Thesis--Wisconsin. / Vita. Includes bibliographical references (leaves 394-420).

Recent technological advances such as the transition from non-renewable to renewable energy have been intimately related to the development of new nanostructured materials. A rational thinking is required for the development of nanomaterials with functional properties by targeting the combination of two or more nanocomponents with different properties, and preparation methodologies ensuring the utilisation of cheaper and abundant materials such as non-precious metals. Therefore, the main motivation of this work is to expand the frontiers of knowledge for the preparation of functional nanomaterials by designing hybrid carbon nanostructures suitable for energy storage applications containing a range of electrochemically active nanocomponents including molecules, nanoparticles and metal coordination polymers. The first chapter describes a general overview of the current approaches within the energy area to prepare uncoupled carbon nanostructures as well as the strategies to combine them with several active components (i.e. molecular metal clusters, nanoparticles and metal coordination polymers). Relevant concepts for this thesis such as electrochemical storage mechanisms, differences between hybrid and composite nanomaterials, synergetic effects and the distinction between ex situ and in situ synthetic approaches are discussed in the introductory chapter. For the sake of clarity, only the most relevant examples of hybrid carbon nanostructures from the literature will be highlighted and discussed. Before describing the hybridisation of carbon with molecules, nanoparticles and metal-coordination polymers, different carbon nanostructures will be analysed on their own due to their outstanding electrochemical properties. After the introductory chapter (Chapter 1), the thesis is followed by two parts: Part A and B. Part A, which is divided in two chapters (Chapter 2 and 3), gathers only carbon nanostructure investigations. In Chapter 2, a facile and solvent-free method is proposed for the development of few-layer graphene nanostructure from carbon tubular nanofibers. In Chapter 3, the synthesis of hollow carbon cages on the surface of carbon nanostructures is thoroughly investigated to elucidate their novel mechanism of formation. The preparation and electrochemical characterization of metal-carbon nanostructures by combining carbon nanostructure with a molecular metal cluster, metal oxide nanoparticles and metal coordination polymers are discussed in Part B. In Chapter 4 the extreme confinement inside hollow tubular carbon nanotubes is investigated to overcome the intrinsic low stability of molecular Mn12 cluster during the electrochemical process. In Chapter 5, the synthesis of metal oxide nanoparticles is carried out in the presence of hollow tubular carbon nanofibers (what we called “in situ synthesis”) where special attention is paid to the carbon surface functionalization. Only the metal oxide-carbon hybrids of interest produced in previous chapter are extensively characterized by electrochemical means to elucidate the effect of confinement with respect to their electrochemical stability. In Chapter 6, a correlation between the structure and chemical composition of a coordinated metal polymer and its electrochemical performance is established in order to gain a better understanding of the alkali intercalation/deintercalation process. One of the key findings in this thesis has been the encapsulation of electrochemically active species, shows promising results not only due to the electron transfer between the guest specie and the host carbon nanostructure, but also to the improvement in the stability during electrochemical cycling. In addition, it has been observed that the electrochemical performance of metal-carbon nanohybrids depends dramatically on the synthetic process that determines the interaction between the nanocomponents and, therefore, the synergetic effect. To sum up, the work developed in this thesis contributes to the area of hybrid metal-carbon nanostructures for energy-storage applications, including new synthetic protocols and strategies, novel hybrid materials with confined electrochemical components, advanced understanding on the electrochemical-structure relationships and important concepts related to durability/recyclability.

Ionic Liquids (ILs) have drawn a great deal of attention as carbon capture agents, and in order to understand them studies must be performed probing the CO2–IL interaction. Many studies have focused upon measuring the solubility of CO2 within ILs, with fewer studies directly probing the CO2 adsorption environments within the IL. Understanding of the adsorption environments is of fundamental for the use of ILs industrially, if they are to be successfully applied within carbon capture and storage devices. Temperature programmed desorption (TPD) has been used to study the CO2–IL interaction within two ionic liquids; 1-octyl-3-methylimidazolium tetrafluoroborate ([C8C1Im][BF4]) and 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C8C1Im][Tf2N]). Experiments were performed utilising low temperature line of sight mass spectrometry (LTLOS MS), ensuring that only species desorbing from the surface are observed. Surfaces were formed through a coadsorption method, where IL was deposited by chemical vapour deposition at a rate of ≈ 1 layer per minute while CO2 was simultaneously leaked into the chamber at pressures between 2×10−8 and 2×10−6 mbar. This study finds that CO2 does not form a monolayer on a gold surface at ≈ 90 K, with no CO2 TPD peak seen for those experiments, showing Edes,CO2 (the activation energy of desorption of CO2) < 24.5 kJ mol−1. When IL and CO2 are coadsorbed the IL is seen to stabilise the CO2, such that a TPD peak for CO2 is seen, with the amount of stabilisation depending upon the IL used. Comparison of experimental TPD curves with calculated TPD profiles, using CO2 states with a range of binding energies, shows that there are multiple CO2 environments within the ILs. The use of TPD allowed the relative populations of these CO2 adsorption environments to be measured, which is not possible using solubility measurements and Henry’s constants, providing insights into the IL–CO2 interaction. CO2 was observed to desorb from sites within the bulk IL, which have activation energies of desorption in the range 24.5 to 43 kJ mol−1. The CO2 was seen to be stabilised most within the [C8C1Im][BF4], giving a stabilisation in Edes of up to 18.5 kJ mol−1. The [C8C1Im][Tf2N] was typically seen to stabilise twice as much CO2 as [C8C1Im][BF4], which is consistent with the experimental Henry’s constants. Further to this a new experimental technique for determining surface structure, utilising high energy X-rays in the total reflection regime, to generate an X-ray standing wave (XSW) and detect the resulting photoelectrons from layered surfaces has been demonstrated. The variable period X-ray standing wave (VPXSW) technique relies on the fact that at low incident angles (typically < 2°) total external reflection of X-rays is observed. The incident and reflected X-rays interact to generate an XSW along the surface normal, with nodes and antinodes at different heights, z, above a reflector for different angles of incidence. By scanning the incident angle of the X-ray from 0° upwards the periodicity of the XSW decreases, resulting in the nodes and antinodes sweeping towards the surface. As this sweeping occurs the nodes and antinodes pass through material adsorbed on the surface of the reflector, and the photoelectron signal fluctuates. Comparing the fluctuations in the measured photoelectron signal to a theoretical model allows surface layering to be detected at larger depths and with a higher information content than with other surface science techniques. This allows distance information, relative to the interfaces between different materials, to be obtained for different chemical species. Data is presented from a surface consisting of the ionic liquid [C8C1Im][BF4] on a Si(001) reflector, held at ≈ 90 K, with a thick IL layer adsorbed on the reflector and a CHCl3 marker layer on top of the IL. Results from the frozen surface indicate a 12 Å layer of CHCl3 and background water had been dosed on top of a 211 Å IL layer. These values agree well with what was expected for this model IL system with a thin marker layer, designed to test the technique. It is therefore shown that VPXSW with photoelectron emission can be used to successfully characterise thin films with thicknesses between 15 Å and ≈ 300 Å with chemical shift specificity, something not possible with current experimental techniques.

No description available.

The present thesis is concerned with the theoretical studies on artificial water splitting process. As the quick development of research on utilizing of solar energy, which is a green, clean, and renewable energy source, many research groups focus their attention on artificial photo-synthesis systems inspired by the photosystem I and II. The overall reaction in these artificial systems is water splitting to oxygen and hydrogen. Artificial water splitting can generally be divided into two half reactions, catalytic water oxidation and catalytic proton reduction. There is an increasing interest and demand to understand the detailed mechanism of these two key parts. Since DFT (density functional theory) in particular, has proven to be a powerful and popular tool in exploring reaction mechanisms, B3LYP and M06 functionals were employed to provide a theoretical explanation of these two important reactions in this thesis. For water oxidation reaction, many efficient Water Oxidation Catalysts (WOCs) based on Ru, Ir, etc., have been reported over the last several years. The discovery of mononuclear ruthenium WOCs carrying anionic ligands is one of the major breakthroughs recently. WOCs bearing anionic ligands are able to efficiently drive catalytic water oxidation with relatively higher Turnover Numbers (TON) and Turnover Frequencies (TOF). Therefore the influence of anionic ligands gained our attention. We decided to carry out a detailed investigation on this effect, and try to propose a full mechanism of this catalytic water oxidation as well. We found that 1) The anionic ligands exert a promoting influence on the ligand exchange between picoline and water, which facilitates the formation of aqua-Ru complex, 2) The anionic ligands facilitate the complex access to higher oxidation states, which is necessary for the OO bond formation, and 3) The work of OO bond formation is in progress. For the proton reduction reaction, the transport or movement of protons is vital and interesting in many biological and chemical processes, including the hydrogen uptake/production, the reduction of CO2 to formate, and the reduction of O2 to water. It is often related to energy storage and utilization. However, the details of these processes are still ambiguous. In most natural hydrogenase enzymes or synthetic catalysts based on iron or nickel, the incorporation of a pendant amine is a frequently occurring feature. This internal amine base seems to facilitate this proton transfer by acting as a proton relay. Our calculated results showed that the internal base allows for a splitting of one high enthalpy-high entropy barrier into two: one with a high enthalpy-low entropy barrier and the other with a low enthalpy-high entropy barrier, resulting in a low free energy of activation for proton transfer. Our results can serve as a guideline in the development of new catalysts, not only for proton reduction catalysts, but also for any process that involves proton transfer from a metal hydride to an external base, such as C-H activation and functionalization catalysts. A thorough understanding on the mechanism of water splitting can help generate a strategy to enhance the catalytic performance on both water oxidation and proton reduction. We can tune or modify the synthetic complex by accelerating the slow step (rate-determining step) in the overall catalytic cycle, and can construct artificial water splitting systems with improved performance. / <p>QC 20120920</p>

This thesis deals with two disjoint subdiciplines of quantum chemistry.  One isthe most used electronic structure method today, density functional theory(DFT), and the other one of the least used electronic structure methods,valence bond theory (VB).  The work on DFT is based on previous developments inthe department in density functional response theory and involves studies ofhyperfine coupling constants which are measured in electron paramagneticresonance experiments.  The method employed is a combination of arestricted-unrestriced approaches which allows for adequate description of spinpolarization without spin contamination, and spin-orbit corrections to accountfor heavy atom effects useing degenerate perturbation theory.  The work anvalence bond theory is a new theoretical approach to higher-order derivatives.The orbital derivatives are complicated by the fact that the wave functions areconstructed from determinants of non-orthogonal orbitals. An approach based onnon-orthogonal second-quantization in biorthogonal basis sets leads tostraightforward derivations without explicit references to overlap matrices.These formulas are relevant for future applications in time-dependent valencebond theory. / QC 20101006

A very important trend for studying biomolecules is computational chemistry. In particular, nowadays it is possible to use theoretical methods to figure out the catalytic mechanism of enzyme reactions. Quantum chemistry has become a powerful tool to achieve a description of biological processes in enzymes active sites and to model reaction mechanisms. The present thesis uses Density Functional Theory (DFT) to investigate catalytic mechanism of methyltransferase enzymes. Two enzymes were studied – Glycine N-MethylTransferase (GNMT) and Guanidinoacetate Methyltransferase (GAMT). Different models of the enzyme active sites, consisting of 20 to 100 atoms, are employed. The computed energetics are compared and are used to judge the feasibility of the reaction mechanisms under investigation. For the GNMT enzyme, the methyl transfer reaction was found to follow an SN2 reaction mechanism. The calculations demonstrate that the mechanism is thermodynamically reasonable. Based on the calculations it was concluded that hydrogen bonds to the amino group of the glycine substrate lower the reaction barrier, while hydrogen bonds to carboxylate group raise the barrier. In the GAMT enzyme the methyl transfer reaction was found to follow a concerted asynchronous mechanism which includes transfer of a methyl group accompanied by a proton transfer taking place simultaneously in the same kinetic step. The calculated barrier agrees well with the experimental rate constant. i / QC 20101124

<p>The present thesis is devoted to theoretical studies of light pulse propagation through different linear and nonlinear media. One dimensional holographic photonic crystals and one dimensional impurity band based photonic crystals are investigated as linear media. The effects of angular dependence of the band structures and pulse delay with respect to the light polarization are analyzed. A strict theory of nonlinear propagation of a few strong interacting light beams is presented and applied in the field of nonlinear optics. The key idea of this approach is a self-consistent solution of the nonlinear wave equation and the density matrix equations of the material beyond the so-called rotating wave approximation. The results of numerical studies led to a successful interpretation of recent experimental data [<i>Nature</i>, 415:767, 2002]. A theoretical study of the NO molecule by means of two-color infrared -- X-ray pump probe spectroscopy is presented. It was found that the phase of the infrared field strongly influences the trajectory of the nuclear wave packet, and hence, the X-ray spectrum. The dependence of the X-ray spectra on the delay time, the duration and the shape of the pulses are studied.</p>

The present thesis is devoted to theoretical studies of light pulse propagation through different linear and nonlinear media. One dimensional holographic photonic crystals and one dimensional impurity band based photonic crystals are investigated as linear media. The effects of angular dependence of the band structures and pulse delay with respect to the light polarization are analyzed. A strict theory of nonlinear propagation of a few strong interacting light beams is presented and applied in the field of nonlinear optics. The key idea of this approach is a self-consistent solution of the nonlinear wave equation and the density matrix equations of the material beyond the so-called rotating wave approximation. The results of numerical studies led to a successful interpretation of recent experimental data [Nature, 415:767, 2002]. A theoretical study of the NO molecule by means of two-color infrared -- X-ray pump probe spectroscopy is presented. It was found that the phase of the infrared field strongly influences the trajectory of the nuclear wave packet, and hence, the X-ray spectrum. The dependence of the X-ray spectra on the delay time, the duration and the shape of the pulses are studied. / QC 20101207

There is a growing need for synthetic bone graft materials, which is particularly apparent for procedures requiring impaction bone grafting (IBG), such as revision hip arthroplasty. Currently allograft bone is used that has limited supply and associated risks of transmission of infectious agents. Porous bioresorbable polymeric scaffolds can be created using supercritical carbon dioxide (scCO2). This thesis investigated the use of these scaffolds for impaction bone grafting procedures. Building on previous research within the literature poly(D,L-lactide) (PDLLA) and poly(D,L-lactide-co-glycolide) (PDLLGA) scaffolds of high molecular weight (100 kDa) were investigated for this use. Scaffolds were milled using a standard bone mill and impacted to create porous milled chips of bioresorbable scaffolds and impacted for mechanical shear testing and biocompatibilities. The impaction process used forces equivalent to those experienced during IBG. In vitro cell experiments were used to assess the proliferation and osteoblastic differentiation of mesenchymal stem cells (MSCs) on impacted scaffolds to identify the most promising scaffold compositions. These compositions included pure polymer and polymer:HA microparticle composites. Further experiments using animals (murine and ovine) were then used to investigate the in vivo performance of the scaffolds. A critical sized ovine femoral condyle defect established the osteoinductive and osteoconductive potentials of milled scCO2 foamed PDLLA + 10 wt.% hydroxyapatite (HA) microparticle scaffolds in vivo. The scale-up potential of scCO2 foaming of bioresorbable scaffolds was established using a 1 L vessel. Scaffolds scCO2 foamed using either a 60 ml autoclave or a 1 L vessel were characterised using scanning electron microscopy and micro computed tomography. Scaffolds from different batches were characterised and compared to ensure process repeatability was accounted for. The final chapter investigated differences in the osteoblastic differentiation of MSCs on PDLLA and PDLLGA scaffolds observed in experiments at the start of the study. Spincoated and dipcoated flat films of PDLLA, PDLLGA, and PDLLA:PDLLGA (50:50) were used for in vitro cell culture to remove the effect of morphological differences that affected scCO2 foamed scaffold experiments. Additionally, this chapter investigated the effect of the form of HA using HA nanoparticles andHA microparticles in scCO2 foamed PDLLA:HA composites for in vitro studies.