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Abstract: The present doctoral thesis examines the properties of carbon-based, porphyrin-based and hybrid carbon-porphyrin nanostructures as promising candidate materials for catalysis (including photocatalysis) applications. I use density functional theory simulations, together with experimental insights from collaborators, to both explain known behaviour and suggest ways in which these materials can be modified for improved catalytic efficiency. Since the catalytic activity of graphitic materials is concentrated on the edges, I investigate their properties in several ways. First, I attempt to understand the properties of folded edges of graphitic nanostructures and quantify their thermodynamic stability, and explain how the application of an electric field leads to their opening. Edge folding can reduce catalytic activity by allowing bond saturation at the edge, but at the same time they provide a way to achieve highly porous carbon-based materials, which could be very useful for catalytic applications. My calculations rationalise the experimental observations about these folded edges. Additionally, I investigate catalysts based on carbon- and iron-based nanostructures, in collaboration with experimentalists. I present models for N-doped graphitic/ferrihydrite nanocatalysts for CO2 reduction, and for Fe-N active sites in graphite-based catalysts. In contrast with carbon nanostructures, porphyrin nanostructures exhibit a welldefined band gap which makes them more useful in photocatalytic applications. In this thesis I explore possible routes to engineer the electronic properties of two types of porphyrin-based materials. The first type consists of fully-organic porphyrin nanostructures with various dimensionalities, and we show how the length of the linkers between porphyrin can be used to engineer their electronic band structures. The second type consists of two-dimensional (2D) porphyrin-based metal-organic frameworks, where we explored different strategies to optimise the photocatalytic behaviour, by changing metal centres, partially reducing the porphyrins or changing the bridges between the porphyrin units. Finally, I consider mixed graphitic/porphyrinic structures, based on the idea that such composites could combine the advantages of both types of structures, leading to superior photocatalytic behaviour. I discuss the adsorption of porphyrins on the surfaces or edges of graphene nanoribbon, and how the interaction affects the electronic properties of the combined structures. Overall, the thesis shows how computer simulation approaches can be used to understand, and also to design and optimise the electronic properties of carbon and porphyrin-based nanostructures to be applied in catalysis and photocatalysis.

Open Access

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Abstract: A series of modified solid polymethylaluminoxane (sMAO) catalyst supports have been developed for slurry phase ethylene polymerisation, using aryl di-ol modifier groups. Characterisation using ICP-MS analysis, X-ray total scattering, SEM–EDX, diffuse FT-IR and solid state NMR spectroscopy shows that the organic linker groups are uniformly distributed in a proposed organic framework stucture we call a “sMAOF”. When used as a support for rac-ethylene{bis(1-indenyl)} zirconium dichloride, (EBI)ZrCl2, these linker modified sMAOF materials provide a 40% enhancement in polymerisation activity with respect to unmodified sMAO: activities of 163 × 103 and 116 × 103 kgPE molZr−1 h−1 at 80 °C for (EBI)ZrCl2 supported on sMAOF(1,4-HO(C6F4)OH) and sMAO, respectively. The observed activity increase is correlated with the higher BET surface area and increased porosity in the linker modified sMAOF activating support.

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Abstract: Cu-BTC metal-organic framework (MOF) has been found to be a promising candidate for removing hazardous substances from air via adsorption1. To understand the role that the copper sites in Cu-BTC play in the adsorption process, we have performed a detailed X-ray absorption spectroscopy (XAS) study. Conventional XAS and high energy resolution fluorescence detection XAS (HERFD-XAS) were collected on degassed Cu-BTC, and after being exposed to CO2, water and benzene. The EXAFS analysis reveals that, although the local environment around the copper centers in all samples is similar, differences can be found in the first and second coordination shells. We have found that the Cu-O distance in the first coordination shell is slightly larger when the sample is immersed in water and benzene than in the degassed sample, while it does not change for the sample exposed to CO2. Small differences are also observed in the Cu-Cu distance, gradually increasing from 2.49 Å in the degassed sample, to 2.52 Å, 2.58 Å and 2.63 Å upon adsorption of CO2, benzene and water, respectively. HERFD-XAS has been used to obtain information about the electronic and geometric structure around the copper metal centers, as the use of high energy resolution enhances the features in the XANES spectrum enabling the detection of subtle changes2. We have observed differences in the intensity and the energy position of some of the XANES spectral features upon adsorption of different adsorbates that can be attributed to changes in the local environment around the copper centers, as detected in the EXAFS analysis. In this study we show that XAS is a powerful and very sensitive tool for studying host-guest interactions in MOFs, providing atomic-level insights into adsorption mechanisms.

Open Access

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Abstract: Post-synthetic modification (PSM) of the interpenetrated diamondoid metal-organic framework (Me 2 NH 2 )[In(BDC-NH 2 ) 2 ] (BDC-NH 2 = aminobenzenedicarboxylate) SHF-61 proceeds quantitatively in a single-crystal-to-single-crystal manner to yield the acetamide derivative (Me 2 NH 2 )[In(BDC-NHC(O)Me) 2 ] SHF-62 . Continuous breathing behaviour during activation/desolvation is retained upon PSM, but pore closing now leads to ring-flipping to avert steric clash of amide methyl groups of the modified ligands. This triggers a reduction in the amplitude of the breathing deformation in the two dimensions associated with pore diameter, but a large increase in the third dimension associated with pore length. The MOF is thereby converted from predominantly 2D breathing (in SHF-61 ) to a distinctly 3D breathing motion (in SHF-62 ) indicating a decoupling of the pore-width and pore-length breathing motions. These breathing motions have been mapped by a series of single-crystal diffraction studies.

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Abstract: Circumventing the impact of agrochemicals on aquatic environments has become a necessity for health and ecological reasons. Herein, we report the use of a family of five eco-friendly water-stable isoreticular metal–organic frameworks (MOFs), prepared from amino acids, as adsorbents for the removal of neonicotinoid insecticides (thiamethoxam, clothianidin, imidacloprid, acetamiprid, and thiacloprid) from water. Among them, the three MOFs containing thioether-based residues show remarkable removal efficiency. In particular, the novel multivariate MOF {SrIICuII6[(S,S)-methox]1.5[(S,S)-Mecysmox]1.50(OH)2(H2O)}·36H2O (5), featuring narrow functional channels decorated with both −CH2SCH3 and −CH2CH2SCH3 thioalkyl chains—from l-methionine and l-methylcysteine amino acid-derived ligands, respectively—stands out and exhibits the higher removal efficiency, being capable to capture 100% of acetamiprid and thiacloprid in a single capture step under dynamic solid-phase extraction conditions—less than 30 s. Such unusual combination of outstanding efficiency, high stability in environmental conditions, and low-cost straightforward synthesis in 5 places this material among the most attractive adsorbents reported for the removal of this type of contaminants.