Browsing by Author "Martí, Angel A"

Now showing 1 - 5 of 5
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    Alkylation of Boron Nitride Nanomaterials using Reductive Conditions
    (2019-04-17) de los Reyes Berrones, Carlos Alberto; Martí, Angel A
    Boron nitride nanomaterials possess an unparalleled combination of properties: their mechanic properties are superior to that of steel, their thermal conductivity is comparable to that of copper, their band gap is that of an insulating material, and their chemical and thermal stability is remarkable. Researchers anticipate that this unique set of properties will have applications in a wide array of fields. However, boron nitride nanomaterials are not perfect. It is their poor dispersibility in solvents and their chemical inertness that have frustrated their comprehensive utilization. The ability to chemically modify these nanostructures could open the door to tune their properties and expand their compatibility with solvents. Therefore, this thesis investigates an unexplored chemical tool for boron nitride nanomaterials: the Billups-Birch reduction.
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    Investigating the Behavior of Boron Nitride Nanomaterials in Aqueous Surfactant Solutions
    (2020-08-10) Smith McWilliams, Ashleigh Dawn; Martí, Angel A
    Boron nitride nanomaterials are an exciting and understudied class of materials with enticing properties for a wide range of applications. They’re extremely lightweight and strong, with high thermal and chemical stability, and a wide bandgap that makes them electrically insulating and transparent to visible light. This unique set of properties makes them exceptional candidates for application in fields ranging from space exploration to drug delivery; however, obtainment of these advanced applications still requires researchers to overcome some large obstacles. Chief among them is the amphiphobic nature of the materials, which makes them difficult to work with in liquid-phase processes that are key to material processing and biomedical applications alike. This thesis investigates how to produce uniform dispersions of boron nitride nanomaterials in aqueous solution, and then, probes how the materials behave within these dispersions using single molecule diffusion studies.
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    Magnetic nanomaterials for applications in magnetic resonance imaging and cancer stem cell biology
    (2014-11-04) Jebb, Meghan Helen; Wilson, Lon J.; Lewis, Michael T; Martí, Angel A; Wagner, Daniel S
    Magnetic nanomaterials are uniquely suited for applications in biology and medicine. With size compatibility, tunable physical properties, and the capacity for external magnetic control, nanoscale magnetic particles have been exploited for drug delivery, hyperthermia-mediated cancer therapy, cell separation and isolation, and magnetic resonance imaging (MRI). This work explores several different nano-based materials for MRI and cancer cell isolation applications. First, Gd3+-loaded carbon nanotube capsules, or gadonanotubes (GNTs), have been analyzed by X-ray absorption spectroscopy to account for the structural contributions to their high MRI contrast enhancement properties. This work revealed the existence of small [Gd-O9] sites in the GNTs with short Gd-O (and thus Gd-H) bond lengths, which contribute to their high performance. Secondly, two new nanomaterials were developed, by loading paramagnetic Mn2+ ions into or onto ultra-short single-walled carbon nanotubes (US-tubes) or GNTs (manganonanotubes and manganogadonanotubes, MNTs and MGTs, respectively). With relaxivity (r1) values of 65 (MNT), 74 (MGT), and 110 (GNT) mM-1s-1 per ion and approximately 13-fold contrast enhancements in all cases over the free ions, US-tubes have been further confirmed as a universal platform for the enhancement of MRI contrast agent properties with the GNTs being the best r1 agents developed to date. Finally, a method for the isolation of quiescent breast cancer cells has been developed, using iron oxide nanoparticles (IONs) as intracellular labels. Once isolated, functional assays were employed to characterize the drug resistance and stem-like nature of the quiescent subpopulation. The project has thus demonstrated how a magnetic nanomaterial-facilitated procedure can be exploited to probe fundamental questions in cancer stem cell biology.
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    Synthesis and design of nanostructured materials for electrochemical energy storage and conversion
    (2015-09-18) Fei, Huilong; Tour, James M.; Ajayan, Pulickel M; Martí, Angel A
    The finite nature of fossil fuels and environmental problems caused by traditional energy sources call for renewable and sustainable energy strategies, including energy storage and conversion. The synthesis and design of nanostructured materials play an important role in the advances of alternative energy systems and devices. Lithium-ion batteries (LIBs) are one of the most important energy storage devices that have been commercially used in daily life. LIBs consist of one positive electrode and one negative electrode, which are separated by a lithium-ion conducting electrolyte. The development of LIBs with high energy density and power density mainly relies on the use of advanced nanomaterials in the two electrodes. For energy conversion, water splitting and the fuel cell are two important clean and renewable techniques to interconvert electrical energy and chemical energy. Water splitting, by applying external electrical energy, generates hydrogen gas on one electrode (hydrogen evolution reaction, HER) and oxygen gas on the other electrode (oxygen evolution reaction, OER). By this process, electrical energy is converted to chemical energy stored in hydrogen fuels. Fuel cells, on the other hand, convert chemical energy into electrical energy by combining hydrogen and oxygen gas into water. The two half-reactions involved are the oxygen reduction reaction (ORR) and hydrogen oxidation reaction (HOR). Due to the presence of kinetic barriers, all of the above four reactions need electrocatalysts to improve their efficiency. This thesis begins with an introduction of energy storage system of LIBs and energy conversion systems of fuel cells and water splitting in Chapter 1. Chapter 2 discusses three different nanomateirals with core-shelled structures and their applications in LIBs and HER. The graphitic carbon shell is demonstrated to improve the cycling stability and rate capability of Fe2O3 as an anode and LiFePO4 as a cathode. In addition, the graphitic carbon shell with a nitrogen dopant can interact with cobalt nanoparticles at the core to give high HER catalytic activity. Chapter 3 describes two different heteroatom-doped nanocarbons for ORR application. One is B, N-doped graphene nanoribbon and the other is B, N-doped graphene quantum dots/graphene hybrid. The edge abundance in the nanoribbon and quantum dots is demonstrated to have a critical role in enhancing the catalytic activity. In Chapter 4, various porous films, including MoS2, WS2, WC, NiCoOx and CoP/CoPO4, are used as binder-free electrodes for water splitting applications. The porous structure is created by the use of anodization technique. Benefited from the high porosity and high surface area, these films show excellent catalytic activity for HER and/or OER. Chapter 5 describes a new type of electrocatalyst for hydrogen generation based on very small amounts of cobalt dispersed as individual atoms on nitrogen-doped graphene. This catalyst is robust and exceptionally active in aqueous media. A variety of analytical techniques and electrochemical measurements suggest that the catalytically active sites are associated with the metal centers coordinated to nitrogen.
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    Synthesis, Modifications, and Applications of Porous Nanostructures
    (2022-11-22) Ling, Kexin; Martí, Angel A
    Porous materials, with their high surface areas, controllable structures, and tunable pore sizes, comprise an interdisciplinary research field in focus today, and one that is developing rapidly. Various porous materials have been adopted for different applications, including adsorption, separation, catalysis, energy conservation, sensing, and drug delivery. Thus, there is an ever-increasing demand for synthesizing porous materials with desired structures and compositions to meet specific requirements. In this thesis, three distinct porous materials will be covered: iron oxide/carbon composite, rhenium carbonyl complex incorporated UiO-67 MOFs, and fluorinated boron nitride nanotubes. Chapter 1 generally summarized the fundamentals about synthetic methods and structural properties of porous materials. The development of the three materials covered in this thesis will also be introduced in detail. Activated carbon is one of the most ever studied porous materials. Its composites with metal oxides show potential for desulfurization. In Chapter 2, we explored the synergic effects in composites of iron oxide (Fe2O3) and oxygenated porous carbon (OPC) for the removal of H2S at room temperature. Two types of Fe2O3-OPC composite samples were prepared: physically mixed (PM) and chemically mixed (CM). The two types of composites were tested for H2S uptake performance at ambient conditions, and a systematic study of the synergic effects of Fe2O3 and OPC was performed. Thorough characterization and analysis were used to reveal detailed structural and compositional properties of these samples. The CM sample with the best uptake capacity was also tested further for the desulfurization rate and the mechanism of action. The PM samples showed a lower H2S uptake capacity within 24 h compared to the theoretical value for the Fe2O3 and OPC working independently, indicating a negative synergic effect. The CM samples reached a maximum uptake capacity higher than the components working independently and importantly an increased rate of H2S uptake, which indicates positive synergy, showing potential in applications where rapid adsorption is required. Directly coordinating transition metal catalysts to the linkers of stable metal organic frameworks (MOFs) is a sleek solution to increasing the longevity of the catalyst. In Chapter 3, Re(bpydc)(CO)3Cl (bpydc = 2,2’-bipyridine-5,5’-dicarboxylic acid) doped zirconium-based MOFs (Re-UiO-67) were synthesized. The photophysical characteristics of Re-UiO-67 as a function of loading were explored. We analyzed the structural and compositional properties of Re-UiO67 and showed that the photoluminescence properties of rhenium doped MOFs, including emission intensity, maximum, and lifetime, can be tuned by changing the rhenium loading. The photoluminescence of the film made of Re-UiO-67 exposed to different vapors also exhibited vapoluminescence, luminescence vapochromism, and vapotemporism. Understanding of photophysical properties of the Re-doped MOFs material could provide guidance for further photocatalytic, solar energy conversion and sensing applications. In Chapter 4, we developed a covalent fluorine functionalization protocol using hydrofluoric acid at room temperature and reached up to 3.7 wt% of fluorine content on the BNNTs. Using spectroscopic methods and thermal analysis, we verified that fluorine was chemically bonded to boron site. Further nucleophilic BNNTs substitution reactions were performed using alkyl alcohol, providing insights into subsequently tuning surface properties of BNNTs from the fluorinated precursor. In addition, we showed that tuning the hydrophobicity of the surface functional groups leads to dispersibility differentiation in different solvents. This sequential chemical functionalization protocol brings a chance to improve the compatibility of BNNTs towards developing composite materials.