progression. First, we model the core regulatory network underlying EMT/MET---interconnected feedback loops among miR-34, miR-200, ZEB, SNAIL families---to predict that it can act as a 'three-way' switch enabling three phenotypes---epithelial (high miR-200, low ZEB), mesenchymal (low miR-200, high ZEB) and hybrid E/M (medium miR-200, medium ZEB). Second, GRHL2 and OVOL1/2 are predicted to stabilize a hybrid E/M phenotype and then confirmed experimentally in H1975 lung cancer cells that display a stable hybrid E/M phenotype. Third, modeling the interconnections of core EMT network with that regulating tumor-initiation potential (LIN28/let-7) predicts that a hybrid E/M, but not necessarily a fully mesenchymal, phenotype associates with higher tumor-initiation potential. Finally, integrating the core EMT network with intercellular Notch signaling, we predict that Notch-Jagged signaling can give rise to clusters of cells in a hybrid E/M phenotype. This prediction corroborates with our experimental observations that the drug-resistant tumor-initiating cells display elevated levels of Notch-Jagged signaling, reflecting the metastatic potential of hybrid E/M cells that can form clusters of CTCs. These results strongly argue that cancer cells in a hybrid E/M phenotype can be the key 'bad actors' of metastasis and identify novel targets---OVOL1/2, GRHL2 and JAG1---to curb metastatic load.

A Mechanized Error Analysis Framework for End-To-End Verification of Numerical Programs

Tekriwal, Mohit Kumar University of Michigan ProQuest Dissertations & Th 2023 해외박사(DDOD)

The behavior of physical systems is usually modeled by differential equations. For instance, the aerodynamics of airplanes is modeled by the Navier-Stokes equation; problems of optimal control are modeled by the Ricatti differential equation; and the valuation of stock options is modeled by the Black-Scholes equation. Thus, differential equations are pervasive in almost every aspect of science and engineering, and being able to solve them precisely and accurately, but also while trusting that the solutions are accurate, is of utmost importance. Since many of these differential equations are mostly difficult or intractable to solve analytically, they are typically solved numerically. This leads to an accumulation of errors at each approximation step. In the past, this accumulation of errors has led to catastrophic consequences like the failure of the Patriot missile system due to floating-point errors; and the infamous multi-million dollar loss in the Vancouver stock exchange due to accumulation of floating-point errors. It is thus important that we analyze each approximation error rigorously and formalize conditions which could lead to unexpected divergent behaviors of numerical solvers.In my thesis, I propose a mechanized error analysis framework, which treats errors from each approximation step modularly, in a formal setting like the Coq theorem prover. This framework connects a differential equation to the actual implementation of a linear solver for computing solutions to a differential equation. We show convergence of a finite-difference method, which is used to discretize the differential equation; compute an approximated solution to the discretized set of equations using stationary iterative methods, and prove its convergence formally in the field of reals. We then extend this analysis to a concrete implementation of a stationary iterative algorithm: Jacobi iteration, and prove correctness, accuracy and convergence of the implementation in the presence of floating-point errors. Our floating-point error analysis takes into account exceptional floating-point behaviors including overflow and underflow, and we prove the absence of overflow at each iteration by deriving concrete bounds on the input variables to the algorithm.Some of the important contributions of this thesis include: the formalization of a generic statement about convergence for finite-difference methods -- the Lax-equivalence theorem; the formalization of a generic statement about iterative convergence in the field of reals; the formalization of properties of the l2 and l∞ matrix and vector norms; norm-wise forward error bounds for matrix-vector operations in floating-point arithmetic; and the demonstration of a modular approach to achieve program verification on the Jacobi iteration method. This thesis further proposes ways to extend our end-to-end verification framework beyond Jacobi iteration to any stationary iterative method, and proposes ways in which automation could be achieved, as future extensions of this work.