Browsing by Author "Wong, Michael S"
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Item Adsorptive Removal of Sulfur Containing Compounds from Marine Fuel using Metal Loaded Zeolite Y(2017-04-19) Lobb, Jake Robert; Wong, Michael SThe removal of sulfur containing compounds from liquid fuels is becoming increasingly important. The International Maritime Organization (IMO), the governing body that regulates international maritime trade, has recently passed regulation that significantly decreases the total allowable sulfur content in fuels in order to reduce SOx emissions from merchant vessels. Furthermore, certain applications, such as the operation of fuel cells, require exceptionally low sulfur fuel in order to mitigate catalyst poisoning in the reformer. To this end, the two fuels that were investigated in this work were Intermediate Fuel Oil 380 (IFO380), a common heavy marine fuel, and Jet Propellant 8 (JP – 8), a military logistic fuel desirable for use with fuel cells. The primary desulfurization method used at refineries is hydrodesulfurization (HDS), which is highly effective for sulfur removal of aliphatic sulfur compounds, but remains inefficient at removing refractory sulfur compounds. Therefore, alternative desulfurization methods have been heavily researched which aim to more efficiently remove these compounds after the refining process. In this work, adsorptive removal of sulfur compounds via a batch reactor was chosen for investigation using sodium zeolite Y loaded with copper or nickel (NaY, CuY, and NiY, respectively). It was found that adsorptive desulfurization with metal loaded zeolite Y is capable of removing sulfur compounds from IFO380. The sulfur removal decreased as follows: CuY = NiY > NaY. The sulfur removal, however, was limited as compared to the JP – 8 results. Presumably, the decreased performance was due to the active sites in the zeolite being inaccessible to the large sulfur compounds that likely exist in IFO380, including the significant amount of sulfur contained by the asphalthenes in the fuel. A two-step batch reactor desulfurization technique was used to adsorb sulfur compounds in JP – 8, with the most effective two – step series being CuY – CuY. It was concluded that CuY is the most effective adsorbent for this fuel due to its bonding mechanism allowing it to selectively remove sulfur compounds over competing non-sulfur compounds. Prior to conducting desulfurization experiments, the adsorbents are activated at high temperature under helium gas. During activation, it is well known that the Cu2+ ions within the CuY partially reduce to Cu+. However, there is much disagreement in literature as to the extent of this reduction and which activation conditions contribute. This work investigates the reducibility of copper species within CuY, after various activation conditions under inert gas or reducing agent, using hydrogen – temperature programmed reduction. Through this method, the location of Cu2+ species within the zeolite frame work can be determined, as well as the relative amounts of Cu2+, Cu+, Cu0, and CuO that exist. It was shown that the reducibility of copper species is a strong function of activation temperature and gas and not a function of activation time.Item Advanced Reduction of Nitrogen-Oxyanions Using Precious Metal-Based Model Catalysts(2020-08-14) Guo, Sujin; Wong, Michael SNitrate (NO3−) is a contaminant detected globally in surface water and underground aquifers. Nitrate pollution occurs due to the overuse of nitrogen-rich agriculture fertilizers, wastewater discharge, and contaminant leaching from landfills. This anion, in addition to its partially reduced form, nitrite (NO2−), can cause adverse health effects in humans including methemoglobinemia (blue baby syndrome), and is a suspected carcinogen. Pd-based catalytic reduction of nitrate and nitrite to nontoxic dinitrogen has emerged as an advanced treatment technology for drinking water decontamination. The primary goal of this work is to better understand the catalytic mechanisms of nitrate reduction using structure-controlled model palladium (Pd)-based catalysts to catalytically remove NO3−/NO2− from drinking water. The effects of surface coverages of metal promoter, catalyst support, and other promoting metals were explored. This work provides new insights into the reaction mechanism, and the design of catalysts with enhanced activity and selectivity in addition to deactivation resistance in model drinking water. Bimetallic Pd-based catalysts have been found to be promising for treating NO3−/NO2− contaminated waters. Those containing indium (In) are unusually active, but the mechanistic explanation for catalyst performance remains largely unproven. Different surface coverages of In deposited on Pd nanoparticles (NPs) (“In-on-Pd NPs”) exhibited room-temperature nitrate catalytic reduction activity that varies with a volcano-shape dependence on In surface coverage. The most active catalyst had an In surface coverage of 40%, whereas monometallic Pd NPs and In2O3 have nondetectable activity for nitrate reduction. X-ray absorption spectroscopy (XAS) results indicated that In is oxidized in the as-synthesized catalyst; reduces to zerovalent metal in the presence of H2, and reoxidizes following exposure to NO3−. Density functional theory (DFT) simulations from collaborators suggested that sub-monolayer coverage amounts of metallic In provide strong binding sites for nitrate adsorption and lower the activation barrier for the nitrate-to-nitrite reduction step. This improved understanding of the In active site expands the prospects of improved denitrification using metal-on-metal catalysts. The use of magnetic iron oxide (Fe3O4) support was also used to explore the recyclability and reusability of Pd-In nanoparticles. Magnetic catalysts offer the possibility of rapidly eliminating NO3−, without generating a secondary waste stream, and easily reusing for multiple reactions. In order to evaluate the function of Fe3O4 magnetic core, a four-component catalyst (Pd-In/nFe3O4@SiO2) was synthesized and NO3− reduction reaction was conducted in both clean water and simulated drinking water (SDW). The magnetically recoverable bimetallic Pd-In material exhibits excellent chemical stability, reusability, and high nitrate removal efficiency. The Pd-In/Fe3O4@SiO2 contains nanocrystalline magnetite with a silica shell upon which indium-decorated palladium nanoparticles were attached. The SiO2 shell slowed down iron leaching from Fe3O4 and the bimetallic nano-domains showed nitrate reduction activity in deionized (DI) water without obvious deactivation through multiple recovery and reuse cycles. This magnetically responsive reusable catalyst, which retained activity in simulated drinking water, can serve as a design basis for materials to degrade other oxyanion water contaminants. Lastly, the promotional effect of gold in trimetallic InPdAu was explored for nitrate hydrogenation. A range of mixed alloy PdAu nanoparticles (NPs) were synthesized with varying Pd:Au atomic ratios (90:10 to 10:90), before depositing submonolayer amounts of In metal. The resulting series of In-on-PdAu NPs especially Pd-rich samples had higher activity than In-on-Pd NPs for nitrate hydrogenation, due to optimized electronic and ensemble effects between Pd and Au that resulted in acceleration of the intermediate reduction of the overall hydrogenation reaction. The Au-rich NPs had lower activity, likely due to over-dilution of Pd surface that resulted in unfavorable hydrogen and nitrate/nitrite binding energies. In-on-PdAu generally showed higher N2 selectivity than In-on-Pd, respectively. In-decorated mixed PdAu alloy structure further enhances nitrate reduction performance and expands the prospects of improved denitrification using metal-on-metal catalysts. In summary, Pd-based catalysts can be tailored for enhanced activity, selectivity, longevity and reusability, and catalytic treatment holds the promise for advanced nitrogen-oxyanions treatment.Item All-Conjugated Block Copolymers for Organic Photovoltaics(2015-04-20) Lin, Yen-Hao; Verduzco, Rafael; Wong, Michael S; Barron, Andrew ROrganic photovoltaics (OPVs) are a promising source of alternative energy due to cost effectiveness and process simplicity. However, the performance of OPVs must be improved to produce viable devices. This can be achieved by optimizing the optoelectronic properties of constituent materials, tuning the nanostructures of materials within active layer of OPVs and defining a well-defined interface between electron-donor materials and electron-acceptor materials. The above opportunities can potentially be addressed with using all-conjugated block copolymers in that self-assembly of block copolymers can lead to well-defined nanostructures driven by thermodynamics. The focus of this thesis is on the synthesis and development of all-conjugated block copolymers in which one block is an electron-donor polymer and the other is an electron-acceptor polymer. We focus primarily on poly(3-hexylthiophene) (P3HT)-based block copolymers in which the electron-donor P3HT is made from Grignard metathesis polymerization (GRIM) and the other block is synthesized by Suzuki-Miyaura polycondensation reaction for wide variety of electron-acceptor polymers. Subsequently, the nanostructures of polymers were studied on a model series of all-conjugated block copolymer: poly(3-hexylthiophene)—block—poly[2,7-(9′,9′-dioctyl-fluorene) (P3HT–b–PF) under different processing conditions with using differential scanning calorimetry (DSC) and grazing-incidence X-ray scattering (GIXS). This reveals strong process-structure-property relationships of all-conjugated block copolymers. Furthermore, using our two-step synthetic route, we prepared an all-conjugated block copolymer poly(3-hexylthiophene)—block—poly[2,7-(9′,9′-dioctyl-fluorene)-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′,-benzothiadiazole)] (P3HT–b–PFTBT) that exhibits over 3% PCEs as the active layer in a solution processed OPV due to the formation of lamellae of the block copolymers and preferential π-π stacking direction of the P3HT perpendicular to the substrate. In addition to covalently linked block copolymers, we applied a quadruple hydrogen group, 2-ureido-4[1H]-pyrimidinone (UPy), as polymeric end functionalities to reduce macro-phase separation in polymer blends. In the polymer blends OPVs comprised of P3HT and PFTBT, the UPy hydrogen bonding group reduces macro-phase separation in polymer blends and leads to improved power conversion efficiency of OPVs from 0.43% to 0.77% under 155 oC annealing condition. This thesis demonstrates that both the covalently linked and hydrogen bonding linked all-conjugated block copolymers are potential to enhance performance of OPVs. Furthermore, with the advancement in synthetic techniques and better understandings on structure-processing-property relationships of all-conjugated block copolymers, we are able to apply those into more emerging conjugated polymers and engineer molecules for efficient energy generation in OPVs.Item Complex fluids at interfaces and interfaces of complex fluids(2015-02-02) Nouri Dariani, Mariam; Chapman, Walter G; Wong, Michael S; Yakonson, Boris I; Veatch, Sarah LThe present thesis deals with two independent projects and is consequently divided into two parts. The first part details a computational study of the fluid structure of ring-shaped molecules and their positional and orientational molecular organizations in different degrees of confinement, while the second part concerns an experimental study of phase behavior and interfacial phenomena in confined colloid-polymer systems. In the first part, ring-shaped molecules are studied using Monte Carlo simulation techniques in one, two and three dimensions. The model used to describe ring-shaped molecules is composed of hard-spheres linked together to form planar rigid rings. For rings of various sizes and for a wide range of densities, positional and orientational orderings are reported in forms of pair distribution functions of the ring centers and correlation functions of the ring normal orientations. Special emphasis is given to understand structural formation at interfaces, i.e., the structure and orderings of these molecules when they are confined to two dimensions. In a plane but the rings themselves are free to rotate around all axes, nematic ordering is observed at sufficiently high densities. In the second part, phase equilibria of confined aqueous colloid-polymer systems are studied experimentally using fluorescence microscopy. Aqueous mixtures of fluorescent polystyrene spheres and polyacrylamide are confined between a glass slide and a coverslip. The phase diagram is determined as a function of the colloidal and polymer concentrations. Liquid-liquid phase coexistence between a colloid-rich phase and a polymer-rich phase occurs at intermediate polymer concentrations, while liquid-solid phase coexistence between a polymer-rich liquid and a colloid-rich solid is observed at high polymer concentrations. Interfacial thickness and tension of the interface between these coexisting phases are measured using image analysis techniques. It is also observed that the colloid-rich solid and liquid domains coarsen mainly by Ostwald ripening.Item Embargo The Design of High Performance Integrated Perovskite-based Devices for Solar Fuels(2023-12-12) Fehr, Austin; Mohite, Aditya D; Wong, Michael SThe critical limitations of solar energy, which are temporal and geographic mismatches with consumption as well as utilization for material manufacturing, can be addressed with solar fuels. However, no direct solar-to-chemical conversion processes have reached commercial scale. Direct, efficient, integrated solar-to-chemical energy conversion via photoelectrochemical cells (PECs) is a promising route to low-cost, scaled solar fuel manufacture. Historical limitations in conversion efficiency and material cost have hindered the deployment of PECs. The recent and rapid advances in halide perovskite solar cells, achieving >26% power conversion efficiency with low material costs and facile processing, have opened new avenues for PECs. In the first chapter, we overcome the key hurdle to perovskite-based PECs through the design of a conductive adhesive-barrier which can simultaneously protect the sensitive optoelectronic components without adding series resistance, achieving 13.4% solar to hydrogen (STH) efficiency with single-junction perovskite solar cells and 20.8% STH with silicon-perovskite tandems. In the second thrust, we conduct a robust technoeconomic analysis to identify further hurdles to commercialization and suggest target metrics and figures of merit for future research to achieve commercially competitive green hydrogen at <$2/kg. In the third and final thrust, we demonstrate a design protocol that reduces the key contributor to panel cost, catalyst material price, by an order of magnitude while preserving or increasing STH and lifetime. This constellation of work will be the bedrock for the commercial proofing of PEC water-splitting, and a platform for other reactions.Item Development of Nanocatalytic-Enabled Systems for Treatment of Anthropogenic Water Contaminants(2022-04-21) Rogers, Tanya K; Verduzco, Rafael; Wong, Michael SVersatile and easily implemented methods for water treatment capable of removing and degrading toxic anthropogenic contaminants (e.g., nitrate (NO3-) and perfluoroalkyl substances (PFAS)) are lacking, motivating the need for novel technologies. Nanocatalytic particles offer favorable properties for remediation, including high capacity, excellent kinetics, and selective chemical transformations. However, prior efforts have not effectively implemented these catalysts approaches for continuous water treatment. In this work, we develop novel systems using nanocatalytic materials and new device architectures for water treatment. We developed a new approach termed Catalytic Capacitive Deionization (CCDI) for adsorption and selective reduction of nitrate (NO3-) to innocuous dinitrogen (N2) via indium deposited on palladium (In-on-pd) nanoparticles. We demonstrate that CCDI can convert 91% of aqueous nitrate to N2 with lower electrical energy per order (EEO) compared to alternative treatment methods. We further investigated CCDI for treatment of per- and polyfluoroalkyl (PFAS), enabled by titanium (IV) oxide (TiO2) nanoclusters. Degradation experiments showed successful decomposition of perfluorooctanoic acid (“C8” - PFOA) to shorter-chain products (“C7” – “C3”) under an applied potential energy (Eapp) great than TiO2 band gap energy (Ebg). Density functional theory (DFT) calculations and hydroxyl radical (•OH) indicator experiments provided insight to the critical roles of energy input and reactive oxygen species (ROS). Lastly, we first report the use of covalent organic frameworks (COFS) as nanocatalysts for photodegradation of PFAS. Three conjugated-COF scaffolds were selected based on density functional theory (DFT) calculations of building block monomers HOMO/LUMO levels. Thiophene-linkers exhibited the best degradation performance during photocatalytic experiments, revealing the photo-oxidation catalytic performance of COFs is primarily governed by the oxidizing ability of monomer photo-generated holes (i.e., the HOMO energy level of thiophene monomer (TTDA) was the most positive). This study shows a new application for COF materials and provides important guidelines on designing COFs with optimal photocatalytic performance for per- and polyfluoroalkyl (PFAS) substances. In summary, we developed three new nanocatalytic-enabled water system architectures for treatment of anthropogenic contaminants.Item Gas Chromatography Study of Sulfur Removal from Jet Fuel Using Nanoporous Materials(2019-06-25) Samaniego Andrade, Samantha Kathiuska; Wong, Michael SAdsorptive desulfurization has been studied as a promising process to produce low-sulfur liquid fuels that achieve more stringent regulations. Although the process has proved to be effective to remove sulfur compounds from liquid fuels, a deep understanding of how the desulfurization occurs is still missing. In this work, gas chromatography coupled with Pulsed Flame Photometric Detector, GC-PFPD, is used to analyze the sulfur content of Jet Fuel samples before and after adsorptive desulfurization using nanoporous adsorbents at different temperatures (30℃ - 180℃). The work aims to investigate if the adsorptive removal is selective to a certain fraction of sulfur compounds in the matrix of Jet Fuel. Also, the effect of temperature on the sulfur removal is studied. It was observed that on jet fuel, sulfur removal increases with temperature, reaching the highest sulfur removal at 180℃ when using CuNa-Y zeolite (Dias da Silva, Samaniego Andrade, Zygourakis, & Wong, 2019). Sequential desulfurization experiments were done to see if the adsorbent can remove all sulfur compounds from jet fuel. At first, selectivity for the lighter sulfur compounds was observed, but after 4 desulfurization steps, all sulfur compounds were removed. This showed the adsorbent can remove all types of sulfur compounds in the matrix of jet fuel no matter their size. Additionally, other materials were tested to evaluate their performance at desulfurization of jet fuel. The materials of choice were three metal organic frameworks (MOFs); the first one is UiO-66, and the other two materials were a modified version of UiO-66, named UiO-66-10 and UiO-66-25, which were prepared with a higher content of hydrochloric acid (HCl), 10% and 25% respectively, to create defects in the structure of the pristine UiO-66. UiO-66 was selected for this work because of its high porosity and for having a pore size bigger than that of CuNa-Y zeolite. In the series of UiO-66 materials, UIO-66-10 showed the best sulfur removal which also increased with increasing temperature, reaching its maximum capacity at 180℃. However, CuNa-Y zeolite still achieves a higher sulfur capacity than UIO-66-10. All the treated samples were analyzed through GC-PFPD to check on any change in the sulfur matrix of jet fuel. In the case of UIO-66 materials, selectivity towards lighter sulfur compounds was observed and this increases as the temperature of treatment increases. This behavior was also observed for the samples treated with CuNa-Y zeolite.Item Oxygenation Catalysis to Enable Sustainable Chemical Production and Wastewater Treatment(2023-03-30) Conrad, Chris Leif; Wong, Michael SModern efforts to mitigate CO2 emissions, meet rising energy demands, and source sustainable feedstocks has highlighted the value of (photo)electrochemical ((P)EC) technologies. This vision relies on numerous half-cell reduction reactions such as H2 from H2O, C-feedstocks from CO2, H2O2 from O2, and NH4+ from N2 or NO2-/NO3-. Critically, these reactions all require coupling to the anodic oxygen evolution reaction (OER) to supply protons and balance charge. In addition to enabling sustainable production, anodic oxidation can also provide an efficient means of treating the associated wastewaters (e.g., EC advanced oxidation processes) through the generation of reactive oxygen species and/or other in-situ biocides and oxidative species. This work leverages a materials design approach to engineer solutions within this water-energy nexus. Specifically, we develop synthesis methods amenable to industrial scale-up (i.e., robust, reproducible, rapid) for key catalytic materials: Ir/Ru-based catalysts for acidic OER, and TiO2 electrodes for water treatment applications. Commercially, H2 production via proton exchange membrane (PEM) electrolyzers is positioned to be the cornerstone of our technology transition in the immediate future. However, reliance on expensive and scarce Ir catalysts for the OER presents an immediate bottleneck risk for deployment. Although numerous catalysts report improved activity (i.e., Ir utilization), their complex synthesis routes can be time-consuming, unwieldy, and impractical. Here, we report a one-pot borohydride reduction synthesis to quickly yield >100 mg of aggregated Ir, Ru, and IrRu nanoparticles with outstanding inter-batch consistency. We further demonstrate this method’s versatility by supporting all three particles onto earth-abundant yttrium oxide, resulting in improved precious metal utilization during OER. However, meeting the aggressive (i.e., 2050, 2070) net-zero proposals will require a rapid diversification of sustainable technologies. For H2 generation, integrated PEC and photovoltaic-EC (PV-EC) devices present the most promising avenues towards highly efficient (i.e., >20%) solar-to-hydrogen technologies. We investigated an array of low-Ir catalysts synthesized through the aforementioned method which exhibit an intrinsic activity of >400 A g-1Ir at 1.55 V vs. RHE in acidic conditions. Crucially, a remarkable stability of 10 days of H2 generation in a prototype solar cell architecture is demonstrated for Ir0.5Ru0.5Ox during liquid flow cell electrolysis at a commercially sustainable loading of only 0.1 mgIr cm-2 (0.1 M HClO4, 1.65 VCell). These results represent one of the first demonstrations of PEC-derived H2 at practical loadings. To highlight other opportunities for EC technologies during this energy transition, a case study in the Oil & Gas industry is performed. Hydraulic fracturing (HF) requires >4 million gal. of water be pumped underground per well to stimulate the release of entrapped hydrocarbons. The associated produced water (PW) volumes exceed 150 billion gallons/year and are projected to grow for at least another two decades. Concerns over the potential environmental impact, along with evolving regulatory and economic drivers, has spurred interest in technological innovation. Here, we suggest “fit-for-purpose treatment” to enhance cost-effective regulatory compliance, water recovery/reuse, and resource valorization. We highlight emerging technologies that may enhance cost-effective PW management as HF activities evolve. Based on this analysis, we further sought to improve the synthesis of one of the most promising materials for EC advanced oxidation: TiO2 nanotube arrays (NTAs). Owning to its simplicity, Ti anodization stands as the prevailing NTA synthesis method. However, this approach is marred by sluggish, inconsistent growth rates (ca. 10 nm/min). Here, we determined a broad set of conditions (at 60V) that allow quick NTA fabrication. By modulating conductivity through bulk electrolyte temperature and the addition of several hydroxy acid species, we achieve consistent growth up to 10× faster than traditional methods. We find that regulating the solution conductivity within a desired region (e.g., ~800 – 1000 µS cm-1) enabled the fabrication of double-sided NTA layers of ~10 µm and ~90 µm NTA in 10 and 180 min, respectively.Item Photoresponse of bowtie nanojunctions(2015-07-28) Evans, Kenneth Mellinger; Natelson, Douglas; Nordlander, Peter; Wong, Michael SPlasmon resonant nanostructures provide a platform for controlling light on subwavelength lengthscales. Integrating plasmonic materials into dielectric environments, as well as its compliment – addressing nanoscale photonic elements with plasmon active geometries – is a challenging aspect of current research in wide variety of scientific disciplines including microscopy, photovoltaics, photonics, and catalytic chemistry. This thesis covers two experiments with the goal of electrically and optically addressing nanoscale volumes of semiconducting material using Au nanojunctions with plasmon resonant electrodes. The first measurement aims to use the large field enhancements in bowtie nanojunctions to trap semiconducting nanocrystals from solution. Trapped nanocrystals could then potentially span the gap between the structure's two electrodes to serve as an active optical and electrical region for a number of desirable photoresponsive measurements in single to few nanocrystals systems. We establish a numerical model simulating the force applied on nanocrystals in and around the nanogap as result of the structure's plasmon modes. We also provide experimental data of trapping events in bowtie nanogaps and measurements of the photocurrent generated in the resultant Au-nanocrystal devices. The challenges of this project, mostly related to ligand and surface chemistry, are discussed in detail. In the second experiment, we demonstrate plasmon-enhanced photoconduction in Au bowtie nanojunctions containing nanogaps overlaid with an amorphous Ge film. The role of plasmons in the production of nanogap photocurrent is verified by studying the unusual polarization dependence of the photoresponse. With increasing Ge thickness, the nanogap polarization of the photoresponse rotates 90 degrees, indicating a change in the dominant relevant plasmon mode, from the resonant transverse plasmon at low thicknesses to the nonresonant “lightning rod” mode at higher thicknesses. To understand the plasmon response in the presence of the Ge overlayer and whether the Ge degrades the Au plasmonic properties, we investigate the photothermal response (from the temperature-dependent Au resistivity) in no-gap nanowire structures, as a function of Ge film thickness and nanowire geometry. The film thickness and geometry dependence are modeled using a cross-sectional, finite element simulation. The no-gap structures and the modeling confirm that the striking change in nanogap polarization response results from redshifting of the resonant transverse mode, rather than degradation in the Au/Ge properties. We note remaining challenges in determining the precise mechanism of photocurrent production in the nanogap structures.Item Rh-Based Catalysis Chemistry of Aqueous-Phase Nitrogen Treatment Reactions(2020-12-01) Clark, Chelsea A; Wong, Michael SOver the past century, the increase in human population has driven a need for the increased fixation of atmospheric nitrogen to produce nitrogen-based fertilizers and munitions. These anthropogenic processes have led to significant pollution of freshwater by inorganic nitrogen species (e.g. NO3-, NO2-, NH4+). Nitrate (NO3-) and nitrite (NO2-) consumption is toxic to humans, and ammonia/ammonium (NH3/NH4+) is toxic to aquatic life. Both the oxidized and reduced species contribute towards eutrophication and soil acidification. Catalytic denitrification has emerged as a promising technology for the remediation of nitrogen-contaminated waters. The primary goal of this work is to investigate rhodium (Rh)-based catalysts for the remediation of inorganic nitrogen contaminants in water. This study addresses the effects of pH and salinity on the catalytic mechanism of nitrate/nitrite hydrogenation. A new support material for Rh was developed and a bifunctional reaction mechanism was found for ammonia oxidation. This work provides new insights into nitrogen conversion mechanisms in water over Rh, and insights into the design of active and selective catalysts for a desired treatment application. The NO2- reduction properties of alumina-supported Rh were investigated using Pd as a benchmark, where the bulk solution pH was varied to probe the effect of reaction conditions on the catalytic chemistry. Pd expectedly showed high reduction activity and high N2 selectivity at low pH, and near inactivity at high pH. Rh, while inactive at low pH, showed moderate activity and high NH4+ selectivity at high pH. Hydrazine (N2H4) was also detected as a reaction intermediate when NH4+ was formed. Density functional theory (DFT) simulations of the reactions performed by collaborators revealed new insights into the reaction mechanism at different pH, which were corroborated by in aqua surface-enhanced Raman spectroscopy (SERS). These results update the common view that only Pd-based catalysts are effective for NO2- reduction and suggest unexplored avenues for nitrogen chemistry. The effect of chloride on the NO3- hydrogenation activity and selectivity was evaluated for carbon-supported rhodium and palladium catalysts. In the absence of buffer, chloride monotonically increases the overall catalytic activity of In-Rh/C. In-Pd/C showed a volcano-shaped dependence on the nitrate reduction rate showing lower activity in 2M NaCl than DI water. CO-SERS analysis of chemisorption on model substrates suggested that suggests that NaCl has an electronic effect on both metals which decreases the N-O bond strength of the crucial NO* surface intermediate. The In-Rh/C catalyst also demonstrated high activity for nitrate reduction towards ammonia in simulated ion-exchange brines implying it may be an option for nutrient recovery from these streams. A new Rh supported on a semi-crystalline niobium oxide support was developed to activate aqueous ammonium at room temperature and atmospheric pressure, converting into gas-phase nitrogen species (N2, NO, N2O) and trace amounts of NO3- using only O2. Raman spectroscopy correlated the chemical treatment of the support prior to metal addition to the generation of terminal Nb=O species, which are crucial for catalytic activity. Isotopic experiments reveal a bifunctional mechanism, where Nb binds and converts ammonium to ammonia, which decomposes on Rh. While further optimization is needed to drive selectivity towards N2, Rh supported on modified niobium may be the basis of a new generation of catalysts that can oxidize NH4+ under mild conditions. In addition to nitrogen contaminant degradation for clean water applications, I also investigated Zr-based metal-organic framework (MOF) materials for the adsorptive treatment of perfluorooctane sulfonate (PFOS) contaminated water. In this work, the sorption properties of UiO-66 metal-organic frameworks (MOFs) with varying defect were studied for the removal of PFOS. Large pore defects (~16 and ~20 Å) within the framework were critical to increasing the capacity due to higher internal surface area and an increased number of coordinatively unsaturated Zr sites to bind PFOS head groups. The enhanced PFOS adsorptive properties of UiO-66 highlight the advantage of structurally defective MOFs as a water treatment approach towards environmental sustainability.Item The characterization and visualization of multi-phase systems using microfluidic devices(2015-03-10) Conn, Charles Andrew; Biswal, Sibani L; Hirasaki, George J; Wong, Michael S; Riviere, Beatrice MThe stability and dynamics of multi-phase systems are still not fully understood, especially in systems of confinement such as microchannel networks and porous media. In particular, systems of liquids and gases that form foam are important in a number of applications including enhanced oil recovery (EOR). This research seeks to better understand the mechanisms of multi-phase fluid interaction responsible for the displacement of oil. The answers to these questions give insight into the design of efficient EOR recovery strategies, and provides a platform on which researchers can perform studies on pore-level phenomena. Our experiments use poly(dimethylsiloxane) (PDMS) devices which can be made using inexpensive materials without hazardous chemicals and can be designed and fabricated in just a few hours to save time, money, and effort. The unique contribution of this thesis is the development of a general “reservoir-on-a-chip” research platform that facilitates study of multi-phase systems relevant to energy-industry applications. Experiments with a fractured porous media micromodel quantified pressure drop and remaining oil saturation for different recovery strategies. It demonstrated foam flooding’s superior performance compared to waterflooding, gas flooding, and water-alternating-gas flooding by increasing flow resistance in the fracture and high-permeability zones and directing fluids into the low-permeability zone. Mechanisms of phase-separation were observed which suggest it is inappropriate to treat foam as a homogeneous phase. Experiments with foam in a 2-D porous matrix investigated mechanisms of foam generation, destruction, and transport and related foam texture (bubble size) to pressure drop and apparent viscosity. MATLAB code written for this thesis automated quantification of over 120,000 bubbles to generate plots of bubble size distributions for alpha olefin sulfonate (AOS 14-16) at different foam quality (gas fraction) conditions. The experimental devices and analytical software tools developed in this work open the door for future experiments to screen and compare surfactant formulations. One may readily envision developing libraries of surfactant data from micromodel experiments which can then be data-mined to discover relationships between surfactant structure, performance, and environmental conditions.Item Ultrashort Single-walled Carbon Nanotubes: A Platform for Medical Imaging and Therapy(2015-04-21) Law, Justin Jonathan; Wilson, Lon J.; Tour, James M; Wong, Michael S; Curley, Steven AUltra-short single-walled carbon nanotubes (US-tubes) have been used to encapsulate various metal ions and small molecules for both diagnostic and therapeutic applications. Of the US-tube derivatives, one of the best characterized is the gadonanotube (GNT). GNTs are remarkable due to their greatly enhanced relaxivity, which is up to 40 times larger than current clinically available gadolinium based contrast. The work in this thesis explores the mechanisms contributing to this phenomenon. This is accomplished by using a series of closely related chelating ligands to explore the role of the coordination environment on the loading, retention, and relaxivity of gadolinium ions within the US-tubes. Further, the chelation system is applied to the positron emitting radioisotope 64Cu and concurrent loading with gadolinium ions to produce bimodal imaging agents is discussed. In order to assess the viability of US-tubes as a platform for delivering medically relevant molecules, the biocompatibility of the US-tubes is explored. The cellular uptake and subcellular localization of the US-tubes is determined by Raman mapping and differences in US-tube aggregation and cellular response are analyzed. A strategy for enhancing water solubility of US-tube derivatives while retaining encapsulated ions is discussed. Finally, the heating properties of US-tubes in an external radiofrequency field are assessed to determine potential therapeutic applications.