Chemistry & Biochemistry Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2752
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Item Nature-Inspired Polymeric Materials: Unveiling Unique Responsive Properties(2023) Rath, Medha; Woehl, Taylor J.; Raghavan, Srinivasa R.; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In nature, biological systems are able to respond autonomously to environmental cues. Drawing inspiration from nature, scientists have been creating materials that change their appearance, shape, or properties (e.g., optical or mechanical) in response to various stimuli. This work is our contribution to the field - we have designed a range of nature-inspired polymeric materials that reconfigure their properties in response to either physical cues (e.g., temperature) or chemicals in the external medium. In our initial study, our point of inspiration is the natural pearl, which displays a bright sheen (called ‘pearlescence’) due to light reflection from plate-like particles. We show, for the first time, that pearlescence can be reversibly induced in soft capsules that contain no plate-like particles. Our millimeter-sized capsules have an outer shell (~ 500 µm thick) of N-isopropylacrylamide (NIPA) gel, which shrinks above its lower critical solution temperature (LCST) of ~ 32°C. When a transparent capsule is heated above this LCST, it turns pearlescent, and the transparent state is recovered upon cooling. Specular reflectance measurements confirm that the pearlescence of the capsules is comparable to that of natural pearls. We attribute the pearlescence to light reflection from nanoscale domains in the shrunken NIPA shell above the LCST. Next, we draw inspiration from the skin of chameleons - the brilliant colors of the skin are due to ordered arrays (photonic crystals) of particles within the skin cells. To mimic this structure, we first create ‘photonic capsules’ with silica nanoparticles (NPs) in their liquid cores. When the capsules are placed in a polymer solution, the shell is impermeable to the polymer chains but is permeable to water. The resulting osmotic gradient induces the silica NPs to form close-packed arrays, i.e., photonic crystals, which deposit on the inner wall of the capsule. The capsules thereby show brilliant colors (iridescence), with the exact color depending on the NP size. We then further use these capsules as building blocks and fuse them together to form a free-standing sheet. The sheet is thus analogous to a tissue, with the capsules analogous to the constituent cells. We are thereby able to create a sheet of colored capsules, resembling the chameleon skin. Lastly, we take a step towards creating an ‘artificial muscle’. The muscles in our body are nature’s ideal machines as they can expand and contract at will. To mimic this ability, materials that change their size autonomously are of interest. With this goal in mind, we start with an anionic hydrogel with microscale pores - the gel expands by 300% when placed in water. When a carbodiimide is added to the water, it converts the carboxylates on the gel strands to anhydrides, and the loss of charge makes the gel shrink by 50%. The anhydrides are metastable, however, and hydrolyze over time - thereby, the charge on the chains is restored and the gel expands back to its initial size. A cycle of gel expansion and contraction is completed in ~ 40 min, which is ~ 10x faster than any previous soft autonomous material. The rapid response moves our gels closer to the timescales required for use in practical actuators or soft robots.Item Defect Engineering of Supported Metal Catalysts for Selective Hydrogenation(2022) Zhang, Yuan; Liu, Dongxia; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Supported metal catalysts have been used extensively in industry. To construct supported metal catalysts with low cost and high catalytic performance, high dispersion of metal on the support material is greatly favored in recent years. With the downsizing of metal active phase, new challenges in catalyst synthesis and characterization have emerged. The highly dispersed metal active phase is prone to aggregate to decrease surface free energy, which requires innovative synthesis strategy to stabilize the metal species on support. High metal dispersion also created more interfacial sites and bonds between metal and support, therefore the metal-support interaction has more significant effects on the catalytic properties of high dispersion catalysts. Defect engineering has attracted much attention due to its ability to help stabilizing metal species and tune the metal-support interaction.This dissertation focuses on utilizing defect engineering to develop catalysts with high activity and selectivity in hydrogenation reaction. Harsh pH condition was applied in wetness impregnation process to generate cavity sites on TiO2 support surface, which resulted in stronger metal-support interaction between Pt and TiO2. The catalyst synthesized under harsh condition showed higher hydrogenation activity towards -NO2 group. Laser engraving was used as another defect engineering technique to create defects on TiO2 support. The laser engraved support showed distinct electronic and redox properties, which enhanced the electronic metal-support interaction of Pt and TiO2 support. The Pt/TiO2-LE catalyst showed superior activity and selectivity in the hydrogenation of 3-nitrostyrene and furfural alcohol. In addition, an effective method to probe the metal dispersion of Pt by styrene hydrogenation reaction kinetics was developed. This method has the potential to be applied to other catalysts systems and could be used to study the metal-support interaction in catalysts.Item UNDERSTANDING AND TAILORING THE REACTIVE CHARACTERISTICS OF NANOENERGETIC COMPOSITES VIA STRUCTURAL AND CHEMICAL MODIFICATIONS(2022) XU, FEIYU; Zachariah, Michael R; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Nanoenergetic composites are nanostructured fuel and oxidizer mixtures that store a large amount of chemical energy and release it, typically in the form of heat, upon ignition. They are promising candidates for energy intensive applications such as propellants and pyrotechnics, due to their high energy density. The overall reaction kinetics of the heterogenous nanoenergetic system is controlled by mass transfer. The use of nanoparticles is to reduce diffusion length and thus increase energy release rate. The objective of the proposed research is to understand how intrinsic properties of fuel and oxidizer affect the reaction of nanoenergetic composites, and to develop novel, multifunctional nanoenergetic materials with tunable ignition threshold and energy release rate. Experiments were conducted utilizing primarily a time resolved Temperature-Jump time-of-flight mass spectrometer (T-Jump TOFMS) to analyze gas phase reaction intermediatespecies and products at a high heating rate (~105 K/s), along with a combustion cell for reactivity evaluation. New fuels including hydrogenated amorphous silicon, and oxidizers including oxygen deficient Co3O4-x and ferroelectric Bi2WO6 were investigated. The role of surface chemistry in the energetic characteristics of silicon nanoparticles was investigated, leading to the uncovering of a new reaction mechanism. Modulating the initiation temperature of aluminothermic reaction via defect engineered metal oxide was demonstrated. A study of piezoelectric oxidizers reveals the superior reactivity of a complex metal oxide. Moreover, tuning the energy release rate of I2O5 based biocidal nanoenergetic composites via a ternary system was studied. These results indicate that by modifying the chemistry or structure of fuels and oxidizers, the combustion characteristics of nanoenergetic composites can be tailored.Item LIGHT CONTROL OF CHEMICAL SYSTEMS: PHOTOCHEMICAL ELECTRON TRANSFER METHODS FOR RELEASING CALCIUM IONS AND THE PHOTOISOMERIZATION OF ALKENES TO MODULATE RHEOLOGICAL CHANGES.(2021) Heymann Loor, Romina R; Falvey, Daniel E; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Our research combines organic photochemistry with the engineering principles of rheology through the study of photorheological fluids (PR). The two photochemical systems researched show changes in the rheological properties brought about by the addition of light. The investigated systems are the photoisomerization of cinnamic acid derivatives in the surfactant, Cetyltrimethylammonium bromide (CTAB), and calcium release through degradation ethylenediaminetetraacetic acid (EDTA) caused by an electron transfer mechanism. The CTAB system shows how a change in molecular conformation can cause significant changes in the bulk property of a solution. The calcium EDTA system employs targeted electron transfer to cause calcium release, which gels the biopolymer alginate with inexpensive, readily available materials. Chapter 2 details how the orientational binding, intermolecular interactions, and molecular geometry of cinnamic acid derivatives contribute to the rheological changes in CTAB. 1H NMR titration studies in CTAB identified binding patterns of the additives in CTAB. From those studies orientational binding models were developed for trans-ortho-methoxycinnamic acid (tOMCA), cis-ortho-methoxycinnamic acid (cOMCA), meta-methoxycinnamic acid (mMCA), para-methoxycinnamic (pMCA), ortho-hydroxycinnamic acid (oCoum), meta-hydroxycinnamic acid (mCoum), and para-hydroxycinnamic acid (pCoum). 1H-1H 2D NOESY spectra identified through space intermolecular interactions occurring within the micelle. Preliminary data into possible π-anion interaction between tOMCA molecules within the micelle is presented. Photolysis confirmed the creation of cis isomers for all additives but also identified coumarin by-products for oCoum. B3LYP calculations indicated out-of-plane geometry for all the cis isomers and possible intramolecular hydrogen bonding of oCoum. Finally, a model of binding interactions that lead to changes in the packing parameter of the surfactant and, therefore, a change into wormlike micelles for tOMCA versus cOMCA is introduced. In chapters three and four, we investigated calcium release using sensitizers that promote photoinduced electron transfer. Anthraquinones derivatives were shown in Chapter 3 to release calcium in stoichiometry amounts with UV light irradiation. In Chapter 4, flavins produced 1000-fold calcium release to sensitizer concentration in the visible light spectrum. In both chapters, there are detailed calcium release studies, degradation studies, and alginate experiments. We present calcium release studies at acidic and neutral pH, quantum yields, degradation of EDTA, sensitizer reoxidation studies, sensitizer degradation data, fluorescence, and transient spectra. While enough calcium was released to produce alginate gels, none were made in vitro at neutral and acidic pH.Item RAPID HEATING AND CHEMICAL SPECIATION CHARACTERIZATION FOR COMBUSTION PERFORMANCE ANALYSIS OF METALLIZED, NANOSCALE THERMITES AND PVDF BOUND SOLID PROPELLANT COMPOSITIONS(2021) Rehwoldt, Miles Christian; Rodriguez, Efrain; Zachariah, Michael R; Chemical Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Energetic materials research focuses on performance analysis of cost-effective solid materials which safely, precisely, and efficiently transitions stored chemical potential energy to kinetic energy at a rate throttled through chemical or architectural means. Heterogenous compositions of metal fuels and solid materials with a high storage capacity of condensed oxidizing elements, such as oxygen and/or fluorine, is a class of energetic material of interest given its relatively high reaction enthalpies and adiabatic flame temperatures. In the wake of the earliest instances of metal fuels being used as a high energy additive during World War II, characterizing the reaction mechanisms of micron and nanoparticle aluminum fuels with various oxidizer sources has been a primary subject of research within the solid energetics community. The advent of nanotechnologies within the past two decades brought with it the promise of a prospective revolution within the energetics community to expand the utility and characterization of metallized energetic materials in solid propellants and pyrotechnics. Significant prior research has mapped reactivity advantages, as well as the many short comings of aluminum-based nanoscale energetic formulations. Examples of short comings include difficulties of materials processing, relative increase in native oxide shell thickness, and particle aggregate sintering before primary reaction. The less than flaw-less promises of nanoscale aluminum fuels have thus become the impetus for the development of novel architectural solutions and material formulations to eliminate drawbacks of nanomaterial energetics while maintaining and improving the benefits. This dissertation focuses on further understanding reaction mechanisms and overall combustion behavior of nanoscale solid energetic composite materials and their potential future applications. My research branches out from the heavy research involved in binary, aluminum centric systems by developing generalized intuition of reaction and combustion behaviors through modeling efforts and coupling time-of-flight mass spectrometry to rapid heating techniques and novel modes of product sampling. The studies emphasize reaction mechanisms and microwave sensitivities of under-utilized compositions using metal fuels such as titanium, generalize the understanding of the interaction of fluoropolymer binders with metal fuels and oxidizer particles, and characterize how multi-scale architectural structure-function relations of materials effect ignition properties and energy release rates.Item UNDERSTANDING THE SURFACE CHEMISTRY OF GAS PHASE ORGANOPHOSPHORUS CHEMICAL WARFARE AGENTS WITH SORBENT MATERIALS(2019) Holdren, Scott; Zachariah, Michael R.; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Chemical warfare agents (CWAs) pose a serious threat to civilians and warfighters due to their high toxicity and usage in recent attacks. Although existing filtration media (ASZM-TEDA) used in gas mask devices absorbs and decomposes a wide spectrum of CWAs, the filtration performance of this material can be compromised in the battlefield due to poorly understood mechanisms. The high toxicity of CWAs remains a barrier for most research institutions to study these compounds experimentally which hinders the search for improved filtration materials. To overcome this issue, studies are performed using relatively benign simulant compounds that have similar adsorption and decomposition properties as toxic CWAs. In this work, a report of experimental findings will be presented regarding how dimethyl methylphosphonate (DMMP), an organophosphorus CWA simulant, will adsorb and decompose on components that makeup ASZM-TEDA. The work presented in this dissertation deconstructs the components that makeup ASZM-TEDA in order to identify the role of specific metal oxides and the carbon support. This approach was facilitated using different analytical techniques including TGA, FTIR spectroscopy, and DFT modeling to gain a molecular understanding of how DMMP interacts with porous carbon (Chapter 3) and metal oxide nanoparticles/surfaces (Chapters 4 and 5). Lastly, a new method is described (Chapter 6) that overcomes many of the difficulties encountered in conventional measurements that monitor gas phase DMMP adsorption/desorption processes on sorbent materials. This method can be used to obtain reliable quantitative measurements and parameters (e.g. adsorption capacities, ∆Hads, and kads) of low vapor pressure adsorbate/sorbent systems making it particularly useful for CWAs/CWA simulants and new filtration materials (e.g. DMMP and porous carbon).Item EXPLORING THE RELATIONSHIPS BETWEEN FUEL AND OXIDIZER REACTION OF BIOCIDAL ENERGETIC MATERIALS(2019) Wu, Tao; Zachariah, Michael R.; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Energetic materials are defined as a class of material with extremely high amount of stored chemical energy that can be released when ignited, along with intensive light emission and shock generation. Developing new energetic materials with high efficiency neutralization of biological warfare agents has gained increased attention due to the increased threat of bioterrorism. The objective of this dissertation is to develop new energetic materials with biocidal capabilities and apply them in various nanothermite systems to explore the relationships between fuel and oxidizer reactions. Aerosol techniques offer a convenient route and potentially direct route for preparation of small particles with high purity, and is a method proven to be amenable and economical to scale-up. Here I demonstrate the synthesis of various iodine oxides/iodic acids microparticles by a direct one-step aerosol method from iodic acid. A previously misidentified phase of I4O9 hydrate is in fact a new polymorph of HIO3 which crystalizes in the orthorhombic space group P212121. Various iodine oxides/iodic acids, including I2O5, HI3O8 and HIO3, were employed as oxidizers in thermite systems. Their decomposition behaviors were studied using a home-made time resolved temperature-jump/time-of-flight mass spectrometer (T-Jump/TOFMS). In addition, nano-aluminum (nAl), nano-tantalum and carbon black were adopted as the fuel or additive in order to fully understand how iodine containing oxidizers react with the fuel during ignition. The ignition and reaction process of those thermites were characterized with T-Jump/TOFMS. Carbon black was found to be able to lower both initiation and iodine release temperatures compared to those of Al/iodine oxides and Ta/iodine oxides thermites. Their combustion properties were evaluated in a constant-volume combustion cell and results show that nAl/a-HI3O8 has the highest pressurization rate and peak pressure and shortest burn time. However, an ignition delay was always present in their pressure profiles while combusting. To shorten or eliminate this ignition delay, a secondary oxidizer CuO is incorporated into Al/I2O5 system and four different Al/I2O5/CuO thermites by varying the mass ratio between two oxidizers are prepared and studied in a constant volume combustion cell. Significant enhancement is observed for all four thermites and their peak pressures and pressurization rates are much higher than that of Al/I2O5 or Al/CuO. Two other oxidizers also demonstrate similar effects as to CuO on promoting the combustion performance of Al/I2O5. A novel oxidizer AgFeO2 particles was prepared via a wet-chemistry method and evaluated as an oxidizer in aluminum-based thermite system. Its structure, morphologies and thermal behavior were investigated using X-ray diffraction, scanning electron microscopy, TGA/DSC, and T-Jump/TOFMS. The results indicate the decomposition pathways of AgFeO2 vary with heating rates from a two-step at low heating rate to a single step at high heating rate. Ignition of Al/AgFeO2 at a temperature just above the oxygen release temperature and is very similar to Al/CuO. However, with a pressurization rate three times of Al/CuO, Al/AgFeO2 yields a comparable result to Al/hollow-CuO or Al/KClO4/CuO, with a simpler preparation method. T-Jump/TOFMS was used to study the ignition and decomposition of boron-based thermites. The ignition behaviors of bare boron nanopowders and boron-based nanothermites at various gaseous oxygen pressure were investigated using the T-Jump method. High-heating rate transmission electron microscopy studies were performed on both B/CuO and B/Bi2O3 nanothermites to evaluate the ignition process. I propose a co-sintering effect between B2O3 and the oxidizer play an important role in the ignition process of boron-based nanothermites.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 SYNTHESIS AND CHARACTERIZATIONS OF OXIDIZERS FOR BIOCIDAL NANOENERGETIC APPLICATIONS(2013) FENG, JINGYU; Zachariah, Michael R; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Nanoenergetic materials have been shown to have reactive properties superior to traditional energetic materials since the nanoscale enables more intimate mixing of fuel and oxidizer to reduce the heat and mass transport limitations. The growing threat of biological weapons has prompted research efforts into new energetic materials with biocidal capabilities. Most notably the biocidal nanothermite involves the aluminum fuel with a strong oxidizer, which releases the biocide. In this thesis two kinds of attempted synthesis and characterizations were covered for this biocidal nanoenergetic topic: (1) the highly hygroscopic strong oxidizer I2O5 was successfully passivated into the Fe2O3 shell, which exhibited excellent combustion performance with biocidal capabilities when formulated into aluminum based nanothermite reaction; (2) the copper iodate and iron iodate particles were prepared by co-precipitation and demonstrated to be good candidates for the potential biocidal energetic applications.