Chemistry Commons^™

First Principles Calculations To Investigate Surface And Catalytic Properties Of Materials For Green Energy Generation, Keerthan Raghavendra Rao

Theses and Dissertations--Chemistry

Climate change due to greenhouse gas build up in the earth’s atmosphere is an existential threat to humanity. To mitigate climate change, a significant shift from fossil fuels is necessary. Over the years, several renewable energy sources like solar, wind, geothermal etc. have been explored with the aim providing carbon-free energy. In this work, we focus on using density functional theory (DFT) methods to investigate key functional properties of materials of interest for applications in solar cells and catalytic conversion for energy generation. We show geometric effects of carboxylic acid binding on a transition metal surface to impact the deoxygenation …

Water-Soluble Palladium, Copper, And Nickel Catalysts And Their Formation In Ligand-Free Suzuki-Miyaura Cross-Coupling Reactions, Priya Karna

Theses and Dissertations--Chemistry

Transition-metal catalyzed Suzuki-Miyaura (SM) cross coupling is a powerful synthetic method for constructing carbon-carbon and carbon-heteroatom bonds in designing organic compounds, agrochemicals, pharmaceuticals, and precursors for materials. However, the nature of catalysis and identity of the transition metal catalysts used in these reactions remain under debate or unknown. This dissertation reports the studies of three metals: Pd, Cu, and Ni. Pd-nanocluster catalysts and their formation in ligand-free SM reactions with Pd(II) nitrate as a precatalyst was investigated. The catalysts are water-soluble neutral Pd tetramer and trimer in their singlet electronic states as identified by UV-Vis absorption spectroscopy and are formed …

Translating Chemistry, Structure, And Processing To The Solid-State Morphology And Function Of Organic Semiconductors Through Computational Modeling And Simulations, Chamikara D. Karunasena

Theses and Dissertations--Chemistry

The immense synthetic design space and material versatility have driven the exploration and development of organic semiconductors (OSC) over several decades. While many OSC designs focus on the chemistries of the molecular or polymer building blocks, a priori, multiscale control over the solid-state morphology is required for effective application of the active layer in a given technology. However, molecular assembly during solid-state formation is a complex function interconnecting the building block chemistry and the processing environment. Insufficient knowledge as to how these aspects engage, especially at the atomistic and molecular scales, has so far limited the ability to predict …

Surface Modification Of Carbon-Based Electrodes For Electrochemical Conversion Processes: Oxygen Reduction Reaction And Bicarbonate Conversion, Udari Shyamika Kodithuwakku Arachchige

Theses and Dissertations--Chemistry

Oxygen reduction reaction (ORR) and conversion of bicarbonate into value-added chemicals are two significant electrochemical processes for energy storage and conversion. ORR is an important electrochemical reaction in fuel cells and metal-air batteries that provide power conversion and storage capacity, respectively, for portable electronics, and electric vehicles. However, the performance of catalysts (e.g., platinum-based) is critically limited by slow kinetics, inefficient four-electron pathway, and surface deactivation. This limited performance of platinum-based catalysts, the scarcity of platinum, and vulnerable supply chains for critical minerals require the development of alternative electrocatalysts now more than ever. Carbon-based materials possess several key properties that …

Developing And Deploying Data-Driven Tools For Accelerated Design Of Organic Semiconductors, Vinayak Bhat

Theses and Dissertations--Chemistry

Organic semiconductors have gained widespread attention due to their potential applications in flexible, low-cost, lightweight electronics, energy storage and generation technologies, and sensing applications. However, developing new organic semiconductors with improved performance remains a significant challenge due to the vast chemical space of possible molecular and materials structures. Furthermore, the high cost and time-consuming nature of experimental synthesis and characterization hinder the rapid discovery of new materials. To overcome these challenges, this dissertation presents a data-driven approach to organic semiconductor discovery. The primary focus of this work is the development of data-driven tools, namely machine learning models, to predict critical …

Determining Material Structures And Surface Chemistry By Genetic Algorithms And Quantum Chemical Simulations, Josiah Jesse Roberts

Theses and Dissertations--Chemistry

With the advent of modern computing, the use of simulation in chemistry has become just as important as experiment. Simulations were originally only applicable to small molecules, but modern techniques, such as density functional theory (DFT) allow extension to materials science. While there are many valuable techniques for synthesis and characterization in chemistry laboratories, there are far more materials possible than can be synthesized, each with an entire host of surfaces. This wealth of chemical space to explore begs the use of computational chemistry to mimic synthesis and experimental characterization. In this work, genetic algorithms (GA), for the former, and …

Plasmon Enhanced Single Molecule Fluorescence In Zero Mode Waveguides (Zmws), Abdullah Masud

Theses and Dissertations--Chemistry

Plasmonic nanostructures are an extensive research focus due to their ability to modify the photophysical properties of nearby fluorophores. Surface plasmons (SP), defined as the collective oscillation of delocalized electrons, are the fundamental characteristic primarily responsible for altering those photophysical properties. Studying fluorophores at the single-molecule level has received significant attention since more specific information can be extracted from single molecule-based studies, which otherwise could be obscured in ensemble studies. However, single-molecule studies are inherently challenging because the signal from a single molecule is usually dim, making it difficult to detect. The situation is even worse in a crowded environment …

Laser Ablation In Liquid For The Controlled Production Of Photoluminescent Graphene Quantum Dots And Upconverting Nanoparticles, Rosemary Lynn Calabro

Theses and Dissertations--Chemistry

Photoluminescent­ (PL) nanomaterials play an important role in areas including displays, sensing, solar, photocatalysis, and bio applications. Traditional methods to prepare PL materials suffer many drawbacks such as harsh chemical precursors, complicated synthetic steps, and production of many byproducts. Laser ablation in liquid (LAL) has emerged as a promising alternative to prepare materials that is single-step, fast, uses fewer precursors, produces fewer side products, and has simple purification steps. During LAL, a solid target is irradiated with a pulsed laser source. The laser pulses cause plasma plumes of the target material to form which are cooled, condensed, and can react …

Threshold Ionization Spectroscopy And Spin-Orbit Coupling Of Lanthanide Complexes, Yuchen Zhang

Theses and Dissertations--Chemistry

The C-C and C-H bonds have high bond strength and low polarization, which make many small hydrocarbons too inert to react with other molecules under ambient pressure and temperature conditions. Therefore, activation of these bonds is required to convert such small molecules into other value-added chemicals. Among various bond activation methods, metal activation is widely used and reported in the literature, because of its relatively mild reaction conditions and high selectivity.

In this work, Ce atom reactions with several small hydrocarbons are carried out in a pulsed laser vaporization supersonic molecular beam source, and Ce -hydrocarbon species are observed with …

Towards The Rational Design Of Organic Semiconductors Through Computational Approaches, Qianxiang Ai

Theses and Dissertations--Chemistry

Though organic semiconductors have illustrated potential as industry-relevant materials for electronics applications, there are few guidelines that can take one from molecular design to functional materials. This limitation is, in part, due to incomplete understanding as to how the atomic-scale construction of the π-conjugated molecules that comprise the organic semiconductors determines the nature and strength of both the noncovalent intramolecular interactions that govern molecular conformation and noncovalent intermolecular interactions that regulate the energetic preference for solid-state packing. Hence, there remain several fundamental questions that need to be resolved in order to design organic semiconductors from a priori knowledge, including: What …

Designing Metal-Halide Perovskites With Enhanced Optical Properties And Stability Using Surface Ligands, Md Aslam Uddin

Theses and Dissertations--Chemistry

Metal-halide perovskites (MHPs), with formula ABX₃ (A = methylammonium, formamidinium, or Cs⁺; B = Sn²⁺ or Pb²⁺; and X = Cl^-, Br^-, or I^-) are versatile and attractive materials because of their tunable optical and electronic properties. These optical and electronic properties include tunable direct band gaps, high absorption coefficients, low exciton binding energies, relatively high electron and hole mobilities, narrow emission line-widths, and high photoluminescence (PL) quantum yields (Φ_PL). Much of the initial excitement around organic metal-halide perovskites focused on their application in photovoltaics (PVs) …

Structure, Surface, And Interfacial Modifications Of Carbon And Supported-Metal Electrodes For Electrochemical Carbon Dioxide Conversion, Namal Wanninayake

Theses and Dissertations--Chemistry

Currently, the global emission of greenhouse CO₂ is over 36 billion tons per year. Consequently, the atmosphere's CO₂ concentrations have exceeded 400 ppm, which is the highest reported in the last three million years. The accumulation of CO₂ is the most critical origin for today's climate change; thus, closing the carbon cycle is vital to reverse the detrimental impacts of climate change. Under this goal, the electrochemical reduction of CO₂ into commodity fuels and chemicals via renewable energy is one of the most promising strategies to recycle CO₂. Despite significant progress made in electrocatalysis, …

Multiscale Modeling Of Structure-Function Relationships Of Organic Semiconductors, Shi Li

Theses and Dissertations--Chemistry

While optoelectronic devices built from organic semiconductors (OSC) continue to find their way into the commercial landscape, there remain numerous challenges to overcome to supplant traditional semiconductors in many technologies. Chief among these are low performance metrics relative to devices with conventional semiconductors and device stability. In order to overcome these challenges, a wide range of new OSC and processing technologies have been developed. However, there remains limited fundamental understanding of the relationship between molecular structure, packing in the solid state, and the resulting materials properties. Here, we make use of multiscale molecular models and utilize classical all-atom molecular dynamic …

Carbon Quantum Dots: Bridging The Gap Between Chemical Structure And Material Properties, Timothy J. Pillar-Little Jr.

Theses and Dissertations--Chemistry

Carbon quantum dots (CQDs) are the latest generation of carbon nanomaterials in applications where fullerenes, carbon nanotubes, and graphene are abundantly used. With several attractive properties such as tunable optical property, edge-functionalization, and defect-rich chemical structure, CQDs have the potential to revolutionize optoelectronics, electro- and photocatalysis, and biomedical applications. Chemical modifications through the addition of heteroatoms, chemical reduction, and surface passivation are found to alter the band gap, spectral position, and emission pathways of CQDs. Despite extensive studies, fundamental understanding of structure-property relationship remains unclear due to the inhomogeneity in chemical structure and a complex emission mechanism for CQDs.

This …

Spectroscopy And Formation Of Lanthanum-Hydrocarbon Complexes, Wenjin Cao

Theses and Dissertations--Chemistry

Lanthanum-mediated bond activation reactions of small hydrocarbon molecules, including alkenes, alkynes, and alkadienes, were carried out in a laser vaporization metal cluster beam source. Time-of-flight mass spectrometry and mass-analyzed threshold ionization (MATI) spectroscopy, in combination with quantum chemical and multi-dimensional Franck-Condon factor calculations, were utilized to identify the reaction products and investigate their geometries, electronic structures, and formation mechanisms.

La-hydrocarbon association was only observed in the reaction of La with isoprene. C-H bond activation was observed in all reactions, hydrogen elimination was observed as the prominent reaction for the alkenes (2-butene, isobutene, 1-pentene, and 2-pentene), alkynes (1-butyne, 2-butyne, and 1-pentyne), …

Characterization And Application Of Hybrid Nanostructures For Enhanced Biological Imaging Using Fluorescence Microscopy Techniques, William E. Martin

Theses and Dissertations--Chemistry

Fluorescence microscopy is a powerful tool for interpreting the structure and function of biomolecules, and their interactions with one another. Understanding fundamental biological mechanisms is important to the development of improved treatments for a variety of diseases. Fluorescent tags are used to track the motion and longevity of such events, with the ability to monitor several biomolecules at once. Currently, many of these studies are conducted using bulk measurements, or several biological events at the same time, because the added light from several emitters can more easily overcome the high fluorescence background inherent to biological systems. Although important in their …

Photoluminescence Mechanism And Applications Of Graphene Quantum Dots, Yiyang Liu

Theses and Dissertations--Chemistry

Graphene quantum dots (GQDs) are small pieces of graphene oxide whose physical dimensions are so confined (a few to a few tens nm) that they have a finite bandgap due to a quantum confinement effect. The finite bandgap of GQDs grants them pronounced absorption bands and a substantial photoluminescence. These optical properties are rarely observed in traditional carbon materials, since most of carbon materials are metallic with a near-zero bandgap and thus have broad absorption spectra with no photoluminescence. The unique optical properties of GQDs, along with GQDs’ inherited advantages from carbon material family (cheap, abundant, non-toxic), make GQDs an …

Semiconductor Photocatalysis: Mechanisms, Photocatalytic Performances And Lifetime Of Redox Carriers, Ruixin Zhou

Theses and Dissertations--Chemistry

Photocatalytic reactions mediated by semiconductors such as ZnS, TiO₂, ZnO, etc. can harvest solar energy into chemical bonds, a process with important prebiotic and environmental chemistry applications. The recycling of CO₂ into organic molecules (e.g., formate, methane, and methanol) facilitated by irradiated semiconductors such as colloidal ZnS nanoparticles has been demonstrated. ZnS can also drive prebiotic reactions from the reductive tricarboxylic acid (rTCA) cycle such as the reduction of fumarate to succinate. However, the mechanism of photoreduction by ZnS of the previous reaction has not been understood. Thus, this thesis reports the mechanisms for heterogeneous photocatalytic reductions …

Spectroscopic Characterization Of Lanthanum-Mediated Hydrocarbon Activation, Dilrukshi C. Hewage

Theses and Dissertations--Chemistry

Lanthanum (La)-promoted hydrocarbon activation reactions were carried out in a laser vaporization metal cluster beam source. Reaction products were identified by time-of-flight mass spectrometry, and the approximate ionization thresholds of La-hydrocarbon complexes were located with photoionization efficiency spectroscopy. The accurate ionization energies and vibrational frequencies of the La complexes were measured using mass analyzed threshold ionization (MATI) spectroscopy. Their molecular structures and electronic states were investigated by combing the MATI spectroscopic measurements with quantum chemical and Franck-Condon factor calculations.

In this dissertation, La-mediated C-H and C-C bond activation reactions were investigated for several small alkynes (acetylene, propyne) and alkenes (propene, …

Electron And Ion Spectroscopy Of Metal Hydrocarbon Complexes, Sudesh Kumari

Theses and Dissertations--Chemistry

Metal-hydrocarbon complexes were prepared in a laser-vaporization molecular beam source and studied by single-photon zero electron kinetic energy (ZEKE) and mass-analyzed threshold ionization (MATI) spectroscopy. The ionization energies and vibrational frequencies of the metal complexes were measured from the ZEKE and MATI spectra. Metal-ligand bonding and low-lying electronic states of the neutral and ionized complexes were analyzed by combining the spectroscopic measurements with quantum chemical calculations and spectral simulations.

In this dissertation, the metal complexes of mesitylene, aniline, cyclooctatetraene, benzene, ethene, and propene were studied. For each complex, different effects from metal coordination have been identified. Although metal-bis(mesitylene) sandwich complexes …

Structures And Electronic States Of Small Group 3 Metal Clusters, Lu Wu

Theses and Dissertations--Chemistry

Group 3 metal clusters are synthesized by laser vaporization in a pulsed cluster beam source and identified with laser ionization time-of-flight mass spectrometry. The adiabatic ionization energies and vibrational frequencies of these clusters are measured using mass-analyzed threshold ionization (MATI) spectroscopy. Their structures and electronic states are determined by combining the MATI spectra with quantum chemical calculations and spectral simulations. This dissertation focuses on the study of several small molecules, which include LaO₂, La₂, M₂O₂, M₃O₄, M₃C₂, and La₃C₂O, where …

Laser Spectroscopy Of Radicals Containing Group Iiia And Va Elements, Robert A. Grimminger

Theses and Dissertations--Chemistry

Radicals are interesting to study because of importance in so many processes such as semiconductor growth or stellar evolution. Laser induced fluorescence (LIF) and wavelength resolved emission spectra of jet cooled HPS, HAsO, AsD₂, H₂PS, and F₂BO have been measured using the pulsed discharge jet technique.

Several bands in the à ¹A′′ − X̃ ¹A′ transition of HPS were observed and assigned with the help of ab initio calculations. The ab initio geometries showed that HPS does not follow Walsh’s predictions for the angle change upon electronic excitation; Walsh predicts an increase …

Electrode And Electrolyte Additives For Lifetime Extension In Lithium-Ion Batteries, Kishore Anand Narayana

Theses and Dissertations--Chemistry

Lithium-ion batteries (LIBs) are the most commonly used type of rechargeable batteries with a global market estimated at $11 billion, which is predicted to grow to $60 billion by 2020. The global commercialization of Li-ion batteries is impeded by issues such as poor cycle life (5000 cycles achieved in some LIBs) in high energy and power density applications because of the rising internal resistance due to aging and safety concerns such as overcharge which ultimately leads to thermal runaway and explosions. A battery’s performance mainly depends on external factors such as electrode thickness and degree of compacting, and the type …

Structures And Reactions Of Biomolecules At Interfaces, Xiaoning Zhang

Theses and Dissertations--Chemistry

This dissertation serves to study a protein's conformation-function relationship since immobilized proteins often behave differently from their solution-state counterparts. Therefore, this study is important to the application of protein-based biodevices. Another aim of this dissertation is to explore a new approach to realize low voltage electrowetting without the help of oil bath. Utilizing this approach, a protein micro-separation was realized. Additionally, the interfacial properties of ionic liquid (IL) solid-like layer, which played a key role in electrowetting, was studied for further developments of IL-based applications.

Atomic Force Microscopy (AFM) was utilized in the study and played multiple roles in this …

Studies Of Organic Compounds Spreading Over High Energy Surfaces, Lingbo Lu

Theses and Dissertations--Chemistry

Spreading plays an important role in coating, lubrication, printing and etc. During the spreading process, a liquid thin film forms prior to the expansion of a liquid drop. This thin film is called a precursor film. It not only changes the spreading mechanism, but impacts the wettability of a liquid. Early studies on the precursor films showed the films were stacked in a terraced structure, and the radius of each layer of the films was proportional to the square root of time. Optical techniques such as ellipsometry, X-ray diffraction and X-ray reflectivity solved the conformations of liquid molecules at the …

Efficient Electrochemical Functionalization Of Carbon Nanotubes And Carbon Nanotube Membranes For Energy, Drug Delivery And Potential Catalysis Applications, Xin Zhan

Theses and Dissertations--Chemistry

Electrochemical diazonium grafting offers versatile functionalization of chemically inert graphite under mild condition, which is particularly suitable for CNT composite modification. Tetrafluorinated carboxylphenyl diazonium grafting provides the most controllable functionalization chemistry allowing near monolayer levels of functionality on carbon nanotubes. The functional density was successfully quantified by anion selective dye-assay and X-ray photoelectron spectroscopy (XPS) of thiol-Au self-assembled monolayers (SAM) as a calibration reference. This technique enables monolayer functionality at the tips of carbon nanotube membranes for biomimetic pumps and valves as well as thin conductive layers for CNT-based high area electrochemical support electrodes.

Double-walled carbon nanotube (DWCNT) membranes were …

Spectroscopic Detection And Characterization Of Jet-Cooled Transient Molecules, Mohammed Gharaibeh

Theses and Dissertations--Chemistry

Transient molecules are of great importance due to their critical role as intermediates in the semiconductor industry, in upper atmosphere reactions, and in astrochemistry. In the present work, reactive intermediates were produced in the laboratory by applying an electric discharge through a suitable precursor gas mixture and studied by means of their laser-induced fluorescence and emission spectra.

The band systems of and have been studied in detail. The energy levels of both isotopologues were fitted with a Renner-Teller model, and the isotope relations have been used to test the validity of the derived parameters.

The A²Π_u - …