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Surface Interactions of DiboraneJones, Nathan B. 22 August 2022 (has links)
Diborane (B2H6) is a hydride gas often employed in high-purity industrial surface processes such as chemical vapor deposition or epitaxial layer growth. The use of diborane at industrial scales is complicated by the formation of higher-order borane contaminants in pure diborane gas via a complex series of gas-phase reactions. An advanced, rationally designed sorbent could stabilize diborane through interfacial interactions, dramatically reducing the decomposition rate without permanently trapping the molecule. However, the design of such a sorbent would require a nuanced understanding of diborane's fundamental surface chemistry, about which little is known. In the work presented in this thesis, a novel ultra-high vacuum (UHV) system was designed and employed to characterize the fundamental interactions of diborane with a variety of surfaces. In situ Fourier-transform infrared (FTIR) spectroscopy and temperature-programmed desorption (TPD) experiments were used in conjunction with density-functional theory (DFT) calculations to elucidate binding geometries and interaction mechanisms. On non-functionalized model surfaces such as CaF2 or amorphous carbon, diborane adsorbed only at cryogenic temperatures. Hydroxylated surfaces such as amorphous silica (SiO2) adsorbed significantly more diborane, which remained at slightly higher temperatures. FTIR spectra indicated the presence of hydrogen bonding between diborane and surface hydroxyl groups. DFT calculations revealed that the interaction takes the form of a novel bifurcated dihydrogen bond. In contrast with previous reports, diborane exhibited only weak interactions with the surface hydroxyl groups of silica. DFT calculations further elucidated that the irreversible reaction of diborane with surface hydroxyls is only possible in the presence of a second nucleophile (such as adventitious water). On the metal-organic framework (MOF) UiO-66 NH2, unique chemistry was observed in which diborane reacted with the –NH2 groups of the MOF linkers, yielding stable surface-bound products. DFT calculations determined the reaction mechanism to be dissociative adsorption of diborane, resulting in two amine-bound –BH3 moieties. Importantly, it was found that these fragments persisted at room temperature and could only leave the surface via the reverse reaction. The discovery that diborane can be stored as separate fragments that re-combine to yield the parent molecule has important implications for the development of new diborane sorbents. We hypothesize that surfaces designed with fixed, precisely spaced nucleophiles could enable the reversible storage of diborane. / Doctor of Philosophy / Diborane (B2H6) is a useful but hazardous gas employed in both academia and industry, often in processes that require ultra-high-purity source gases. However, diborane reacts with itself at room temperature, making the contamination of pure diborane very difficult to avoid. This problem could potentially be solved with a specially designed solid material that would sequester diborane without destroying it, but the design of such a material would require a much better understanding of diborane's chemistry with surfaces than currently exists. In this work, we employed ultra-high vacuum (UHV) methods to study the interactions between diborane and a variety of surfaces, with the ultimate goal of determining guiding principles for the design of diborane-stabilizing sorbents. Among the materials we studied were inorganic carbon, silica (SiO2), and a class of advanced microporous materials known as metal-organic frameworks (MOFs). Inorganic materials were found not to interact meaningfully with diborane. A novel hydrogen bond was discovered between diborane and the surface of silica, but the interaction was found to be too weak to provide significant stabilization. Most MOFs behaved similarly to silica. The MOF UiO-66-NH2, however, was found to react with diborane. Through a combination of computer simulations and UHV experiments, the precise nature of the reaction was determined. On the surface of UiO 66 NH2, diborane splits into two surface-bound BH3 molecules, where it is trapped until the reaction reverses. Importantly, it was found that BH3 can only leave the surface by recombining into diborane—effectively storing diborane on the surface to be released later. We hypothesize that this useful chemistry is due to the fixed distance between chemical groups on the MOF surface. This discovery suggests a promising strategy for the design of advanced diborane sorbents.
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Developing Photo-responsive Metal-Organic Frameworks towards Controlled Drug DeliveryEpley, Charity Cherie 14 July 2017 (has links)
The development of therapeutic drugs or drug systems that enhance a cancer patient's quality of life during treatment is a primary goal for many researchers across a wide range of disciplines. Many investigators turn to nanoparticles (~50-200 nm in size) that tend to accumulate in tumor tissues in order to deliver active drug compounds to specific sites in the body. This targeted delivery approach would reduce the total body effects of current cancer drugs that result in unwanted (sometimes painful and even fatal) side effects. One of the main obstacles however, is ensuring that drugs incorporated into the nanoparticles are anchored such that premature drug release is prohibited. Also, while it is important to ensure strong drug-nanocarrier interactions, the nanocarrier must be able to release the drug when it has reached its biological target. We have developed a nanocarrier that provides a platform for drug systems that could achieve this drug release via the use of a light "trigger".
Metal-Organic Frameworks (MOFs) are a relatively new class of often highly porous materials that act as "sponges" for the absorption of various small molecules. MOFs are so named because they consist of metal clusters that are linked by organic compounds to form networked solids that are easily tuned based on the choice of metal and organic "linker". We have developed a MOF nanocarrier incorporating benign zirconium (IV) metal clusters bridged by an organic component that changes shape when illuminated with a light source. The resulting material is therefore not stable upon irradiation due to the organic linker shape change that disturbs the MOF structure and causes it to degrade. When loaded with drugs, this photo-enhanced degradation results in the release of the cargo thereby, providing a handle on controlling drug release with the use of a light trigger. We have demonstrated that in the presence of the MOF nanocarrier incorporating 5-fluorouracil (a clinically available cancer drug), very low toxicity to human breast cancer cells is observed in the dark, however, cell death occurs in the presence of a light source. These reports offer a model MOF nanocarrier system that could be used to incorporate various drugs and therefore tune the system to an individual patient's needs.
Furthermore, we also developed a material that is capable of providing magnetic resonance imaging (MRI) contrast by changing the metal to manganese (II). MRI contrast agents are compounds that serve to either darken or brighten an MRI image based on the agent used and therefore they aid in clinical diagnosis by making internal abnormalities easier to spot. Currently gadolinium (III) complexes are the most widely used contrast agents; however, the toxicity of gadolinium (III) has been shown to be responsible for the development of nephrogenic systemic fibrosis in some patients. This manganese material has also shown useful for the attachment of fluorescent dyes that can aid in the benchtop optical diagnosis of biopsies. These reports provide a basis for developing ways to offer controlled drug delivery in cancer patients and to aid in cancer diagnosis using MOF materials, in an effort to reach the goals of comfortable cancer treatment. / Ph. D.
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Multifunctional and Moisture Tolerant Zinc-Based Mono- and Bi-metallic Metal-Organic Framework (MOF) thin filmsAgbata, Emmanuel 16 April 2024 (has links) (PDF)
Many applications of metal-organic frameworks (MOFs) are highly dependent on their structures. The type and consistency of structure inform their properties. Zinc-based MOFs are applicable in different fields because of the low toxicity of zinc materials and are therefore also useful for catalysis. While MOF-5, a zinc-based MOF with carboxylate linkers is moisture intolerant, a variant of this is moisture tolerant. The introduction of a nitrogen-based linker in the zinc MOF which renders the structure moisture-tolerant. This material has not been explored as much, despite its multifunctional properties. Furthermore, the growth of Zn-based bimetallics of this MOF has not yet been explored. In this work, I studied the synthesis of this zinc-based moisture-tolerant MOF-5 as a thin film using a simple, fast, and cost-effective layer-by-layer wet synthesis method on different substrate surfaces. I successfully synthesized a series of bimetallics of this MOF as thin films on an untreated silicon wafer substrate. The successful synthesis of these materials was confirmed using X-ray photoelectron spectroscopy, X-ray diffraction, and Raman spectroscopy techniques. Additionally, some software data analysis tools were used for the characterization of the surface of the thin films to quantify the chemical composition. Future applications of these materials will be as sorbent materials for the capture of CO2 and its subsequent conversion to CO which is a synthesis gas for different useful materials like fuel and other chemical materials.
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Synthesis by extrusion: continuous, large-scale preparation of MOFs using little or no solventCrawford, Deborah E., Casaban, J., Haydon, R., Giri, N., McNally, T., James, S.L. 31 January 2020 (has links)
Yes / Grinding solid reagents under solvent-free or low-solvent conditions (mechanochemistry) is emerging as a general synthetic technique which is an alternative to conventional solvent-intensive methods. However, it is essential to find ways to scale-up this type of synthesis if its promise of cleaner manufacturing is to be realised. Here, we demonstrate the use of twin screw and single screw extruders for the continuous synthesis of various metal complexes, including Ni(salen), Ni(NCS)2(PPh3)2 as well as the commercially important metal organic frameworks (MOFs) Cu3(BTC)2 (HKUST-1), Zn(2-methylimidazolate)2 (ZIF-8, MAF-4) and Al(fumarate)(OH). Notably, Al(fumarate)(OH) has not previously been synthesised mechanochemically. Quantitative conversions occur to give products at kg h−1 rates which, after activation, exhibit surface areas and pore volumes equivalent to those of materials produced by conventional solvent-based methods. Some reactions can be performed either under completely solvent-free conditions whereas others require the addition of small amounts of solvent (typically 3–4 mol equivalents). Continuous neat melt phase synthesis is also successfully demonstrated by both twin screw and single screw extrusion for ZIF-8. The latter technique provided ZIF-8 at 4 kg h−1. The space time yields (STYs) for these methods of up to 144 × 103 kg per m3 per day are orders of magnitude greater than STYs for other methods of making MOFs. Extrusion methods clearly enable scaling of mechanochemical and melt phase synthesis under solvent-free or low-solvent conditions, and may also be applied in synthesis more generally. / EPSRC (EP/L019655/1)
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Metal–organic frameworks for organic electrocatalysisTorres Méndez, Carlos Enrique January 2022 (has links)
Metal–organic frameworks (MOFs) represent an important platform to immobilize and stabilize electroactive molecular catalysts due to their porosity, high surface area and well characterized three-dimensional structure. Most efforts in this area have been dedicated to the development of photocatalysts and traditional heterogeneous catalysts based on both precious and abundant transition metals. However, little work has been done to design nickel-based MOF electrocatalysts for organic synthesis. In this work we describe the synthesis of three linkers containing a bipyridine moiety, where two of the linkers are dicarboxylate extended linkers and one is a bispyrazole extended linker. The two dicarboxylate linkers are combined with zirconium clusters to build MOFs of the UiO-n family. The bispyrazole linker was used to synthesize copper-based MOFs. The developed MOFs function as support for the immobilization of nickel (II) species in isolated sites within the frameworks. Following this, the redox properties of these MOFs were studied by the means of electrochemistry. The structure of the organic linkers was confirmed by 1H NMR spectroscopy and mass spectrometry, and two of the linkers are new molecules never synthesized before. The synthesized MOFs were characterized by powder X-ray diffraction, where the MOFs of the UiO-n family showed small crystallite sizes. Similarly, the MOFs based on the bispyrazole linker showed low crystallinity. Metalation of the MOFs with a [Ni(phen)3]Cl2 complex was studied using UV-Vis spectroscopy and scanning electron microscopy, both techniques confirmed the immobilization of the nickel catalyst in the UiO-n MOFs. The electrochemical properties of the MOFs were studied using cyclic voltammetry. Both UiO-n MOFs showed a non-reversible event for the reduction of Ni(II) and the MOFs based on the bispyrazole linker showed a quasi-reversible event for the Cu(II)/Cu(I) couple.
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Multiscale Design of Hybrid Sorbent Materials for Carbon Capture and Enhanced Sorbent Regeneration via Non-Thermal Energy TransferLee, Ga Hyun January 2024 (has links)
This dissertation explores the development and optimization of Metal-Organic Frameworks (MOFs) and Nanoparticle Organic Hybrid Materials (NOHMs) for efficient CO₂ capture and investigates enhanced sorbent regeneration using a non-thermal transfer. Chapter 2 introduces the versatility and challenges of MOFs, including their structural adaptability and issues with hydrostability, highlighting the need for water-resistant modifications or coatings to maintain functionality in humid conditions. Chapter 3 and 4 focus on advancements in MOF design for CO₂ capture and the synthesis of encapsulated MOFs with enhanced durability against moisture, using HKUST-1 integrated with hydrophobic polymer PTMSP as an example to demonstrate its potential despite challenges in optimizing CO₂ sorption efficiency when exposed to water. Chapter 5 explores NOHMs, particularly ionically tethered polyethylenimine (NIPEI), for creating air-filter-like fiber mat systems with significant CO sorption capabilities, even under low CO₂ concentrations and humid conditions, suggesting further material and design optimization for industrial applications.
Chapter 6 presents a modeling study on gas transport behaviors within NOHM-polymer interfaces, utilizing Molecular Dynamics (MD) simulations to enhance our understanding of CO₂ sorption dynamics, pointing towards the importance of ion diffusion rates and the distribution of gas molecules for improved capture efficiency. Chapter 7 delves into CO₂ desorption techniques, comparing microwave radiation to conventional thermal heating, showing the efficiency and energy-saving benefits of microwave regeneration, especially when incorporating Fe₃O₄ magnetite into NOHMs. This chapter also stresses the necessity of innovative reactor designs to ensure uniform heating and address technical challenges like nanoscale temperature measurement and uneven heat distribution.
Chapter 8 extends the discussion to future research directions, emphasizing the potential of NOHMs for CO₂ capture and conversion, the exploration of their electrochemical performance, and the need for understanding CO₂ transport mechanisms for enhanced conversion efficiency. It calls for comprehensive evaluations of sorbents in terms of stability, kinetics, capacity, selectivity, and cost-effectiveness, alongside advancements in microwave regeneration technology to overcome current limitations in sorbent heating efficiency.
Overall, this dissertation underscores the ongoing need for innovative solutions to improve CO₂ capture technologies, highlighting the promise of MOFs and NOHMs in addressing climate change challenges through scalable carbon capture, utilization, and storage (CCUS) applications.
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Syntheses Structural Transformations, Magnetism, Ferroelectricity and Proton Conduction of Metal Organic Frameworks (MOF) CompoundsBhattacharya, Saurav January 2015 (has links) (PDF)
The past few decades have witnessed an almost exponential increase in interest in the field of metal organic frameworks (MOFs), which can be evidenced from the large number of scientific articles being published routinely in this area.
The MOFs are crystalline hybrid materials built via the judicial use of inorganic
metal ions and organic linkers, thereby bridging the gap between purely inorganic
and organic materials. The structural versatility and the potential tunability of the MOFs imparts unique physicochemical and thermomechanical properties, which have
rendered them immensely useful in the branches of chemistry, material science,
physics, biology, nanotechnology, medicine as well as environmental engineering.
The MOFs have been shown to be promising as materials for gas storage and separation, sensors, ferroelectric and non-linear optical materials, magnetism, catalysis, drug delivery etc and researchers have been devising strategies to utilize
the MOFs to tackle a number of global challenges of the twenty-first century.
A survey of the literature reveals that the linear organic linkers, 1,4-
benzenedicarboxylic acid (BDC) and 4,4’-biphenyldicarboxylic acid (BPDC), have been
the organic linkers of choice for the construction of stable, porous and multifunctional MOFs. The aim of this thesis has been to monitor the effect that the presence of a functional group in between the benzene rings of the BPDC would have on the overall structures and the properties of the MOFs. Thus, as part of the investigations, the preparation of the MOF compounds using 4,4’-sulfonyldibenzoic acid (SDBA) and 4,4’-
azodibenzoic acid (ABA) have been accomplished. Along with the conventional
hydrothermal and solvothermal synthetic techniques, the liquid-liquid biphasic
reaction method was also utilized for the synthesis of some of the compounds. The
structures of the compounds were ascertained from single crystal X-ray diffraction
technique. Proton conductivity studies were performed on Mn based porous MOFs
using AC impedance spectroscopy. The ferroelectric behavior in a Co based porous
MOF was established using dielectric and polarization vs electric field measurements.
The labile nature of the lattice solvent molecules was established utilizing single
crystal X-ray diffraction studies and water sorption experiments. In addition, the site
selective substitution in a homometallic MOF and the subsequent conversion to a
mixed-metal spinel oxide upon thermal decomposition, have also been studied.
Chapter 1 of the thesis is a brief overview of the metal organic framework compounds and summarizes the various important structures that have been reported in literature and the interesting properties that they exhibit. In chapter 2, the proton conductivity behavior, solvent mediated single crystal to single crystal (SCSC) and related structural transformations in a family of Mn and Co based porous MOFs with SDBA have been presented. Also presented are the results of the site selective substitution of Mn by Co in a homometallic Mn based MOF and it’s
subsequent decomposition to CoMn2O4 spinel oxide nanoparticles.
In chapter 3, the syntheses, structures and the magnetic properties of the pentanuclear Mn5 based MOF compounds with SDBA have been presented. The role of the time and the temperature in the formation of the compounds has also been presented.
In chapter 4, the dehydration/rehydration mediated switchable room temperature ferroelectric behavior, the single crystal to single crystal solvent exchange studies and selective gas sorption behavior in an anionic Co based MOF with SDBA has been discussed.
In chapter 5, the use of the liquid-liquid biphasic synthetic route in the
formation of Zn and Cd based MOFs with ABA has been discussed. Structural
transformations between the one dimensional Zn based compounds and the heterogeneous catalytic studies using the Cd based compounds have also been presented.
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Development and characterization of a colloidal fluorescent ZIF derivative acting as a bio-label for immunoassaysChapartegui Arias, Ander 19 October 2021 (has links)
In dieser Arbeit ein neues bioanalytisches Konzept untersucht, das nanoskalige Zeolith-Imidazolat-Frameworks (ZIFs) als Marker für antikörperbasierte Analysemethoden einsetzt, einschließlich Enzyme-Linked-Immunosorbent-Assay (ELISA) und Lateral Flow Immunoassay (LFIA). Der Vorteil von ZIFs als Marker gegenüber etablierten Materialien ist ihre vielseitige, einfache und kostengünstige Synthese. Dazu gehört die Möglichkeit, niedermolekulare Substanzen für zusätzliche Sensorzwecke zu verkapseln und für eine hohe Selektivität stabil an Biomakromoleküle zu konjugieren. Als modellhafter Zielanalyt von Relevanz wurden Phthalat-Acylester (PAEs) ausgewählt. Die Relevanz des Nachweises von PAEs ergibt sich aus ihren Eigenschaften als endokrin wirksame Chemikalien (EDCs) und krebserregend. In Kombination mit der Tatsache, dass PAEs aufgrund ihrer Verwendung als Weichmacher in Kindergeschirr, Spielzeug, Trinkflaschen und anderen Produkten auf Polyvinylchlorid-Basis in der Umwelt reichlich vorhanden sind, zeigt, wie wichtig der routinemäßige Nachweis von PAEs in Trinkwasser oder Lebensmitteln ist. / This work explores a new bioanalytical concept that employs nanosized Zeolite Imidazolate Frameworks (ZIFs) particles as labels for antibody-based analytical methods, including enzyme-linked immunosorbent assay (ELISA) and lateral flow immunoassay (LFIA). The advantage of ZIFs as labels over established materials is their versatile, facile, and cheap synthesis. This includes the ability to encapsulate low molecular weight substances for additional sensing purposes and for stable conjugation to biomacromolecules for high selectivity. As a model target analyte of relevance Phthalate acyl esters (PAEs) have been selected. The relevance of the detection of PAEs is due to their properties as endocrine disrupting chemicals (EDCs) and carcinogenic. Combined with PAEs being abundant on the environment because of their use as plasticizers in plastic-made tableware for children, toys, drinking bottles and other polyvinylchloride-based products, shows the importance or their routine detection of drinking water or foods being so critical.
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Mimicking the Outer Coordination Sphere in [FeFe]-Hydrogenase Active Site Models : From Extended Ligand Design to Metal-Organic FrameworksPullen, Sonja January 2017 (has links)
Biomimetic catalysis is an important research field, as a better understanding of nature´s powerful toolbox for the conversion of molecules can lead to technological progress. [FeFe]-hydrogenases are very efficient catalysts for hydrogen production. These enzymes play a crucial role in the metabolism of green algae and certain cyanobacteria. Their active site consists of a diiron complex that is embedded in an interactive protein matrix. In this thesis, two pathways for mimicking the outer coordination sphere effects resulting from the protein matrix are explored. The first is the construction of model complexes containing phosphine ligands that are coordinated to the iron center as well as covalently linked to the bridging ligand of the complex. The effect of such linkers is an increased energy barrier for the rotation of the Fe(CO2)(PL3)-subunit, which potentially could stabilize a terminal hydride that is an important intermediate in the proton reduction cycle. The second pathway follows the incorporation of [FeFe]-hydrogenase active site model complexes into metal-organic frameworks (MOFs). Resulting MOF-catalysts exhibit increased photocatalytic activity compared to homogenous references due to a stabilizing effect on catalytic intermediates by the surrounding framework. Catalyst accessibility within the MOF and the influence of the framework on chemical reactivity are examined in the work presented. Furthermore, an initial step towards application of MOF-catalysts in a device was made by interfacing them with electrodes. The work of this thesis highlights strategies for the improvement of biomimetic model catalysts and the knowledge gained can be transferred to other systems mimicking the function of enzymes.
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Mixed matrix membranes comprising metal organic frameworks and high free volume polymers for gas separationsKhdhayyer, Muhanned January 2017 (has links)
This research aimed to develop new composite membranes using a polymer of intrinsic microporosity (PIM-1) and metal organic frameworks (MOFs) for use in gas separations. PIM-1 was successfully synthesised using the high temperature method (40 min, 160 oC) and the resulting polymer was cast into membranes. PIM-1 membranes were chemically modified by reacting hexamethylenediamine (HMDA) with the nitrile group of PIM-1 to form HMDA-modified PIM-1 membranes. Surfaces of PIM-1 membranes were also modified by basic hydrolysis to form amide-modified PIM-1 membranes. These polymer materials were characterized by different techniques (GPC, NMR, ATR-IR, TGA, Elemental analysis and nitrogen sorption analysis). In addition, eight MOF materials [MIL-101(Cr), ED-g-MIL-101(Cr), TEPA-g-MIL-101(Cr), MIL-101(Cr)-NH2, MIL-101(Al)-NH2, UiO-66(Zr), UiO-66-NH2 and UiO-66(COOH)2] were successfully synthesized. They were chosen due to having high surface areas and large porosity. These MOF compounds were characterized using PXRD, SEM, TGA, and low pressure N2.Successful PIM-1/MOF MMMs were fabricated utilising PIM-1 and the MOFs outlined above with various loadings. The highest MOF loading achieved was 28.6 wt. %, apart from MIL-101(Cr)-NH2, for which it was 23.1 wt. %, and MIL-101(Al)-NH2, for which it was 19.8 wt. %. The morphology of MMMs was characterized by scanning electron microscopy (SEM), proving the dispersion of MOF fillers. Novel PIM-1 supported MOF membranes were successfully prepared by depositing ZIF-8 and HKUST-1 layers on the surfaces of unmodified and modified PIM-1 membranes. These materials were characterized using PXRD, SEM, ATR-IR and SEM-EDX. Gas permeation properties of the MOF/PIM-1 MMMs and PIM-1 supported MOF membranes were determined using a time lag method. Most MMMs tested showed an increase in the permeability and stable selectivity as the MOF amount was increased. However, this was not true for MIL-101(Al)-NH2, where the permeability and selectivity decreased. In contrast, PIM-1 supported ZIF-8 and HKUST-1 membranes caused a sharp decrease in the permeability and increase in the selectivity.
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