The photocatalytic properties of titanium dioxide have been widely studied over recent decades since the discovery in 1972 of water photolysis by TiO2 electrodes. There are a number of different TiO2 polymorphs. Rutile and anatase are the most studied due to their chemo-physical properties. Under ultraviolet light, TiO2 is able to absorb photons, creating a charge separation on the surface, an electron and a positive “hole”. This electron-hole pair then reacts with water and oxygen, generating radicals, very unstable and reactive species which show great potential for neutralisation of pollutants. In the introduction the state of art of photocatalysis; chemo-physical principles, applications and current analysis are described. A number of protocols to test photoactivity are discussed with particular emphasis on the importance of gas phase reactions. The development of a novel system to study gas phase reactions by mass spectrometry was explored, detailing the conditions and parameters that were optimised. This instrument was used to analyse photocatalytic properties of TiO2 powders and photocatalytic coatings under different UV light conditions. The results showed how TiO2 in the form of anatase and rutile removed nitrogen and carbon dioxide under different UV light sources, with anatase being more effective. A comprehensive study of several commercially available TiO2 powders and coatings was performed to identify the differences between photocatalytic properties, using electron microscopy, Raman and UV-vis diffusive spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. An important question that was answered in this thesis is whether the physical properties of nanoparticles or their electronic properties are critical for their photocatalytic behaviour. Results for anatase powders of different particle size and surface area showed how the positioning of their electronic band gap with the wavelength of the UV light source was fundamental for an effective photocatalyic process. In order to improve the photocatalytic process, “self-doping” TiO2 was investigated. Different reduction temperatures were studied to generate the best ratio of Ti3+-Ti4+ that stabilised the charge distribution process to maximize the electron-hole pairs generated per photon in the gas phase. From a wide range of reduction temperatures, titanium sub-oxime reduced at 400 oC showed the best performance in removing carbon dioxide. In the application of TiO2 for the built environment, the best commercially available TiO2 powder, anatase P25 was applied with two different techniques. Electrophoretic deposition has the potential to scale up the process for prefabricated panels in construction. Solvent, iv deposition time, voltage and substrate were optimised. The resulting photoactivity of the coatings was evaluated showing a higher efficiency than a compressed pellet of anatase P25. The final part of the thesis was dedicated to the formulation and application of a photocatalytic enhanced lime based coatings for the built heritage. The use of calcium hydroxide dispersions is widely used in the conservation and restoration community, reinforcing limestone when it carbonates. Anatase P25, was added to improve the performance in polluted atmospheres, acting as a sacrificial barrier. Results showed that by adding anatase to the formulation, calcium hydroxide reacted preferentially with sulphur dioxide over carbon dioxide. The final product in the formulation with anatase was calcium sulphate, whereas the final product for the calcium hydroxide formulation was calcium sulphite. Finally, a general discussion of the results is presented and the conclusions of this research are drawn. Recommendations for further work are presented in the last chapter.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:687320 |
| Date | January 2015 |
| Creators | Nuño, Manuel |
| Contributors | Ball, Richard ; Bowen, Christopher |
| Publisher | University of Bath |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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