Chemistry & Biochemistry Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2752
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Item UNVEILING THE SELF-ASSEMBLY OF POLYMER-GRAFTED NANOPARTICLES IN SELECTIVE SOLVENTS(2023) Lamar, Chelsey; Nie, Zhihong; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The self-assembly of inorganic nanoparticles (NPs) has garnered considerable attention due to the potential for fabricating functional structures with unique collective properties. In recent years, polymers have emerged as valuable candidates in assisting the organization of NPs into complex architectures with multiple capabilities. Researchers have shown that polymer-grafted nanoparticles (PGNPs) facilitate the use of advanced nanostructures with tailored properties in biomedical applications. Although, continued exploration of the rational design and tailoring of PGNP assemblies is needed to expand our understanding before we can fully realize the potential of these structures in desired applications. My dissertation aims to investigate the fundamental aspects and elucidate the underlying mechanisms in the self-assembly of PGNPs for modern biomedical applications. A facile and versatile solution-based strategy was utilized to explore the individual self-assembly of PGNPs with anisotropic NPs and the co-assembly of binary PGNPs with distinct sizes. We focused on designing, characterizing, and exploring the optical properties of hierarchical assembly structures produced from inorganic NPs tethered with amphiphilic block copolymers (BCPs). Individual PNGPs with anisotropic NPs and binary mixtures of small and large PGNPs produce vesicle structures with well-defined packing arrangements. My work shows how key parameters, including polymer chain length, nanoparticle size, and concentration, influence the self-assembly behavior and the formation of vesicles in each system. Through a combination of experimental observations and theoretical considerations, I highlight the significance of polymer shell shape in dictating the self-assembly behavior of individual anisotropic PGNPs. Moreover, I demonstrate that elevated temperatures impacted the stability and optical responses of the vesicle structures. In co-assembly studies, my work describes the macroscopic segregation of PGNPs with different sizes in the vesicular membrane, which is attributed to the conformation entropy gain of the grafted copolymer ligands. This research will provide valuable insights into the self-assembly behavior and fundamental design of PGNP structures relevant to biomedical applications.Item Fluorescent Carbon Nanotubes as Molecular Sensors and Color-Center Hosts(2022) Qu, Haoran; Wang, YuHuang; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis demonstrates the application of single-walled carbon nanotubes (SWCNTs) as single-digit nanopores for molecular sieving and addresses a fundamental challenge pertaining to controlled synthesis of organic color-centers (OCCs) on the sp2 carbon lattice of SWCNTs. First, I describe a hyperspectral single-defect photoluminescence imager system that provides both hyperspectral imaging and super-resolution capabilities in the shortwave infrared. Second, I aim to understand the relationship between nanotube photoluminescence and encapsulated molecules. Using carbon nanotubes with sub-1 nm pores, I demonstrate molecular sieving of n-hexane from cyclohexane, which are nearly identical in size. Furthermore, I discovered a light irradiation method to drive structural transformation of OCCs which allow us to narrow the spectral distribution of defect emissions by 26%. Finally, I show that [2+2] cycloaddition can efficiently create OCCs. Remarkably, this novel defect chemistry reduces the number of OCC bonding configurations from six, which are commonly observed with monovalent defect chemistries, to just three. This work may have broad implications to the potential applications of SWCNTs and OCCs in chemical sensing, bioimaging, and quantum information science.Item Hybrid plasmonic tubular nanostructures: synthesis, optical and photoelectrocatalytic property(2022) Zhang, Qian; Lee, Sang Bok; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Utilizing sustainable and clean solar energy in the visible-NIR range to drive chemical transformation has been a key resolution to solve the energy crisis. Recently, rational design of photocatalysts that conjugate plasmonic nanostructures with catalytic metal nanostructures has attracted particular research interests. This dissertation describes the design principles of plasmonic-catalytic hybrid tubular nanostructures and investigates their application in photoelectrocatalytic reactions.First, we introduced the mechanism of plasmon-mediated catalysis and current research of plasmonic photocatalysts. Specifically, managing the energy flow from the plasmonic entity to the catalytic entity is the crucial part for customizable design of photoelectrocatalysts. We also summarized the design principles of general electrocatalysts and synthesis of hollow nanostructures. Second, we reported a facile but highly reproducible synthetic strategy to fabricate catalytic Pt hollow nanotubes (NTs). Scalable fabrication of ultrathin Pt NTs can be achieved through simple mediation of the concentration of the surfactant employed in the reaction. Third, we reported a template-directed synthesis of PtAu NTs with tunable localized surface plasmon resonance (LSPR) bands in the visible-near infrared region (NIR). The geometric dependent LSPR band shift was systematically studied based off the spectra from both experiment and finite-difference time-domain (FDTD) simulations. It was found that the PtAu NTs exhibited the LSPR characters of both rodlike and hollow nanostructures. Finally, we investigated the photoelectrocatalytic performance of the PtAu NTs under visible-NIR light irradiation. The optimized photocatalytic activity of the PtAu NTs towards the electrooxidation of methanol was achieved by maximizing their LSPR absorption cross sections at longer wavelengths in the visible-NIR region. Meanwhile, combining the superior intrinsic electrocatalytic performance of PtAu NTs towards methanol oxidation, we expected the bimetallic PtAu tubular nanostructure could effectively convert visible light energy to drive the electrochemical transformation.Item SYNTHESIS AND POLYMER-MEDIATED REGIOSELECTIVE SELF-ASSEMBLY OF SHAPED PLASMONIC NANOPARTICLES(2021) Lin, Xiaoying; Fourkas, John T; Nie, Zhihong; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Plasmonic nanoparticles with collective excitations of the conduction-band electrons have many potential applications in surfaceenhanced spectroscopies, photocatalysis, photovoltaics, and biomedicine. The plasmonic properties are highly tunable via the size, shape, chemical composition, and surrounding media of individual nanoparticles, as well as by the interactions with other nanoparticles in close proximity. Fabricating plasmonic nanostructures with precisely controlled size, shape, and interparticle distance is critical for harnessing desirable properties. Although top-down lithographic techniques are widely used for fabricating shaped plasmonic nanoparticles and ensembles, the products are limited to 2D planar structures and the cost can be prohibitive. As low-cost and versatile alternatives, colloidal synthesis and self-assembly have been explored to fabricate complex plasmonic nanostructures.In this dissertation, wet-chemistry synthetic and self-assembly approaches are explored for fabricating well-defined plasmonic nanostructures with high structural complexity. Chapter 2 describes a facile synthetic method for circular and triangular gold nanorings with tunable diameters, ring thicknesses, surface roughness, and hence the plasmonic response. The gold nanorings with rough surface show 100-fold higher enhancement factor than solid gold nanoparticles as substrate for surface-enhanced Raman spectroscopy. In chapter 3, we demonstrate regioselective bonding between nanospheres and nanoplates originating from the steric hindrance of polymeric ligand brushes and the anisotropy of nanoparticles. The regioselectivity enables a self-assembly system with precise control over the relative orientation of Au nanospheres on Ag nanoplates and the stoichiometry of reactive groups of copolymeric ligands dictates the number of nanoparticles in one nanocluster. The yield of each assembly was ~70% without further purification. Optical study reveals that different bonding modes affect the plasmonic coupling of assembled structures. In chapter 4, the regioselective bonding is applied to fabricate complex plasmonic nanocluster, nanoflowers and nanobuds, with distinct bonding modes. Compared with nanobuds, nanoflowers with the same number of petals show stronger electric field enhancement and further localized surface plasmon resonance peak shifts. The synthetic and self-assembly methods demonstrated in this dissertation have great potentials and versatility in designing not only plasmonic nanoclusters, but also other inorganic nanoparticle-based functional structures with high complexity.Item ATOMICALLY PRECISE FABRICATION AND CHARACTERIZATION OF DONOR-BASED QUANTUM DEVICES IN SILICON(2019) Wang, Xiqiao; Silver, Richard M; Appelbaum, Ian; Chemical Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Atomically precise donor-based quantum devices in silicon are a promising candidate for scalable solid-state quantum computing and analog quantum simulation. This thesis demonstrates success in fabricating state-of-the-art silicon-phosphorus (Si:P) quantum devices with atomic precision. We present critical advances towards fabricating high-fidelity qubit circuitry for scalable quantum information processing that demands unprecedented precision and reproducibility to control and characterize precisely placed donors, electrodes, and the quantum interactions between them. We present an optimized atomically precise fabrication scheme with improved process control strategies to encapsulate scanning tunneling microscope (STM)-patterned devices and technological advancements in device registration and electrical contact formation that drastically increase the yield of atomic-precision fabrication. We present an atomic-scale characterization of monolayer step edges on Si (100) surfaces using spatially resolved scanning tunneling spectroscopy and quantitatively determine the impact of step edge density of states on the local electrostatic environment. Utilizing local band bending corrections, we report a significant band gap narrowing behavior along rebonded SB step edges on a degenerately boron-doped Si substrate. We quantify and control atomic-scale dopant movement and electrical activation in silicon phosphorus (Si:P) monolayers using room-temperature grown locking layers (LL), sputter profiling simulation, and magnetotransport measurements. We explore the impact of LL growth conditions on dopant confinement and show that the dopant segregation length can be suppressed below one Si lattice constant while maintaining good epitaxy. We demonstrate weak-localization measurement as a high-resolution, high-throughput, and non-destructive method in determining the conducting layer thickness in the sub-nanometer thickness regime. Finally, we present atomic-scale control of tunnel coupling using STM-patterned Si:P single electron transistors (SET). We demonstrate the exponential scaling of tunnel coupling down to the atomic limit by utilizing the Si (100) 2×1 surface reconstruction lattice as a natural ruler with atomic-accuracy and varying the number of lattices counts in the tunnel gaps. We analyze resonant tunneling spectroscopy through atomically precise tunnel gaps as we scale the SET islands down to the few-donor quantum dot regime. Finally, by combining single/few-donor quantum dots with atomically defined single electron transistors as charge sensors, we demonstrate single electron charge sensing in few-donor quantum dots and characterize the tunnel coupling between few-donor quantum dots and precision-aligned single electron charge sensors.Item Dielectric studies of Liquid Crystal Nanocomposites and Nanomaterial systems.(2016) Kempaiah, Ravindra; Nie, Zhihong; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Liquid crystals (LCs) have revolutionized the display and communication technologies. Doping of LCs with inorganic nanoparticles such as carbon nanotubes, gold nanoparticles and ferroelectric nanoparticles have garnered the interest of research community as they aid in improving the electro-optic performance. In this thesis, we examine a hybrid nanocomposite comprising of 5CB liquid crystal and block copolymer functionalized barium titanate ferroelectric nanoparticles. This hybrid system exhibits a giant soft-memory effect. Here, spontaneous polarization of ferroelectric nanoparticles couples synergistically with the radially aligned BCP chains to create nanoscopic domains that can be rotated electromechanically and locked in space even after the removal of the applied electric field. The resulting non-volatile memory is several times larger than the non-functionalized sample and provides an insight into the role of non-covalent polymer functionalization. We also present the latest results from the dielectric and spectroscopic study of field assisted alignment of gold nanorods.Item Bimetallic Nanoparticles for Advanced Energy Conversion Technologies(2015) Sims, Christopher; Eichhorn, Bryan W; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The increased demand for a more sustainable energy infrastructure has spurred the development of innovative energy conversion processes and devices, such as the proton exchange membrane fuel cell (PEMFC). PEMFCs are highly regarded as a clean alternative energy technology for various applications, such as motor vehicles or power generators. Factors limiting their commercial viability include the poisoning of the hydrogen oxidation reaction (HOR) electrocatalyst at the anode by carbon monoxide (CO), an impurity in the H2 fuel feedstocks derived from hydrocarbons, and the high expense and inefficiency of the oxygen reduction reaction (ORR) electrocatalyst at the cathode. The research described in this dissertation entails the synthesis and characterization of new bimetallic nanoparticle (NP) catalysts with controlled sizes, compositions, and architectures. By varying the NPs' compositions, structures, and electronic environments, we aimed to elucidate the physical and chemical relationships that govern their ability to catalyze chemical reactions pertinent to PEMFC operation. The ongoing research and development of these NP-based catalytic systems is essential to realizing the viability of this energy conversion technology. We describe the development of a simple method for synthesizing monometallic and bimetallic NPs supported on various reduced graphene oxide (rGO) supports. Electrochemical studies illustrate how the chemical nature of the rGO support impacts the catalytic behavior of the NP catalysts through unique metal-support interactions that differ depending on the elemental composition of the NP substrate. In another study, we present the synthesis and characterization of CoxPty NPs with alloy and intermetallic architectures and describe how their inherent characteristics impact their catalytic activities for electrochemical reactions. CoxPty NPs with alloy architectures were found to have improved CO tolerance compared to their intermetallic counterparts, while the performance of the CoxPty NPs for ORR catalysis was shown to be highly dependent on the NPs' crystal structure. Finally, we present the synthesis and characterization of various bimetallic core-shell NPs. Preliminary data for CO oxidation and PrOx catalysis demonstrated how subsurface metals modify the electronic structure of Ni and enhances its catalytic performance for CO oxidation and the PrOx reaction.Item Earth Abundant Bimetallic Nanoparticles for Heterogeneous Catalysis(2014) Senn Jr, Jonathan Fitzgerald; Eichhorn, Bryan; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Polymer exchange membrane fuel cells have the potential to replace current fossil fuel-based technologies in terms of emissions and efficiency, but CO contamination of H2 fuel, which is derived from steam methane reforming, leads to system inefficiency or failure. Solutions currently under development are bimetallic nanoparticles comprised of earth-abundant metals in different architectures to reduce the concentration of CO by PROX during fuel cell operation. Chapter One introduces the Pt-Sn and Co-Ni bimetallic nanoparticle systems, and the intermetallic and core-shell architectures of interest for catalytic evaluation. Application, theory, and studies associated with the efficacy of these nanoparticles are briefly reviewed. Chapter Two describes the concepts of the synthetic and characterization methods used in this work. Chapter Three presents the synthetic, characterization, and catalytic findings of this research. Pt, PtSn, PtSn2, and Pt3Sn nanoparticles have been synthesized and supported on γ-Al2O3. Pt3Sn was shown to be an effective PROX catalyst in various gas feed conditions, such as the gas mixture incorporating 0.1% CO, which displayed a light-off temperatures of ~95°C. Co and Ni monometallic and CoNi bimetallic nanoparticles have been synthesized and characterized, ultimately leading to the development of target Co@Ni core-shell nanoparticles. Proposed studies of catalytic properties of these nanoparticles in preferential oxidation of CO (PROX) reactions will further elucidate the effects of different crystallographic phases, nanoparticle-support interactions, and architecture on catalysis, and provide fundamental understanding of catalysis with nanoparticles composed of earth abundant metals in different architectures.Item Understanding and Tuning Nanostructured Materials for Chemical Energy Conversion(2014) Jian, Guoqiang; Zachariah, Michael R; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The conversion of energy that employs chemical reaction is termed chemical energy conversion. In my dissertation, I have focused on chemical energy conversion systems involving energetic materials and lithium ion batteries, where performance is strongly dependent on the properties of materials and their architecture. The objective of this study is to enhance our understanding and tuning of nanostructured materials that might find application toward energetic materials and electrode materials in lithium ion batteries. Rapid heating diagnostics tools, i.e. temperature-jump techniques, have been used to study the ignition of aluminum nanoparticles, nanothermite reaction mechanism and metal oxides nanoparticles decomposition under rapid heating conditions (~105-106 K/s). Time-resolved mass spectra results support the hypothesis that Al containing species diffuse outwards through the oxide shell. Low effective activation energies were found for metal oxides nanoparticles decomposition at high heating rates, implying the mass transfer control at high heating rates. The role of oxygen release from oxidizer in nanothermite reactions have been examined for several different systems, including some using microsized oxidizer (i.e., nano-Al/micro-I2O5). In particular, for periodate based nanothermites, direct evidence from high heating rate SEM and mass spectrometry results support that direct gas phase oxygen release from oxidizer decomposition is critical in its ignition and combustion. Efforts have also been made to synthesize nanostructured materials for nanoenergetic materials and lithium ion batteries applications. Hollow CuO spheres were synthesized by aerosol spray pyrolysis, employing a gas blowing mechanism for the formation of hollow structure during aerosol synthesis. The materials synthesized as oxidizers in nanothermite demonstrated superior performance, and of particular note, periodate salts based nanothermite demonstrated the best gas generating performance for nanothermite materials. Energetic composite nanofibrous mats (NC/Al-CuO, NC/Al-Fe2O3, and NC/Al-Bi2O3) were also prepared by an electrospinning method and evaluated for their combustion performance. Aerosol spray pyrolysis was employed to produce carbon coated CuO hollow spheres, Mn3O4 hollow spheres, and Fe2O3 mesoporous spheres. These hollow/mesoporous spheres demonstrated superior electrochemical performance when used as anode materials in lithium ion batteries. The effects of the amorphous and crystal structures on the electrochemical performance and the structure evolution during electrochemical tests were also investigated.Item CATANIONIC SURFACTANT VESICLES: TECHNOLOGY FOR VACCINE DEVELOPMENT AND TARGETED DRUG DELIVERY APPLICATIONS(2013) Stocker, Lenea Hope; DeShong, Philip; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Catanionic surfactant vesicles have gained attention due to their structural similarities to liposomes and their robust properties in biological media. Catanionic vesicles are formed from oppositely charged surfactants and can be exploited for applications in vaccine production and drug delivery. The focus of my research has been on the preparation, characterization, and application of functionalized catanionic surfactant vesicles. Chapter 2 describes the preparation and characterization of catanionic vesicles containing sodium dodecylbenzenesulfonate (SDBS) and cetyltrimethylammonium tosylate (CTAT). Vesicle solutions were determined to be stable for greater than 6 months, formed vesicles with two populations of 80 and 160 nm, and had a membrane surface charge similar to human cells, -56 mV. Furthermore, vesicles were stable between a pH of 2 and 12, in saline solutions up to 0.6 M NaCl, and after autoclaving. Next, I report the loading of various molecules into the vesicle leaflet and the characterization of the resulting functionalized systems. Hydrophobic molecules were readily incorporated into the hydrophobic region of the leaflet. Lipid conjugates of hydrophilic molecules were anchored in the vesicle bilayer. Chapters 3 and 4 report the loading of biological materials (i.e. liposaccharides and proteins) into catanionic vesicles for the development of bacterial vaccines. Initial studies, discussed in Chapter 3, pertain to the loading of the pure components lipooligosaccharide (LOS) and C12 -Pan DR helper T cell epitope (PADRE) conjugate into catanionic vesicles. A single dose of these vesicles generated a large IgG antibody titer in mice. Next, in Chapter 4, we focus on the extraction of cellular membrane components from cells for their direct incorporation into catanionic vesicles. Vesicles were prepared by adding surfactants in the presence of Neisseria gonorrhoeae cells. Vesicle extracts contained pathogen-derived LOS F62ΔlgtD and a subset of proteins from the outer membrane of the bacterium, including porin and OPA. Lastly, Chapter 5 describes catanionic vesicles in drug delivery. Vesicles were loaded with 88 μg/mL of doxorubicin and shown to retain the drug over 15 days. Doxorubicin loaded into catanionic vesicles were shown to be less toxic as compared to the free drug, IC 50 = 51 μg/mL and 0.16 μg/mL, respectively.