This thesis studies the electrostatic interactions of ions in solution. This is a well studied but counter-intuitive field with many behaviours which defy conventional theoretical results, mainly as a result of the complexity of modelling the ions and the surrounding systems. Therefore this work endeavours to simplify the theoretical environment by considering ions under purely Coulombic interactions. A further simplification of this model is to consider the ions to be completely penetrable or ’ultrasoft’, i.e. the ions can pass through one another, this reduces the complexity of dealing with the excluded volume associated with the non-penetrable or ’hard core’ ions. This ’ultrasoft’ model is studied using both a variational mean field theory and a virial expansion in the first place and compared to integral equation methods such as the random phase approximation and the Hyper-netted chain theory as well as Monte Carlo (MC) simulations from the available literature. Then molecular dynamics simulations are used to test the model in various situations. The two main systems studied under this model are a symmetric electrolyte consisting of penetrable cations and anions with identical size and charge to one another,and an asymmetric electrolyte consisting of ultrasoft cations and point-charge anions. The Ultrasoft model requires a charge distribution to be defined within the theory, this work has examined both a Bessel and a Gaussian charge distribution for each of the symmetric and asymmetric cases. The symmetric model shows good agreement with MC simulations from the literature which allows for more extreme temperatures and densities to be studied. This study reveals like charged clustering at the low temperature-high density limit. The asymmetric model shows analogies with the classical one component plasma as the temperature of the system is decreased and the density is increased. The asymmetric model also shows clustering but it takes a different form to the symmetric electrolyte.

The post-synthetic modification of CPO-27(Mg) by introducing nickel cations into the framework is described. A combination of surface sensitive XPS analysis, synchrotron powder X-ray diffraction and selected area and bulk EDX measurements revealed the distribution of Ni²⁺ throughout the crystal with the highest concentration towards the external surface forming a nickel-rich rim. By adding nickel acetate and chloride salts in combination with a weak acid, Ni²⁺ contents of up to 67% for the bulk material were achieved via a one-pot preparative procedure. A combined mechanism of overgrowth and isomorphous cation exchange is proposed. The study led to an improvement of porosity to N₂ (77 K) up to 17 mmol g⁻¹, close to values achieved elsewhere via complex activation procedures. High values for the adsorption of carbon dioxide of up to 6.7 mmol g⁻¹ at temperatures and partial pressure relevant for carbon capture from post-combustion power plants were accomplished (298 K, 0.1 bar) and were shown to be repeatable over cycles under dry conditions. The synthesis, structure and adsorption properties of a series of zinc imidazolate zeolitic imidazolate framework, ZIF, materials was also investigated. Structural details of the zinc nitroimidazolate ZIF-65(Zn) were determined by Rietveld refinement. Heating experiments of as prepared ZIF-65(Zn) revealed a partial transformation from a cubic framework to an unknown structure, shown to be reversible. The new phase possess high porosity to nitrogen and showed stepped, hysteretic adsorption and desorption isotherms for at 77 K and CO₂ at 298 K. Using methanol instead of DMF in synthesis yielded a novel dense non-porous zinc nitro imidazolate structure. A series of novel structures was prepared via synthesis including a mixture of 2- nitroimidazole (NIm) and purine with different zinc metal sources. Two MOF structures were found to consist of purine linkers only, but could not be rendered porous. By changing the metal source or solvent an isoreticular structure of the ZIF- 68 (GME) family was obtained, composed of purine and NIm, as well as a novel form of a mixed linker ZIF with the RHO topology with Im-3m symmetry that exhibits large pores and exo-Zn and exo-NIm moieties decorating the cavity walls. The nitrogen uptake (77 K) of 6.5 mmol g⁻¹could be increased to 12.5 mmol g⁻¹ by removing exo-moieties through water washing. The use of a diamino functionalised purine linker (DAP) together with NIm gave a new ZIF material, STA-17, with a novel topology. The structure was found to exhibit porosity to nitrogen (77 K) of 6.5 mmol g⁻¹ and carbon dioxide at (198 K) of 5 mmol g⁻¹, but shows weak interaction with CO₂ at 298 K. Indexing from synchrotron powder XRD data gave a hexagonal unit cell with a = b = 29.725 Å and c = 18.606 Å. Subsequent analysis of the composition using NMR, TGA and IR techniques revealed the presence of both linkers in the structure and a linker ratio of 2:1 (NIm : DAP). Although crystals of suitable quality for single crystal X-ray diffraction were not obtained, a partial model for the structure is proposed via analogy with a hypothetical zeolite structure and analysis of powder X-ray diffraction data.

Bicontinuous cubic phases are high surface area nanostructures formed spontaneously by amphiphilic lipids on contact with water. This thesis reports studies into the behaviour of thin lipid films, capable of forming bicontinuous cubic phases, and their use as soft templates for the electrodeposition of aligned platinum nanostructures. In addition, the suitability of these mesoporous films for use as catalysts in direct alcohol fuel cells is detailed. Through an experimental and theoretical study of thin films of lipid under controlled humidity, it was demonstrated that adding glycerol progressively lowers the humidity at which QII phase films are stable, without affecting their lattice parameter. These findings open up the possibility of utilising cubic phases in a much wider range of environments, where typically the structure would collapse due to dehydration. The addition of glycerol allowed for a study into the orientation adopted by these lipid films; the QIIG and the QIID phases were observed to be reproducibly orientated with the (110) and the (111) facets aligned parallel to the substrate respectively up to a measured thickness of 1.4 µm. These results agreed with theoretical predictions based on the minimization of interfacial energy. Self-assembled cubic phase films were used to template mesoporous platinum nanostructures 1-2 microns thick featuring uniaxial alignment with the (111) plane orientated parallel to the substrate and high surface area (42 ± 1 m2 /g). To investigate the electrodeposition process time resolved X-ray scattering measurements were taken in situ as the platinum nanostructures grew within the lipid template using a custom electrochemical cell developed for use on a synchrotron beamline. These measurements identified two surprising characteristics of the templated electrodeposition process. Firstly, the aligned platinum nanostructures are templated from polydomain lipid films, suggest that up to 3 µm away from the lipid/substrate interface, polydomain QII samples display a region of uniaxial orientation. Secondly, the platinum films are found to be cubic while the lipid template is in place but undergo a slight distortion of the lattice along the 111 direction once the template is removed resulting in a rhombohedral structure where α = 87 ˚ (α = 90˚ for cubic structures). Additionally, these phytantriol templated platinum nanostructures were assessed for use as anode catalysts in alcohol fuel cells. The catalytic response towards the oxidation of methanol and ethanol was found to be enhanced in phytantrioldirected nanostructured films in comparison to non-structured platinum. Lipid templated platinum was directly electrodeposited onto porous carbon gas diffusion layers as used in conventional fuel cell design. Platinum nanostructures on carbon and gold disc electrodes showed a comparable result towards the oxidation of ethanol. These findings present lipid templated electrodeposition as a practical method to incorporate nanostructured platinum materials into conventional fuel cell designs for enhanced catalytic response towards the oxidation of alcohols.

In this thesis, a combination of computational techniques, namely periodic ab-initio QM methods, and interatomic potentials (IP) have been applied to study metal substituted aluminophosphate (MeAlPOs) catalysts. This computational study has focused on the following topics: (1) The structural, electronic, acid and redox properties of substitutional dopants in AlPO frameworks: The heteroatoms investigated include Mg2+, B3+, Cr2+/3+,Fe2+/3+, Co2+/3+ Ni2+, Ca2+, Ga2 and Sr2. Structural data for the defect centres are in agreement with the available experimental data obtained by in situ EXAFS studies. The calculated energetic results, which include the substitutional and redox energies of the dopant ions, are able to rationalise the experimental evidence concerning the framework instability at high metal loading, and the redox activity during catalytic cycles. Results suggest that among the transition metal ions investigated, Fe is the most stable in the 3+ oxidation state, while Mn is the most stable as the 2+ ion. The acid strength is due to a complex combination of the structural and electronic features of the dopant ion, and does not show appreciable correlation with the local environment or electronic properties of the metal dopant in the framework. (2) Site ordering of trivalent substitutional ions in AIPOs: Results show that the size of 3+ metal dopants has a major influence upon their site ordering in AlPO frameworks. Bigger metal dopants prefer to substitute 'free' A1 sites, located in unconstrained regions of the framework, whereas small metal dopants are energetically stable when replacing A1 sites situated in smaller cages. This site preference increases on increasing the size difference between host ion (Al3+) and dopant, and is explained via the topological features of the host AlPO framework. (3) Hydration in MeAlPO-34 catalysts Upon hydration, the presence of a metal dopant in the AlPO framework activates the framework towards hydration. Substitutional Me3+ ion interacts preferentially with water molecules; the adsorbed water is energetically stable when coordinated to the heteroatom rather than the framework A1 species. This indicates that the Me3+ dopant is a better Lewis acid than framework aluminium. In divalent metal doped AlPO-34 framework, the dopant is screened by the acid OH group from direct interaction with the adsorbed water. The water-dopant Lewis interaction is from the region behind the Bronsted acid site. The stable adsorption site in the Me2+ doped AlPO-34 is the acid proton, which forms a strong hydrogen bond with the water oxygen. The Me -OH substitutional defect activates the framework A1 ions towards hydration, in particular the A1 ion located opposite to the Me2+ dopant and in the same cage containing the defect. The latter result is important to explain the low resistance of AIPOs and MeAlPOs to steaming and chemical treatment at high temperature, which may limit their applicability in heterogeneous catalysis compared to zeolites.

This thesis presents the results of ab initio based simulation studies of magnetite (Fe₃O₄) and related FeM₂X₄ (thio)spinels with M = Cr, Mn, Fe, Co and Ni and X = O and S. Using density functional theory with long-range dispersion correction and on-site Coulomb interactions (DFT + U – D2), we have investigated a number of properties of these materials. Firstly, we present a study of the inversion degree and its relevance in the electronic structure and magnetic properties of the spin filter candidates FeM₂X₄, which are one of the key devices in spintronic applications. We also analyze the role played by the size of the ions and by the crystal field stabilization effects in determining the equilibrium inversion degree. Secondly, we present the calculations of the elastic constants and other macroscopic mechanical properties by applying elastic strains on the unit cell of Fe₃O₄, which is the main component in different types of catalysts used in myriad of industrial processes. Thirdly, we calculate the geometries and surface free energies of a number of Fe₃O₄ surfaces at different compositions, including the non-dipolar stoichiometric plane, and those with a deficiency or excess of oxygen atoms. We propose a morphology in thermodynamic equilibrium conditions for the nanocrystals of this compound. We also present the simulated scanning tunnelling microscopy images of the different terminations of the surfaces shown on the Fe₃O₄ morphology. Finally, we investigate the initial oxidation stages of the greigite (Fe₃S₄) (001) surface induced by water. Fe₃S₄ is a mineral widely identified in anoxic aquatic environments and certain soils, which can be oxidised by these environments producing and extremely acid solution of sulfur-rich wastewater called acid mine drainage (AMD). We propose a number of mechanisms involving one or two water molecules and one OH group to explain the replacement of one sulfur by one oxygen atom in this mineral. The findings presented in this thesis provides a theoretical insight into various bulk and surface properties of this group of compounds.

No description available.

The formation of aromatic carbon to nitrogen bonds is one of the most important processes used in the chemical industry. It is prevalent in many biologically-relevant molecules such as pharmaceuticals and agrochemicals. A modified Hofmann-Löffler-Freytag reaction, which allowed the direct functionalisation of aromatic C-H bonds using N-haloamines under UV-irradiation in highly acidic media, was first reported by Bock et al. in 1965.1 The reported conditions used concentrated sulfuric acid as solvent and demonstrated a minimal substrate scope. Here, it has been shown that UV-irradiation of N-chloroamines with 10 equivalents of methanesulfonic acid in DCM allows for the intramolecular amination of unfunctionalised aryl C-H bonds to form tetrahydroquinolines. These novel conditions have been extended to 30 examples including in a concise synthesis of the alkaloid natural product angustureine. Furthermore, studies have helped elucidate a potential mechanism of the reaction and led to the discovery of a 1,2-alkyl migration reaction. The reaction has also been shown to work in a continuous photochemical reactor. This was extended to work in a two-stage reactor where amines were chlorinated and reacted in situ to form tetrahydroquinolines directly. Some of the substrates produced with the photochemical methodology have been tested in enzymatic deracemizations using genetically modified monoamine oxidase enzymes. Whilst modest activity was observed for a series of N-substituted tetrahydroquinolines, a group of natural products containing N-unsubstituted tetrahydroquinoline cores were successfully deracemized, with ee’s as high as 90% obtained.

The work presented in this thesis utilises the HIRAC chamber for the development and characterisation of instrumentation for measurements of OH and HO₂ radicals, and OH reactivity. This instrumentation is implemented, alongside other standard measurements, following oxidation of processes of butanol, a potential biofuel, focussing on OH reactivity and ozone formation. Results from further development of calibration methods for determining the sensitivity of a FAGE instrument are presented.

1,2-Diols and 1,2-ketoalcohols are important functional groups that can require multiple steps to synthesise, which increases yield losses, waste and often uses stoichiometric reagents and toxic/expensive catalysts. The ability to transform simple substrates into more complex products in one-pot with two or more catalysed steps is desirable, especially if a single catalyst can carry out both reactions. A multifunctional catalyst system was designed to transform primary alcohols into 1,2-diols through three sequential catalysed transformations; transfer dehydrogenation, benzoin condensation, and transfer hydrogenation. Two families of novel ligands and iridium(III) complexes bearing either thiazole or triazole rings were synthesised towards creating a multifunctional catalyst and characterised using mass spectrometry, NMR spectroscopy and x-ray crystallography. During the synthesis of the ligands, the alkylation of thiazole compounds and the DIBAL-H reduction of a thiazole ester were developed. The organo-organometallic complexes were tested for the transfer dehydrogenation of benzyl alcohol and the reaction was investigated to show that the equilibrium between the forward and reverse reaction, and not catalyst deactivation, was the cause of limited conversion. The hydrogen acceptor was varied and acetone was found to be the most effective when used as a dilute solvent with strictly inert reaction conditions, reaching up to 78% conversion. Four of the novel complexes gave comparable conversions to the control catalyst; however, the benzoin condensation reaction was not successful. The transfer hydrogenation of benzaldehyde was tested and found give quantitative conversions with the majority of novel complexes. A substrate scope identified that the more electron rich substrates were more easily oxidised. With a secondary alcohol, the transfer dehydrogenations occurred at a faster rate compared to the primary alcohol, reaching quantitative conversion.

No description available.