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Title: BIO-COMPOSITE NANOMATERIALS; CHARACTERIZATION, MANIPULATION AND APPLICATION
Creator: Kim, Taeyoung
Date: 2013, 2013-05
Description: Biomaterials are any matter or material which interacts with biological system which were present on natural or synthetic nonviable materials....
Show moreBiomaterials are any matter or material which interacts with biological system which were present on natural or synthetic nonviable materials. An ideal biomaterial must physically and chemically compatible for biological applications to avoid toxicity and immune reaction. Collagen is a widely abundant, robust biopolymer that is found in the extracellular matrix (ECM) of many tissues. In terms of its structure and organization, collagen is a bio-nano material. The use of collagen in stem cell differentiation is particularly enticing since it is now evident that the extracellular matrix (ECM) proteins can regulate the cell’s fate and growth by their molecular and physical properties. In this thesis research, we have characterized the physical and structural properties of collagen and its composite materials. We found collagen interacts with NaCl and other nano-materials, such as carbon nanotube (CNT) and TiO2 nanotube, resulting in the modification of collagen structure and increase of its stiffness. In particular, CNT has changed collagen structure at both the molecular level and the higher organizational level. The effects of the matrices on cell growth and development were studied. It was found that collagen/CNT matrix specify and accelerate the stem cell differentiation toward neural cells. Since neurons form the foundation of biological circuit, manipulation of neurons in growth has the potential to form desired biological circuit. We also examined collagen in vaginal wall connective tissues, and found that alteration of collagen properties in clinical tissues is correlated to the onset of pelvic organ prolapse.
PH.D in Chemistry, May 2013
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Title: UNDERSTANDING REACTION MECHANISMS AND CONTROLLING REACTIVE SURFACE SPECIES DURING ATOMIC LAYER DEPOSITION OF METAL CHALCOGENIDES
Creator: Weimer, Matthew S.
Date: 2016, 2016-07
Description: Atomic layer deposition (ALD) is a thin film growth technique that relies on self-limiting reactions between vapor precursors and a surface....
Show moreAtomic layer deposition (ALD) is a thin film growth technique that relies on self-limiting reactions between vapor precursors and a surface. Significant progress has been made in the scope of materials grown by ALD, enabled by precursor development and investigation of surface reaction mechanisms; progress is still necessary. This dissertation has two portions. The first is the development of organometallic compounds to engender new material growth by ALD. Second is the development of X-ray absorption spectroscopy (XAS) tools and techniques for observations of the metal coordination environment during ALD. One material that can be difficult to make is doped materials. Composition of a doped material determines the film properties. One example is vanadium doped indium sulfide. This material was purposed as an intermediate bandgap solar absorbing material which can absorb multiple ranges of light. Two new precursors were developed for the growth of indium sulfide and vanadium sulfide. The indium sulfide material grown has shown superior film photocurrent qualities and doping of vanadium into indium sulfide with fine control over atomic placement was achieved. Films were grown that showed secondary absorptions which aligned with theoretical calculations. The flexibility of the V(III) precursor is shown by a short study on the control of the difficult vanadium-oxygen system in the deposition of stoichiometric oxides. To illustrate how XAS can be used in conjunction with other techniques tin dioxide growth from a stannylene precursor and hydrogen peroxide was studied. From ex situ XAS measurements nucleation, growth and termination reaction mechanism were discovered. Next, a mobile ALD reactor allowed for in situ XAS measurements to be performed on “flat” substrates for the first time. Specifically, the local coordination environment and surface reactions were followed while erbium was doped into alumina and coordination environment of manganese was investigated in the growth of manganese-doped zinc oxide, with the ability to probe in-plane versus out-of-plane bonds. These unique in situ XAS experiments allow for greater understand of metal and non-metal precursors as they interact with surfaces. This enhanced understanding enables new precursor development which leads to better control over surface chemistry and new materials.
Ph.D. in Chemistry, July 2016
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Title: STUDIES ON SYNTHETIC APPLICATIONS OF STEREOSELECTIVE AND REGIOSELECTIVE RING OPENING REACTIONS OF AZIRIDINIUM IONS
Creator: Chen, Yunwei
Date: 2014, 2014-12
Description: Aziridinium ions are valuable reactive intermediates in organic synthesis. Regioselective and stereoselective ring opening reactions of...
Show moreAziridinium ions are valuable reactive intermediates in organic synthesis. Regioselective and stereoselective ring opening reactions of aziridinium ions can provide various useful building blocks including optically active vincinal amines, amino alcohols and amino esters. Aziridinium ions are also involved in the biological process of anti-cancer agents. However, aziridinium ions are under-utilized in organic synthesis. In this thesis, we utilize stereoselective and regioselective ring opening reactions of aziridinium ions for synthesis of enantiomerically enriched compounds. Ring opening reactions of aziridinium ions were utilized in intramolecular Friedel-Crafts (FC) reactions for stereoselective and regioselective synthesis of 4-substituted tetrahydroisoquinoline. A series of β-haloamine were prepared as precuresors of aziridinium ions. The reaction conditions for ring opening of aziridinium ions for the FC reactions including temperature, catalysts, and solvents were optimized. Further, the reaction mechanism was studied to prove that the aziridinium ions were formed as the key intermediates during the intramolecular FC reaction. Intermolecular nucleophilic ring opening reaction of aziridinium ions was studied as a convenient method of carbon-carbon formation. Regioselective and stereoselective nucleophilic substitution reactions of aziridinium ions with indole analogues were carried out for the synthesis of optically active tryptamine analogues. The reactions proceeded smoothly to provide the tryptamine analogues in high yield in the presence of halo-sequestering agents, while the reaction provided the tryptamine products in significantly low yield in the absence of halo-sequestering agents. Ring opening reactions of aziridinium ions with malonic esters and Grignard reagents were carried out for the respective synthesis of optically active tryptamine analogues, γ-aminobuyric acid (GABA), and α-amine derivatives. The regiospecific ring opening reactions of aziridinium ions was directly applied for the synthesis of bifunctional ligands which have a potential use in targeted therapy and imaging of cancers. The novel bifunctional chelates with a shorter alkyl spacer C-NETA and 2E-C-NETA as well as the chelates with a longer alkyl spacer 5p-C-NETA were prepared. 5p-C-NETA was conjugated to a cyclic peptide c(RGDyK) as a targeting moiety for use in targeted radiation therapy. In addition, 2E-C-NETA was conjugated to a fluorescent dye Cy5.5 for theranostic applications. The experimental results indicated that the new bifunctional ligands have promising applications in the biomedical field. In summary, stereoselective and regioselective ring opening reactions of aziridinium ions have been successfully applied for the synthesis of optically active compounds such as 4-substituted tetrahydroisoquinolines, tryptamines, γ-aminobuyric acid, α-amine derivatives and the bifunctional chelators. We demonstrated that ring opening of versatile aziridinium intermediates is a strightforward and convenient method for the synthesis of various optically active compounds.
Ph.D. in Chemistry, December 2014
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Title: NANOPORE STOCHASTIC SENSING OF BIOMARKERS IN HUMAN DISEASE
Creator: Zhou, Shuo
Date: 2016, 2016-07
Description: By measuring the ionic current modulation generated by analytes’ electro-osmotic flow through a nanoscale sized pore, nanopore stochastic...
Show moreBy measuring the ionic current modulation generated by analytes’ electro-osmotic flow through a nanoscale sized pore, nanopore stochastic sensing was invented about 20 years ago. Since then, it has been developed as a powerful and versatile tool for the detection of a wide variety of substances, including metal ions, organic molecules, DNA, RNA, peptides, proteins, etc. Compared with other traditional techniques such as immunochemical detection, colorimetric detection, HPLC, and GC/MS, nanopore detection has many advantages. First and foremost, nanopore stochastic sensing does not need to use sophisticated instruments which are convenient for people who do not have professional training in operating a special device. Furthermore, unlike fluorescent methods which rely on fluorophores labeling, nanopore stochastic sensing is a label-free detection method, which is based on the natural characteristics of analytes of interest. Moreover, nanopore sensing does not need complicated pretreatment of samples and can achieve a very low detection limit rapidly. Most importantly, nanopore detection uses only a small amount of sample with a low assay cost. In this dissertation, I summarize my work on nanopore stochastic sensing of proteases and copper ion, i.e., the detection of the HIV-1 protease (HIV-1 PR), trypsin, and copper ion. It is well-known that the HIV-1 protease is a significant biomarker for AIDS, while trypsin for the pancreatic disease. Considerable effort has been devoted to developing highly sensitive and selective sensors for these two important proteases. By taking advantage of nanopore stochastic sensing, two biosensors are constructed where picomolar concentrations of the HIV-1 protease and trypsin can be detected. On the other hand, copper, an essential trace element, is vital to the health of our human being in many ways. For example, the accumulation of cupric ions in human body may explain the origin of Wilson disease; further, the elevated concentration of copper is also pertinent to some symptoms of Alzheimer disease. Hence, the capability to the sensitive and accurate detection of copper ions is crucial to our health and well-being. For this purpose, a real-time and label-free nanopore biosensor is developed for its detection. The successful research efforts in these projects demonstrate the useful application of nanopore stochastic sensing in medical diagnosis, especially in terms of early disease detection. In addition to the high sensitivity and accuracy as well as low assay cost, other advantages of nanopore sensors include instrumental simplicity, ease of use, and extremely rapid data acquisition rates. Such a field-deployable nanopore sensor is useful as a point-of-care device for early disease detection and diagnosis. Just imagine how convenient your medical diagnosis would become with the pocket size nanopore sensor. We can monitor our own health anytime and anywhere: at home, at workplace, or even outside in remote and isolated places.
Ph.D. in Chemistry, July 2016
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Title: COMPUTATIONAL FLUID DYNAMICS AND POPULATION BALANCE MODEL FOR SIMULATION OF DRY SORBENT BASED CO2 CAPTURE PROCESS
Creator: Abbasi, Emadoddin
Date: 2013, 2013-12
Description: Carbon capture and sequestration (CCS) is one of the key technologies needed to mitigate carbon dioxide emission from industrial sources and...
Show moreCarbon capture and sequestration (CCS) is one of the key technologies needed to mitigate carbon dioxide emission from industrial sources and power plants. Development of CFD-based design tool for prediction of the extent of CO2 capture in a regenerable dry sorbent-based technology, in an efficient power plant design (i.e., modern IGCC power plants) was the driving force behind this project. In this study, we established a systematic methodology, starting from investigating the properties of the sorbent and its reaction mechanism, to developing a model for design and scale-up of the reactors that is needed to deploy this technology at larger scales. This dissertation provides a coupled CFD-PBE model based on the novel FCMOM approach with broad application in reaction engineering and reactor design where the polydisperse nature of the phases has strong effect on the hydrodynamics of the system. Detailed investigations of the MgO-based sorbent and its performance toward capturing CO2 from a coal gas stream were performed that result in development of the two-zone variable diffusivity shrinking core reaction model. Furthermore, a baseline design for a circulating fluidized bed (CFB) reactor, using numerical modeling and threedimensional simulations of a full-loop circulating fluidized bed reactor was provided based on the coupled CFD-PBE, which in combination with the reaction model can perform as a base for parametric studies and optimization of the process.
PH.D in Chemical Engineering, December 2013
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Title: ELECTROSPUN COLLAGEN/SILK TISSUE ENGINEERING SCAFFOLDS: FIBER FABRICATION, POST-TREATMENT OPTIMIZATION, AND APPLICATION IN NEURAL DIFFERENTIATION OF STEM CELLS
Creator: Zhu, Bofan
Date: 2017, 2017-05
Description: Biocompatible scaffolds mimicking the locally aligned fibrous structure of native extracellular matrix (ECM) are in high demand in tissue...
Show moreBiocompatible scaffolds mimicking the locally aligned fibrous structure of native extracellular matrix (ECM) are in high demand in tissue engineering. In this thesis research, unidirectionally aligned fibers were generated via a home-built electrospinning system. Collagen type I, as a major ECM component, was chosen in this study due to its support of cell proliferation and promotion of neuroectodermal commitment in stem cell differentiation. Synthetic dragline silk proteins, as biopolymers with remarkable tensile strength and superior elasticity, were also used as a model material. Good alignment, controllable fiber size and morphology, as well as a desirable deposition density of fibers were achieved via the optimization of solution and electrospinning parameters. The incorporation of silk proteins into collagen was found to significantly enhance mechanical properties and stability of electrospun fibers. Glutaraldehyde (GA) vapor post-treatment was demonstrated as a simple and effective way to tune the properties of collagen/silk fibers without changing their chemical composition. With 6-12 hours GA treatment, electrospun collagen/silk fibers were not only biocompatible, but could also effectively induce the polarization and neural commitment of stem cells, which were optimized on collagen rich fibers due to the unique combination of biochemical and biophysical cues imposed to cells. Taken together, electrospun collagen rich composite fibers are mechanically strong, stable and provide excellent cell adhesion. The unidirectionally aligned fibers can accelerate neural differentiation of stem cells, representing a promising therapy for neural tissue degenerative diseases and nerve injuries.
Ph.D. in Chemistry, May 2017
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Title: ENABLING TOOLS FOR SINGLE CELL ANALYSIS
Creator: Li, Zhaoxia
Date: 2011-07, 2011-07
Description: Cells are basic functional units of life. A cell function is mediated by proteins and genes, whose distribution and expression level depends...
Show moreCells are basic functional units of life. A cell function is mediated by proteins and genes, whose distribution and expression level depends remarkably on the microenvironment. In the native environment, individual cells behave differently but communicate with surrounding cells. It is imperative to investigate proteins and genes at the single cell level in their native environment. The current representative single cell analysis methods, fluorescent techniques, are the most direct tools to study a single cell. The commonly used methods to measure protein and gene expression levels in single cells are on the basis of fluorescence labeling, such as fluorescence-activated cell sorting and live cell microscopy. They become more powerful when combine with the use of microfluidic devices. The disadvantages of these methods are, (1) their limited sensitivity doesn’t allow the detection of low-abundance proteins and genes; (2) they are unable to detect the cell-to-cell difference within a population; (3) the cell-sorting based method is lack of spatial resolution since the isolation of cells from the natural environment is required for analysis. To tackle these challenges, we established atomic force microscopy based approaches for in-situ gene and protein analysis on a target single live cell. The methods provide the spatial and quantitative information of cells in their native culture environment. They are effective and sensitive to detect low-abundant proteins and genes. In this thesis work, we developed a novel immunofluorescence assisted affinity mapping (IF-AM) method, in which immunofluorescence provides the guidance to locate a desired type of cell in a cell community for performing affinity mapping to quantify the local protein density at a high spatial resolution. Due to the ability of directly assessing proteins of individual cells, the IF-AM method is shown to be a sensitive tool for xiii resolving subtle differences in the local expression of membrane proteins even at low abundance. In the following work, we improved the accuracy of protein quantification by adapting the separation work based calculation rather than the previously used maximum adhesion force based calculation, and established a practical model to analyze the data systematically. We applied the methods to investigate the membrane proteins TRA-1-81 and E-cadherin on human embryonic stem cells. The heterogeneous distribution of TRA- 1-81 and the homogeneous distribution of E-cadherin as well as the quantitative measurement of the protein local abundance provided comprehensive information in understanding the strategy of hES cells to maintain the stemness during cell proliferation and to initiate the differentiation. An mRNA retrieval method was also developed to perform the gene expression analysis on a single cell of a desired type in a cell community. This was achieved by using a functionalized AFM tip as a bait to bind and retrieve mRNA from a desired single cell, followed by sensitive Quantitative Polymerase Chain Reaction (Q-PCR) analysis. The extraction of mRNA from live cells was performed with non/negligible damage to the cells. The established method here enabled the gene expression analysis of individual live cells at the original sites without disrupting the cell context. Thus the gene expression of a target cell and its surrounding cells can be analyzed in parallel, deriving concrete data for understanding the behavior of one cell in concert with that of the surrounding cells in the same or different cell population. The method was successfully applied in the study of side population cells in ovarian cancer cells. The methods developed in this thesis are versatile, and can be broadly applied to the study of different membrane proteins and genes of various cell types.
Ph.D. in Chemistry, July 2011
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Title: STUDIES ON RING OPENING REACTIONS AND SYNTHETIC APPLICATIONS OF AZIRIDINIUM IONS
Creator: Sun, Xiang
Date: 2013, 2013-12
Description: Aziridinium ions are valuable and important intermediates to prepare complex nitrogen containing compounds. Various enantiomerically enriched ...
Show moreAziridinium ions are valuable and important intermediates to prepare complex nitrogen containing compounds. Various enantiomerically enriched -haloamines were synthesized as precursors to generate aziridinium ions in situ. Optically active aziridinium perchlorates or triflates were prepared and characterized using 1H and 13C NMR. Regioselective and enantioselective ring opening reactions of aziridinium ions with diverse nucleophilies including cyanide, azide, amines, hydride and water were extensively studied. An efficient one-pot synthetic route to enantiomerically enriched alcohols and amine precursors was developed. Development of the adequate bifunctional chelators is a critical step for radioimmunotherapy (RIT) of cancer. The practical and scalable regiospecific ring opening reactions of aziridinium ions with macrocyclic amines were utilized for synthesis of a series of bifunctional ligands including 3p-C-NETA, C-NE3TA, 3p-C-NE3TA, 3p-C-DECA, 3p-C-DE4TA, an optically active (S)-C-NE3TA, and bifunctional DTPA analogues for RIT using 90Y and 177Lu. Preparation of bifunctional chelators that can rapidly form 64Cu complexes with high stability is an imminent goal for effective PET imaging. A series of NOTA and NE3TA-based chelators were prepared. NE3TA-based bile acid conjugates and NE3TA- based dual receptor-targeted conjugates were synthesized and possess potential for application of targeted PET imaging with 64Cu.
PH.D in Chemistry, December 2013
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Title: DEVELOPMENT OF NANOPARTICLE APPLICATIONS IN CELL IMAGING, BIOASSAY AND REACTIVE OXYGEN SPECIES DETECTION BASED ON SURFACE-ENHANCED RAMAN SPECTROSCOPY
Creator: Yiming, Huang
Date: 2011-08, 2011-07
Description: After mid-1970, the exploration of surface-enhanced Raman scattering (SERS) has been studied by many research groups. Compared to traditional...
Show moreAfter mid-1970, the exploration of surface-enhanced Raman scattering (SERS) has been studied by many research groups. Compared to traditional Raman spectroscopy, enormous cross section of molecules can be obtained in SERS by placing the molecules within the electromagnetic field present in metal surfaces. This enhancement is due to resonance between the optical field and surface plasmon of the metal substrate. Nanoshells which are composed of a silica core and a thin gold shell can greatly enhance Raman scattering without the need to pre-aggregate the particles, due to their tunable optical property. In our study, we synthesized nanoshells as our SERS substrates for Raman tags. The stability of nanoshells coated with three different self-assembled monolayers containing poly(ethylene glycol) (PEG) molecules has been studied. Probes with Raman active PEG molecules have been delivered and imaged in macrophage cells and MCF7 cells, based on SERS technique. The benefits of this imaging technique we developed here are: 1) it is faster; 2) it requires less preparation; 3) it can provide the information of nanoshells in a semi-quantitative way in vitro. We also developed a rapid and easy-to-execute half-sandwich bioassay for the detection of low volumes (< 2 μL) of antigens on nitrocellulose membrane, based on SERS. Multiple antibodies with MW from 18.2 kDa to 170 kDa were bioconjugated to polymers and grafted to nanoshell surface to detect antigens on the membrane. SERS-based biosensors were tagged with Raman active PEGs for recognition and quantification. Here, the bioassay showed great sensitivity to very low concentration x viii of antigens and multiplexed testing have been successfully conducted on different antigens simultaneously. Moreover, SERS-based novel reactive oxygen species (ROS) sensors were designed by establishing mixed-monolayer consisting of poly(ethylene) glycol thiol (PEGSH) and either 4-nitrobenzenethiol (4-NBT) or 4-mercaptophenol (4-MP) on the surface of nanoshells. By analyzing the changes in the molecular Raman spectrum, we were able to track the production of hydroxyl radicals in low concentrations (~ 10 μM). The sensors have been delivered into the cells and did not show significant oxidative stress to the cells. Therefore, these designed sensors are very promising for tracking ROS produced by cells when they are under oxidative stress.
Ph.D. in Chemistry, July 2011
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Title: FROM EXPLORATION TO RATIONAL DESIGN OF SELECTIVE PROPANE DEHYDROGENATION CATALYSTS
Creator: Hu, Bo
Date: 2015, 2015-12
Description: Light olefins, e.g., ethene and propene, are important building blocks of chemical industry for the production of fuels, polymers, lubricants...
Show moreLight olefins, e.g., ethene and propene, are important building blocks of chemical industry for the production of fuels, polymers, lubricants and other fine chemicals. Due to the rapidly increasing production of shale gas, conversion of small alkanes in the shale gas, e.g., ethane and propane, to their corresponding olefins via alkane dehydrogenation could be an important industrial process. This thesis has focused on exploring the novel single site heterogeneous catalysts for selective alkane dehydrogenation and investigating the general principles of rational catalyst design to achieve a better performing (e.g., more active, more stable, highly selective) dehydrogenation catalyst. Based on the observed reactivity of ZnO for olefin hydrogenation and activity of Zn-ZSM-5 catalysts for alkane activation, catalytic properties of isolated Zn2+ were first explored for propane dehydrogenation. The 3-coordinate Zn in single site Zn/SiO2 catalyst was demonstrated to be the catalytically active species that was highly selective for the generation of propene by propane dehydrogenation. DFT calculations revealed that slow β-hydride elimination of alkyl intermediates limited the overall activity of single site Zn/SiO2 catalyst. Thus, single site Co/SiO2 was also prepared in order to take the advantage of fast β-hydride elimination. The higher activity of single site Co/SiO2 emphasized the potential of transition metals for alkane dehydrogenation, and propane dehydrogenation reactivity of transition metals was further explored by investigating single site Fe/SiO2 catalyst. By comparing with metallic Fe nanoparticles and bulk phase Fe oxides catalysts, the 3-coordinate single site Fe2+ was also suggested to be the catalytically active species for selective propane dehydrogenation. However, the catalytic activity of single site Fe/SiO2 catalyst was lower than that of Zn/SiO2. Such result suggested heterolytic cleavage of C-H bonds was slow for transition metals, e.g., Co and Fe, due to their weak Lewis acidity, and it may mitigate the advantages gained in rapid β-hydride elimination. An exploration of ligand effects for improving heterolytic cleavage over single site heterogeneous catalysts was performed. The strength of metal oxygen bond governed by ligand electron donating effects and ligand basicity were found to be the critical chemical descriptors for a facile heterolytic cleavage. Those observed principles of ligand effects would lead to a new strategy of rational catalyst design for a superior dehydrogenation catalyst.
Ph.D. in Chemistry, December 2015
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Title: NEW SOLID AND LIQUID ELECTROLYTES FOR LITHIUM RECHARGEABLE BATTERIES
Creator: Mei, Xinyi
Date: 2016, 2016-12
Description: Currently, rechargeable lithium batteries are widely used in our consumer electronic products, including cell phones, laptop computers, and...
Show moreCurrently, rechargeable lithium batteries are widely used in our consumer electronic products, including cell phones, laptop computers, and cameras and so on. They have extraordinary potential for application in electric and hybrid electric vehicles by their high energy and power density[1]; however, the major challenges include the higher cost, safety issues related to the solvents and conductibility at lower temperatures are still waiting to be fixed. In this Ph.D. thesis, two types of rechargeable lithium batteries: lithium-ion batteries and lithium-sulfur batteries are discussed. Two different approaches are presented, in the direction of achieving an enhanced electrolyte system for rechargeable lithium batteries. One approach is based on the conventional poly (ethylene oxide) (PEO)-based solid polymer electrolyte (SPE) system. The key feature of this approach is the preparation of nanoparticle lithium salts (NPLS) and low lattice energy fluorinated di-lithium salts. The ionic conductivities of these PEO-based SPEs were markedly improved, due to a decrease in the glass transition temperature (Tg) of the polymer. For lithium-sulfur (Li-S) batteries, the polysulfide shuttle (PSS), caused by the dissolution of cathode polysulfide intermediates into the electrolyte, has delivered a mortal blow to nearly every attempt at obtaining a viable Li-S battery. So, another approach involved the strategic design and synthesis of a series of room temperature ionic liquids (RTILs) to prevent PSS: i) Three series of di-cationic ionic liquids (DILs) are synthesis and characterized. DILs-based electrolytes displayed excellent properties, such as non-flammability, high electrochemical stability and thermal stability. ii) Twelve new asymmetric fluorinated RTILs (FRTILs) were also introduced. The FRTILs based electrolytes showed even better properties than DILs-based electrolytes.
Ph.D. in Chemistry, December 2016
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Title: VANADIUM OXIDE BASED MATERIALS AS OXIDATIVE DEHYDROGENATION CATALYST: SYNTHESIS, CHARACTERIZATION AND PROPERTIES
Creator: Aydemir, Kadir
Date: 2013, 2013-12
Description: The project concerns with design, synthesis and characterization of molecular and extended structure materials composed of vanadium oxides and...
Show moreThe project concerns with design, synthesis and characterization of molecular and extended structure materials composed of vanadium oxides and evaluation of their catalytic oxidative dehydrogenation (ODH) properties. A long-term objective is to develop an understanding of the structure-property relationships in ODH catalysts. Chapter 1 provides an overview of the field of metal oxides, polyoxometalates, and catalytic oxidative dehydrogenation of propane. This chapter also defines the research problem concerning this thesis and its fundamental and practical significance. Chapters 2-4 describe the synthesis, characterization and ODH properties of a select number of structurally correlated vanadium oxide based materials. The ODH catalysts studied in this work includes molecular compounds - (NH4)8[VIV 12VV 6O42(SO4)0.85(VO4)0.15]·10H2O (NH4-POV) and NH4V10O28, layered structure materials - MgVV 2VIV 2O10·4H2O (MV4) and V2O5, a chain structure - NH4VO3, and a nanostructured three-dimensional framework material - [Co3V18O42(H2O)12 (XO4)]·24H2O (X = V, S) (Co-POV). Their catalytic activities for ODH of propane to propylene - an important industrial feedstock material, were studies and compared in an attempt to get an insight of the structure-property relationships. Chapter 2 discusses synthesis and characterization of a new mixed-valence vanadate, MgVV 2VIV 2O10·4H2O (MV4), an extended structure solid, synthesized hydrothermally and characterized by single-crystal X-ray diffraction, spectroscopic methods, thermogravimetric analyses and temperature dependent magnetic measurements. MV4 represents the first model compound for the naturally occurring mineral melonovanadite, Ca2VV 4VIV 4O20·10H2O. MV4 is an important material with xv structural and electronic properties that are attractive for making it a potential promising ODH catalyst. The framework structure in MV4 consists of vanadium oxide layers crosslinked by {Mg(H2O)4} groups. The vanadium oxide layers are composed of edge shared {VIVO5} square pyramids, forming {V2O8} dimers, which share corners with {VVO4} tetrahedral units. Chapter 2 also discusses synthesis of a novel mixed-valence molecular polyoxovanadate - (NH4)8[VIV 12VV 6O42(SO4)0.85(VO4)0.15]·10H2O (NH4-POV) and its characterization by single-crystal X-ray diffraction, spectroscopic and thermogravimetric analyses. Structure consists of {V18O42} shell composed of 18 edge sharing {VO5} square pyramids, hosting a tetrahedral species {XO4} (X = S, V). Highly reduced molecular structure of NH4-POV makes it a promising ODH catalyst. Chapter 3 describes the ODH properties of a polyoxovanadate based openframework material - [Co3V18O42(H2O)12 (XO4)]·24H2O (X = V, S) (Co-POV). It is composed of {V18O42(XO4)} (X = S, V) building units, which is the molecular cluster present in NH4-POV, interconnected by {-O-Co-O-} bridging groups. Alternatively, since the building unit clusters {V18O42XO4} can be viewed as derived from sheets of V2O5, the 3-D structure of Co-POV can be viewed as made of V2O5 and CoO units. Therefore the ODH property of Co-POV was compared with the ODH property of the molecular cluster NH4-POV on one hand and with the V2O5 and CoO on the other hand. Co-POV was shown to have superior catalytic performance for ODH of propane as compared with its constituent metal oxides, V2O5, CoO and their mixture. ODH of propane reaction over NH4-POV catalyst has higher propylene selectivity of above 60% at moderate temperatures as compared to 37% selectivity of Co-POV catalyst. Supporting NH4-POV on high surface area γ-alumina was shown to improve propane xvi conversion drastically. In this study, highest propylene yield of 13% was achieved at 550 °C by supported NH4-POV catalyst. On the other hand, MV4 showed catalytic activity at marginally low temperature 200 °C due to propane activation energy (Ea) of 27 kJ/mol, the lowest Ea found in this study. Co-POV was utilized as a model compound to describe the effect of varying doses of γ-ray irradiation on the catalytic ODH properties of polyoxometalates for the first time. γ-ray irradiation enhanced catalysts’ selectivity to propylene during the oxidative dehydrogenation of propane. Chapter 4 describes full characterization of the catalysts studied in this work by powder X-ray diffraction analysis, temperature programmed reduction, X-ray absorption fine structure, BET surface area analysis and scanning electron microscopy. Structural changes of catalysts were investigated by comparing characterization results of asprepared, oxygen pretreated and post-catalysis (spent) catalysts. New vanadium oxide phases formed upon oxygen pretreatment. In general, ODH catalysis did not further alter catalysts’ structures.
PH.D in Chemistry, December 2012
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Title: ANALYSIS OF LOW DIMENSIONAL MAGNETIC SYSTEMS CONTAINING CHROMIUM(III) AND COBALT(II) LIGATED BY THE SQUARATE LIGAND: MAGNETIC CHARACTERIZATION, BIOLOGICAL CHARACTERIZATION, INSTRUMENTAL DEVELOPMENT, AND SOFTWARE DEVELOPMENT
Creator: Mcneely, James Halley
Date: 2013, 2013-07
Description: A large series of Chromium(III) and Cobalt(II) complexes containing the C4O4 (squarate) ligand have been synthesized and characterized...
Show moreA large series of Chromium(III) and Cobalt(II) complexes containing the C4O4 (squarate) ligand have been synthesized and characterized magnetically. These complexes include simple dimeric Cr(III) systems that display a wide range of isotropic exchange couplings. One of these dimers shows interesting biological activity pertaining to the cellular uptake of glucose. This same compound also enhanced proton relaxation in T1 and T2 NMR studies. Computational work done on these dimeric systems showed excellent agreement with experimental results, and was used to confirm the structure of the complexes. The effect of the bridging squarate ligand was also studied computationally. The squarate ligand significantly contributed to the exchange coupling in the dimeric systems, and was shown to behave countercomplementary to the μ-hydroxo bridges. This is the first explicit observation of countercomplementarity in Chromium(III) systems. Co3(OH)2(C4O4) · 3H2O, a cobalt chain structure featuring an interesting low temperature spin-idle phase, was also synthesized. It was found that based on storage conditions, this compound either stays stable after grinding or transforms into the structure Co(C4O4)(H2O)2. In addition, grinding the sample shows an out-of-phase maxima at ≥6 K that has a frequency dependence characteristic of a spin glass. A new software package was also developed to simulate Electron Paramagnetic Resonance (EPR) spectra using full numerical diagonalization of the secular equation. This program was written using Wolfram Mathematica, and holds several advantages over currently available software. These advantages include a graphical user-interface and parallelization capabilities
PH.D in Chemistry, July 2013
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Title: UNIDIRECTIONALLY ALIGNED COLLAGEN / COLLAGEN COMPOSITE FIBRILS AND THEIR MODULATION OF CELL BEHAVIORS
Creator: Li, Wen
Date: 2016, 2016-05
Description: One of the main goals of tissue engineering is to create new functional scaffolds with desired chemical and physical features mimicking the...
Show moreOne of the main goals of tissue engineering is to create new functional scaffolds with desired chemical and physical features mimicking the native micro-environment and modulating cell functions or behaviors. As collagen is abundant in the extracellular matrix (ECM) of native tissues, it is widely used to generate artificial scaffolds in in vitro. In this thesis research, aligned collagen and collagen-composite fibirls (COL-CNT and COLI-COLIII) were achieved via epitaxial growth of collagen on muscovite mica surface. It was found that hdpPSCs interacted with collagen fibrils by deforming the cell shape, harvesting the nearby collagen fibrils, and reorganizing the fibrils around the cell body to transform a 2D matrix to a localized 3D matrix. Such a unique 3D matrix prompted high expression of β-1 integrin around the cell body that mediates and facilitates the stem cell differentiation toward neural cells. By compositing collagen with carbon nanotube (CNT), aligned COL-CNT fibril was obtained with 3 times stiffer than pure collagen fibril and a 2 nm D-period increase. The anisotropic morphology and high stiffness of COL-CNT fibrils greatly facilitated the elongation of SKOV3 cells byregulating the cell-matrix adhesion, cytoskeleton arrangement and cell migration rate, finally promoted the epithelial-mesenchymal transition (EMT) of the SKOV3 cells. Aligned COLI-COLIII hybrid collagen fibrils exhibit higher stiffness than pure COLIII and stronger binding affinity than pure COLI. It is found that with the combined advantages of stiffness and binding affinity, aligned COLI-COLIII fibrils lead to fibroblast cytoskeleton elongation and enhanced cellular elasticity with stronger traction strain sulfured, which improves collagen synthesis ability of fibroblast with a higher collagen I percentage.
Ph.D. in Chemistry, May 2016
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Title: NOVEL ELECTROLYTES FOR LITHIUM-ION BATTERIES
Creator: Ma, Qiang
Date: 2014, 2014-12
Description: With the increasing needs for creating new clean and sustainable energy sources to substitute traditional fossil fuel at present, lithium-ion...
Show moreWith the increasing needs for creating new clean and sustainable energy sources to substitute traditional fossil fuel at present, lithium-ion batteries as one of the most promising energy storage devices have been shown much attention. As a necessary and important component in a battery system, electrolytes need to be expanded according to the cell's requirements for varied applications. Especially nowadays, researches for safe, environmentally friendly and cost effective battery electrolyte systems are very challenging and active all around the world. This dissertation describes three different approaches to achieve an improved electrolyte system for lithium-ion batteries. For solid polymer electrolytes (SPEs), three different plasticizers have been synthesized and incorporated into a conventional poly(ethylene oxide) (PEO)-based SPEs. The room temperature ionic conductivity was significantly improved by decreasing the glass transition temperature of the polymer matrix. One new poly(ethylene glycol)-grafted-polybutadiene was designed and synthesized. Different weight ratios of new co-polymer and PEO mixtures were studied for using as polymer host for SPEs. For liquid electrolytes, two different strategies have been investigated. One is that series of small molecular weight molecular liquids were designed and synthesized to improve the low temperature performance and safety of commonly used organic carbonates systems. Different concentrations of lithium bis-trifluoromethanesulfonimide (LiTFSI) solutions were studied to find the optimized combinations. A series of new zwitterionic liquids (ZILs) were also designed and synthesized as ionic liquid electrolytes. However, this type of electrolytes is too viscous to provide a satisfied ionic conductivity, thus 2-nitropropane as a co-solvent was used here to reduce the viscosity. Last, a series of novel diphosphate-based tetra lithium salts was synthesized and studied. Solartron electrochemical analyzer was used to test ionic conductivity, electrochemical window and lithium cation transference number. The technologies of thermal gravimetric analysis and differential scanning calorimetry were used to study thermal properties of electrolytes. Furthermore, some future plans of studies in lithium-ion battery electrolyte field were also discussed.
Ph.D. in Chemistry, December 2014
Ph.D. in Chemistry, December 2014
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Title: SYNTHESIS AND STRUCTURAL INVESTIGATION OF POLYOXOVANADATE SYSTEMS FOR SEMICONDUCTOR NOx SENSING
Creator: Ravikanth Putrevu, Naga
Date: 2013, 2013-12
Description: Nitrogen oxides (NO and NO2 collectively termed as NOx) are the common air pollutants produced from various indoor and outdoor activities. It...
Show moreNitrogen oxides (NO and NO2 collectively termed as NOx) are the common air pollutants produced from various indoor and outdoor activities. It can cause several environmental problems like ground-level ozone, acid rain, particulate matter, smog formation and health problems like malfunctioning of lungs, damaging air flow passages and creating respiratory problems. To detect these gases, sensors with greater sensitivity, lower recovery time and longer life time are needed. Despite the advantages, of the most widely used NOx sensing materials, semiconducting metal oxides have the limitations like higher operating temperatures and unable to customize the materials with better sensitivity and selectivity. So the current research discusses about a new class of metal oxide systems called polyoxovanadates (POV) and its suitability for the ambient operating conditions. These POVs are basically the vanadium oxide clusters synthesized in top-down and bottom-up synthesis procedures. The main advantages of these systems are possible to synthesize in various sizes, shapes, geometries and dimensions which can help identifying the suitable material for a specific gas. The experimental part discusses about the synthesis, characterization and semiconducting sensing properties of different POV systems using various atomic and molecular spectroscopic techniques. In Chapter 2, a 3-D open framework polyoxovanadate material, [Cd3(H2O)12V16 IVV2 VO36(OH)6(AO4)]·24H2O, (A=V,S) (1), composed of secondary building blocks ({V18O42(AO4)} (A=V,S) clusters) interconnected by {-O-Cd-O-} bridging groups, was chosen for understanding the effect of atmospheric oxygen on 1 electronic properties like band gap and resistance, considering the oxygen as a common xiv interferent in ambient gas sensing. The results explain that 1 interacts with oxygen during the aging process and results changing the vanadium oxidation state from +4 to +5 and expanding the coordination sphere of vanadium from 5 to 6. This expansion can alter the band gap by overlapping the more number of O 2p orbitals with V 3d orbitals and resulting the decrease in resistance. The experiments conducted on molecular {V18O42(AO4)} (A=V,S) cluster, (NH4)8[VIV 12VV 6O42(SO4)]·10H2O, (2a), in Chapter 3, also shown the similar change in band gap and resistance during aging process. Based on the results obtained in Chapter 2 and Chapter 3, a {VO6} containing vanadium oxide cluster, (NH4)2[Ni(H2O)5(NH3)]2[V10O28]·4H2O (4), was synthesized and proved in Chapter 4, that the higher coordination number help lowering the band gap and the resistance without need of aging. In Chapter 5, the NOx sensing properties of 1, 2a, 3 and 4 were studied and compared with well studied NOx sensing material, WO3. Based on the sensing characteristics, 1 shows good sensitivity and response time towards both NO and NO2 under ambient conditions than all the other materials. The FTIR spectroscopy results indicated that the NO2 sensing mechanism occurs via nitrate formation.
PH.D in Chemistry, December 2013
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Title: SYNTHESIS AND POST-SYNTHETIC MODIFICATION OF TETRAZINE-BASED ORGANIC FRAMEWORKS
Creator: Kang, Lili
Date: 2016, 2016-05
Description: Porous organic polymers (POPs) have been studied extensively over the past decade. The intrinsic porosity and tunable chemical structures have...
Show morePorous organic polymers (POPs) have been studied extensively over the past decade. The intrinsic porosity and tunable chemical structures have seen applications in gas storage, separations, and even catalysis. However, a vast majority of the POPs rely on a narrow class of monomeric units and polymerization conditions which limit the diversity of functionality in the polymers, and hence their chemical properties. To get around these issues, a micro- and mesoporous tetrazine-based organic framework with BET surface area of 170 m2/g was synthesized through palladium catalyzed cross-coupling reaction. The structure of the polymer was confirmed by solid-state 13C NMR, ATR-IR, and EDX. The 1,2,4,5-tetrazine units on the struts of the framework were active toward inverse electron-demand Diels-Alder reactions, allowing for a post-synthetic introduction of different functionalities into the tetrazinebased organic frameworks (TzOF). The structures of modified polymers were verifed by solid-state 13C NMR and ATR-IR. To eliminate the use of transition metals during synthesis, a new class of sulfur-containing tetrazine-based organic framework was designed and synthesized by nucleophilic aromatic substitution reactions. The resulting mesoporous polymer framework, with 3,6-dithio-1,2,4,5-tetrazine unit on the struts, showed BET surface are of 38 m2/g. The structure of the framework was confirmed by ATR-IR and EDX. Post-synthetic modifications of the polymer were also achieved by reacting with dienophiles through inverse electron-demand Diels-Alder reactions. The structures of modified polymers were verified by ATR-IR. These two synthetic methods we have developed for tetrazine-based organic frameworks and their ability to introduce functionality post-synthetically brought additional functionalities to the POP family.
Ph.D. in Chemistry, May 2016
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