School of Chemistry - Theses
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ItemMesoporous Ti-based nanomaterials for photocatalysis and energy storage( 2017)Inspired by the discovery of the photocatalytic phenomenon in splitting water, enormous efforts have been devoted to the research of TiO2 materials. This has led to various applications ranging from photovoltaics and photocatalysis to batteries and sensors, which can be roughly divided into ‘energy’ and ‘environmental’ categories. In general, the effectiveness in the practical applications depend not only on the intrinsic properties of the TiO2 material, but also on modification to the material, including composition, morphology, and the compositional modification. As a photocatalyst, TiO2 is a wide band gap semiconductor (3.0-3.2 eV) that can be used to decompose organic compounds under ultraviolet light irradiation. An efficient strategy to extend the light response to the visible range and thus improve photocatalytic activity is by designing a heterojunction semiconductor. In this thesis pristine anatase TiO2 microspheres were used to prepare mesoporous TiO2/g-C3N4 microspheres via a nano-coating procedure followed by calcination, where the porous TiO2 acts as the active supporting scaffold and g-C3N4 as the visible light sensitizer. The composite microspheres were 8.5 folds more active in degrading phenol under visible light irradiation than mesoporous g-C3N4. Furthermore, starting with mesoporous TiO2 hollow microspheres, mesoporous brookite/anatase TiO2/g-C3N4 hollow microspheres were prepared via a facile nanocoating procedure that showed mixed phases of brookite (48 %), anatase (44 %), and rutile (8 %), incorporated with a g-C3N4 coating layer. The mesoporous hollow microspheres exhibited a unique hollow shell morphology of packed TiO2/g-C3N4 nanosheets, and a remarkable 5-fold increase in degrading phenol under visible light irradiation compared to mesoporous g-C3N4. Besides visible light photocatalysis, TiO2 can be used as an anode material for lithium-ion batteries, as it shows good gravimetric performance (336 mAh g-1) and excellent cyclability. To overcome the poor rate behaviour, slow lithium-ion diffusion, and high irreversible capacity decay, TiO2 nanomaterials with tuned compositions and morphologies are being investigated. Here, a promising TiO2 material has been prepared that comprises a mesoporous ‘yolk-shell’ spherical morphology in which the core is anatase TiO2 and the shell is TiO2(B). The electrochemical results indicate high specific reversible capacity at moderate current (330.0 mAh g-1) and cyclability (98 % capacity retention after 500 cycles). Lithium-sulphur batteries have attracted considerable attention as they have high specific capacity (1675 mAh g-1) and the abundance of sulphur, makes them one of the more promising next-generation battery technologies. However, commercialization of LSBs has generally been hampered by low sulphur utilization and poor long-term cyclability. These issues can be addressed, in part, by producing cathodic additives to encapsulate sulphur and polysulphides during the charge/discharge process. Mesoporous Magnéli Ti4O7 microspheres were prepared via an in-situ carbothermal reduction that exhibited large pore volume (0.39 cm3 g-1) and high surface area (197.2 m2 g-1). Strong chemical bonding of the polysulphides to Ti4O7, along with effective physical trapping in the mesopores and voids of the matrix, give superior reversible capacity (1317.6 mAh g-1) and cyclability (88 % capacity retention after 400 cycles). Ti-based materials with carefully tuned compositions, porosity, and morphologies have been constructed and tested in photocatalytic and energy storage applications revealing promising potential.