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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Quantitative structural investigations of the water/metal oxide interface

Hussain, H. January 2014 (has links)
This thesis presents new findings that provide insight into the structural features of the adsorption of water on the TiO2(110), ZnO(10-10) and SrTiO3(001) surfaces. After exposing the TiO2(110)(1 x 1) surface to 1E6 mbar partial pressure of H2O for 3 h a (2 x 1) overlayer is produced as seen with STM. This overlayer was shown to lie in registry with the Ti5c rows. SXRD measurements show that every other surface Ti atom is occupied with an OH in atop position. The same average structure was found after exposing the surface to partial pressures of H2O and after the dipping the surface in 20 ml liquid H2O for 15 s. SXRD measurements were also collected for in-situ immersion of liquid. The results revealed the presence of a hydration layer. We found that adsorption of water from the residual produces a (1 x 1) structure consisting of a slightly shifted H2O/OH molecule on the ZnO (10-10) surface. After exposing the surface to a constant partial pressure of 5E7 mbar, a second water layer was detected with partial occupancy. Significant changes occurred when exposing the surface to 8 mbar partial pressure of H2O. The results revealed that the slightly shifted H2O/OH molecule displaces to a position that is atop of the surface Zn and the second water layer is now fully occupied. SXRD results demonstrate that the SrTiO3 (001) surface is mixed terminated with SrO and TiO2 layers and cover equally large areas. These layers are only partially occupied and leads to a surface coverage TiO2:SrO ratio of 68:32. When contacting this surface with a drop of water, the adsorption mode for the TiO2 terminated terrace is molecular in nature. On the other hand, for the SrO terminated terrace it appears that dissociation is the favoured adsorption mode.

Carboranes and their incorporation into siloxane polymers

Sugden, I. J. January 2014 (has links)
This is a report detailing the computational investigation of copolymers containing carborane and siloxane monomers, to aid in the design an industrially relevant material for use in high neutron radiative environments. This includes determining the optimal carborane/siloxane ratio in the designed material with regards to macroscale physical properties; with experimentally determined values for pure siloxane phases reproduced, using classical methods. The investigation shows that increasing carborane content increases bulk modulus and decreases the thermal expansion coefficient, levelling off beyond 50% carborane content. It also includes the effect of including specific side groups to polymer strands in order to affect properties; for instance, it is seen that phenyl groups increase the flexibility of the polymer strands. Alongside this, the report includes the simulation of property “aging”; using classical crosslinking methods to model the effect of high energy ions travelling through the material following neutron capture events, and ab initio simulation of damage to the monomer. Unsurprisingly, crosslinking sees a reduction in flexibility, leading to an increase in bulk modulus and a decrease in the thermal expansion coefficient, whilst the changes in vibrational spectra as a result of neutron capture events are predicted: due to changes in bond strength and orbital structure, modes involved with cage elements move to a higher frequency, and B-H modes move to lower. Finally for the designed material, context is given by examining the current state of the art: solid boron carbide, and its remarkable resistance to radiation of several different forms, with experimental theories and mechanisms discussed. Carborane clusters are further examined in other technological areas: thermal rearrangements of single carboranes and metallo-carboranes, with the 40 to 145 kJ/mol (dependent on mechanism) difference between theoretical and experimental activation energies rationalised, and investigations of icosahedral boron cluster anions in lithium battery electrolytes, where a ≈17% improvement in lithium mobility is theorised.

Porous carbon based solid adsorbents for carbon dioxide capture

Travis, W. January 2015 (has links)
The aim of this project is the design, synthesis and characterisation of porous carbon structures capable of the selective capture of carbon dioxide (CO2) from the exhaust gases of coal and gas post-combustion power stations. In such systems, the fossil fuel is burnt in an air environment producing CO2 as just one of a multi-component flue gas. This flue gas is expected to contain nitrogen and water among other constituents. It is at ambient pressures and temperatures of ≥323 K. Successful capture materials should have highly microporous structures, rapid sorption kinetics and be capable of repeated sorption/desorption cycles. To develop highly microporous carbon sorbents a range of porous materials have been synthesised using chemical and physical activation of precursors obtained through top down and bottom up approaches. Porosity has also been achieved in precursors through the controlled use of graphene exfoliation, melamine-formaldehyde resin aerogel formation, soft templates, controlled carbonisation and synthesis of microporous organic polymers. The role of nitrogen dopants (N-dopants) within the CO2 sorbent materials has also been investigated. To increase understanding and tune the sorbents performance, porous carbon structures have been synthesized containing: pyridine, pyrrole, quaternary and triazine nitrogen groups. Characterisation was achieved using Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, nuclear magnetic resonance spectroscopy, transmission electron microscopy X-ray diffraction, thermogravimetric analysis and nitrogen (N2) isotherms at 77 K. CO2 sorption analysis was carried out using volumetric and gravimetric analysis. The influence of N-dopants on the adsorbate-adsorbent interaction is characterised using CO2 volumetric isotherms, isosteric heats of adsorption and CO2/N2 selectivity analysis.

Engineering carbon-based porous materials from selected precursors for high-capacity CO2 capture

Zhu, B. January 2015 (has links)
The mitigation of climate change is one of the major global challenges in the 21st Century. Carbon capture and storage (CCS) is a promising technology to effectively reduce anthropogenic CO2 emissions into the Earth’s atmosphere. There are various candidate materials for CO2 capture but each has its own advatanges and disadvantages. Carbon-based materials are of low-cost and have relatively high cyclicity for CO2 and its porous structure and surface functional groups can be tailored to improve CO2 capture performance. Effective but low-cost carbon precursors need to be explored for potential mass production in the furture. This research aims to explore various polymeric, biomass and graphitic materials as the precursors for the development of effecive carbon sobents for CO2 capture. In addition, the influence of porous structures and chemical dopants on CO2 sorption are also experimentally studied in relation to the porosities and surface chemistry of the sorbents. Five distinct synthesis approaches are explored comparatively to determine the potential of polymeric, biomass and graphitic materials as precursors for effective carbon sorbents. These approaches include a novel method of producing millimetre-sized carbon spheres from poly(acrylonitrile-co-acrylamide)/DMSO solution, chemical activation of London Plane leaves, spruce pine cones and graphite oxide, and ball-milling of graphite. The work on the polymer-derived carbon spheres produced desirable carbon macro-spheres with radially channelled and hierarchically porous structures, via a “one-pot” solvent exchange process. The structure shows excellent CO2 capacity of 16.7 wt% at 25 °C and under 1 bar CO2, enhanced by rich nitrogen doping and microporosities. The biomass-derived carbon sorbents further clarify the influence of metal-dopants, inherited from the biomass precursors, on CO2 adsorption. It was noted that besides nitrogen dopant and ultramicropores (<0.7 nm), residual calcium and magnesium in biomass-derived carbon also enhanced CO2 adsorption on carbon sorbents. The CO2 uptake of a pine cone-derived carbon sorbent (20.9 wt%) has matched the highest CO2 uptake (21.2 wt%) reported in the literature at 25 °C and under 1 bar CO2, though the latter has a relatively large ultramicropore volume. To further clarify the influence of microporous structure and chemical dopants on CO2 uptake, graphite oxide (GO) and ball-milled graphite (BG) were studied as graphitic precursors as these have known chemical structures and their resulting sorbents contain no other chemical dopants. The characterisation results show chemical activation with potassium hydroxide can develop a similar porous structure in GO- and BG-derived carbon, compared with those of polymer- and biomass- derived carbon. However, the former show comparatively lower CO2 capture capacities under the same test conditions (25 °C and 1 bar CO2), which is believed to be due to less well-developed ultramicroporous structure and the absence of chemical dopants. Based on the present experimental data, further analysis reveals that there is a difference between specific surface area calculated by the Brunauer-Emmett-Teller (BET) equation and the Density Functional Theory (DFT) model. The cause of this is the intrinsic difference in the method of calculation, where the BET equation assumes a flat and homogeneous surface, while the DFT model takes the pore shape into consideration. Furthermore, both CO2 uptake and specific CO2 uptake (CO2 uptake/porosity) are plotted against three porosity parameters, namely BET surface area, total pore volume and ultramicropore volume. The plots show those samples with higher nitrogen and metal contents exihibit higher specific CO2 uptakes. To extend the interpretation of results, an Artificial Neural Network (ANN) is adopted as a simulation tool to study the influence of ultramicropore, nitrogen and metal dopants on CO2 uptake. Characteristic results from both the present work and the literature are used as the input data for the simulation. The simulated results show CO2 uptake increases considerably with increasing ultramicropore volume and metal content. However, the nitrogen content has relatively limited influence, compared with the former two, contrary to common belief. Finally, several future lines of work are proposed to further improve the performance of the materials. For the synthesis of carbon spheres, DMSO can be added into the water bath to slow the solvent exchange process. As a result, the macroporous strucure of the sphere can be modified to enhance its mechanical strength. For the study on the biomass-derived carbon, several other leaves can also be used as carbon precursors. The porosities, chemical compositions and CO2 uptakes of the cabon sorbents derived from these leaves can be compared with those of the London Plane leaf-derived carbon, to further clarify the influence of the biological structures and chemical properties of biomass precursors on the resulting carbon. For the work on ANN, the simulation is limited by the available experimental data for metal-doped carbon. The accuracy of prediction by ANN can be further improved when more experimental data are reported in the literature and used for training the network.

Polymersomes mediated intracellular delivery of antibodies : implication in anticancer therapy

Chierico, L. January 2015 (has links)
Cancer is one of the leading causes of death in the developed world. Nevertheless, many pharmaceutical products available in the clinic lack of tissue specificity, and often have severe side effects. Nowadays, advances in molecular biology and biotechnology have allowed the development of biological therapeutic approaches aimed to give a step forward on cancer treatment. Biotherapy involves the use of biomolecules such as antibodies that have the potential to increase the specificity of anticancer treatments, thus limiting the side effects. Unfortunately, the effectiveness of such biomolecules is hindered by their pharmacokinetics, and their translation into patient care is heavily restricted by low solubility in water, instability/degradation in vivo and low efficiency. Besides that, such biomolecules require appropriate delivery strategies to penetrate cellular barriers, thus being able to interfere with pathways that can be involved in cancer development. This research project aims to bridge the lack of technology regarding the development of an effective and biocompatible delivery system. The pH sensitive PMPC-PDPA ((poly(2-(methacryloyloxy)ethyl phosphorylcholine) - poly(2-(diisopropylamino)ethyl methacrylate)) polymersome was employed as candidate for the intracellular delivery of functional therapeutic antibodies in live cells. The PMPC-PDPA diblock copolymer combines the ability to release the loaded cargo upon acidification within the endosomes with an overall biocompatibility. First, the antifouling proprieties of polymersomes were investigated, and then compared to micelles. Subsequently, electroporation was exploited as reliable technique to effectively encapsulate antibodies within polymersomes. The delivery of antibodies in live cells was assessed using anti γ-tubulin antibody as a model system. Finally, Ki-67 was explored as a possible target for anticancer therapy. Interestingly, relevant differences in the biological functions of this marker were revealed between cancerous and non-cancerous cells. Furthermore, antibodies against Ki-67 were delivered in live cells, and their activity was tested to explore the potential of Ki-67 as a target for anticancer therapy.

The binding of glycosaminoglycans to calcium minerals : implications for crystal growth

Ruiz Hernandez, S. E. January 2015 (has links)
This thesis presents the results of classical molecular dynamics simulations (MD) of the adsorption of the glycosaminoglycan chondroitin 4-sulfate (Ch4S) on two of the inorganic components of kidney stones: hydroxyapatite and calcium oxalate monohydrate. First, MD has been employed to study the interactions of the two saccharides of Ch4S with two important (0001) and (01-10) surfaces of hydroxyapatite in the presence of solvent. MD simulations of the mineral surfaces and the saccharides in the presence of solvent water allows the calculation of the adsorption energies of the saccharides on the HAP surfaces, and reveals detailed information about the interacting groups and solvent effects. A similar analysis is carried out using a dimer of Ch4S with the three relevant (100), (010) and (12-1) calcium oxalate monohydrate surfaces, after a reliable set of potential parameters is derived and carefully tested assuring it is indeed able to reproduce the crystal geometries and properties. Additionally, it allows the creation and relaxation of multiple surfaces to construct the theoretical equilibrium morphology resembling the one found in the experiment. A study of the influence of background ions in solution on the reactivity of the surfaces of calcium oxalate monohydrate is initiated.

Spectroscopy and dynamics of fluorescent protein chromophore anions

Mooney, C. January 2015 (has links)
Gas-phase photoelectron imaging spectroscopy has been combined with electrospray ionisation to examine the electronic structure and dynamics of a variety of biologically relevant chromophores. Both nanosecond and femtosecond spectroscopy techniques have been employed and many of these experimental measurements have been complimented by ab initio calculations. The photodetachment spectra of model chromophore anions of Green Fluorescent Protein (GFP) and Cyan Fluorescent Protein (CFP) along with their constituent moieties, phenol and indole, have been recorded at 269 nm and 330 nm. This study provided measurements of the vertical and adiabatic detachment energies of the ground and first excited state radicals of all four molecules. A detailed nanosecond photoelectron spectroscopy study of the GFP model chromophore anion was then undertaken using a range of wavelengths between 315 nm and 328 nm. This has revealed the interplay between direct and indirect detachment processes and their influence on the photoelectron spectra. A femtosecond time-resolved study of the model GFP chromophore anion was also performed along with ab initio calculations to identify key molecular structures. This study revealed that the ultrafast decay dynamics of the gas-phase model anion have similar timescales as those measured in solution. In another study, photodetachment spectra of chemically modified GFP model chromophore anions were measured at 350 nm. The addition of strongly electron donating or withdrawing groups on the phenoxide moiety of the chromophore demonstrates how chemistry can be exploited to tune the electron emission properties the chromophore. Finally, a study of model chromophore anions of Photoactive Yellow Protein (PYP) was undertaken. This work examined the photoelectron spectra of three isomers of the PYP model chromophore at a wide variety of wavelengths between 315 nm and 364 nm. The vibrationally resolved spectra allow us to identify the predominate anion isomer produced by electrospray ionisation and highlights the importance of direct and indirect photodetachment pathways in anion spectroscopy.

Computational studies of FeS : bulk, surfaces and clusters

Haider, S. G. January 2014 (has links)
In this thesis we present the results of our simulation studies of iron sulphide minerals, with focus on bulk, surface and cluster chemistry. DFT+U calculations were employed to study the mineral greigite (Fe3S4), which has important implications in Origin of Life theories. Using a combination of DFT and Monte Carlo methods, we were able to explore the probable cation distribution of Ni-doped greigite over the two available lattice sites (tetrahedral and octahedral) at varying concentrations, as well as calculate the enthalpy of mixing and thus deduce at what concentration of Ni this mineral would be most stable. Results showed that within the lattice, site occupation by Ni will be concentration-dependent, whilst violarite, FeNi2S4, is likely to be the most stable (Fe,Ni)S phase. The (001), (011), and (111) surfaces of violarite, both naked and in the presence of water, were investigated next, using a combination of DFT-D2+U methods. The (001) was found to be the most stable surface, whilst the (011) the most reactive with respect to water. The adsorption and dissociation of water on the surfaces also revealed a synergistic effect, whereby the adsorption of one water has a conducive effect on the adsorption of the next. CPMD simulations were then conducted on the following hydrated ions: Fe2+, Fe3+ and S2-, and on the following systems, FexSy (x,y≤ 4), to investigate the structural and dynamical properties in water. Calculation of the Gibbs free energies (ΔGaq) revealed that the formation of FexSy clusters with x,y ≤2 will not only be in competition with the formation of iron hydroxides, but is also temperature-dependent.

Studies of atomic and molecular cations

Fletcher, James January 2014 (has links)
Atomic and molecular cations have the potential to strongly influence a number of industrial, atmospheric and interstellar environments in which they are expected to be present. As a result, information on the generation and reactivity of positively charged species is invaluable when attempting to model and understand the physical and chemical processes taking place in such surroundings. This thesis reports a number of experimental investigations of the formation and reactivity of atomic and molecular cations. Firstly, a detailed study of the electron ionisation of sulphur dioxide (SO2) is presented. Relative precursor-specific partial ionisation cross sections for the fragment ions formed following electron ionisation of sulphur dioxide have been measured using time-of-flight mass spectrometry coupled with ion coincidence detection. These data quantify, for the first time, the formation of all fragment ions, relative to the formation of SO2+, via single, double and triple electron ionization of SO2. Secondly, the investigations of the bimolecular reactivity of a number of doubly (I2+ and N22+) and triply charged (I3+, Xe3+, CS23+) reactants are presented. A crossed-beam mass spectrometer was used to identify ion-molecule reaction products. The doubly and triply charged (I2+ and I3+/Xe3+) reactants are shown to participate in processes involving substantial rearrangement of chemical bonds. This reactivity can be encapsulated using a simple electrostatic model and energetic arguments. Furthermore, the same model has been updated to account for the results observed following the reactions of atomic trications. A different mass spectrometer, equipped with a position-sensitive coincidence ion detector, was then used to explore the dynamics of reactions involving first a molecular dication (N22+) with various low-mass organic molecules and then atomic (Xe3+) and molecular trications (CS23+). Product ion velocities determined using this technique can be used to explore the reaction energetics and angular scattering distributions for individual ion-molecule reaction channels. In turn, the interpretation of these data allow the identification of reaction mechanisms. The range of reactions exhibited in all of these studies is surprisingly diverse, clearly indicating a complex chemistry for collision systems involving dicationic and tricationic reactants.

Hydroacylation of N=N bonds via aerobic C-H activation of aldehydes, and reactions of the products thereof

Akhbar, A. R. January 2014 (has links)
The development of methods to construct new chemical bonds efficiently and selectively whilst minimising energy usage and waste production is of high importance in organic chemistry. Many current methods employ inefficient, costly and often toxic multi step protocols to generate new chemical bonds. The hydroacylation reaction is one method of reducing such inefficiencies. The development of an aerobic hydroacylation protocol in the Caddick group has recently allowed the functionalisation of aldehydes with a wide array of electron deficient alkenes. This process relies on trapping an acyl radical intermediate, from the auto-oxidation of aldehydes to acids, with a suitable alkene. Since aldehyde auto-oxidation takes place readily in the presence of atmospheric oxygen, the aerobic hydroacylation reaction can be conducted in aqueous media in the absence of any additional reagents. Following on from previous work in the group, this thesis describes studies towards expanding the scope of this novel methodology in the formation of C-N bonds. It also assesses the scalability of this reaction in order to make acyl hydrazides for further chemical transformations; as such, the development of protocols for the conversion of acyl hydrazides to carboxylic acid derivatives and to ketones will also be described. Chapter 1 provides an introduction to and a general overview of current methods of hydroacylation and acid derivative syntheses. Chapter 2 describes the development of conditions for, and application of aerobic hydroacylation towards C N bond formation, and the scalability of the hydroacylation reaction. Chapter 3 will focus on solving the failures of previous attempts for the conversion of acyl hydrazides to tertiary amides. Chapter 4 will demonstrate the applicability of acyl hydrazides to the synthesis of carboxylic esters and describe some of its limitations. Finally, chapter 5 will reveal acyl hydrazides as a new class of precursors for the chemoselective synthesis of ketones.

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