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Visible light induced photocatalytic decomposition of odorant compounds in drinking water

Casey, Helen Elizabeth (2017) Visible light induced photocatalytic decomposition of odorant compounds in drinking water. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

Geosmin and 2-methylisoborneol (MIB) are two taste and odour causing compounds commonly encountered in drinking water. The analytical identification and quantification of these important taste and odour compounds is required since they affect the organoleptic properties of drinking water and therefore the consumer perception and acceptability of drinking water. This thesis provides an up-to-date summary of analytical techniques for their identification and quantification. Furthermore, recent developments in the elimination of these target compounds are overviewed; conventional treatment methods such as coagulation, sedimentation, filtration and chlorination are ineffective and alternative successful methods are being sought. There is potential for new elimination technology to be implemented into water treatment facilities due to consumer demand. TiO2 thin films were produced from a magnetron sputtering technique, along with N-TiO2, Mo-TiO2 and Er-TiO2. All The films were characterised in terms of structure and composition using Scanning electron microscopy (SEM), Raman spectroscopy, X-ray diffraction (XRD), ultraviolet–visible spectroscopy (UV-Vis), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDX) and surface profilometry. Nitrogen-doped titania (N-TiO2) photocatalytic thin films were prepared by reactive magnetron sputter deposition. Nitrogen doping was achieved by the introduction of nitrogen gas as an additional reactive gas during sputtering. There was a distinctive shift of the absorption band in the N-TiO2 to longer visible regions of the electromagnetic spectrum. The photocatalytic performance was evaluated by mineralisation of geosmin and MIB. XPS revealed that 1% nitrogen doping resulted in reduction of the band gap energy, enabling 80% degradation of geosmin and MIB under visible light irradiation in 150 minutes. Titanium dioxide nanoparticles and titanium dioxide nanoparticles doped with nitrogen were produced via a sol gel method for direct comparison with the thin films to break down the T&Os, unfortunately many issues arise with using nanoparticles in drinking water treatment as the nanoparticles can leach into the water. A series of erbia doped titania (Er-TiO2) thin films photocatalysts were also deposited by powder magnetron sputtering method, this material has never been produced before. Erbia powder precursor ranging from 5 to 12.5 % were used to dope the titania films. The amount of erbia present in the TiO2 thin film was determined using inductively coupled plasma mass spectrophotometry (ICP-MS). Raman spectroscopy showed that the films were not crystalline and the broad peak positions obtained corresponded to a mixture of anatase and brookite crystalline forms. XPS analysis revealed that erbium was present in the form of an oxide. The experiments demonstrated that geosmin and 2-MIB in aqueous solutions was successfully degraded under visible light (> 450 nm) using Er-TiO2. The results demonstrate successful degradation of geosmin and MIB. These results show the feasibility of utilising the magnetron sputtering technique to grow films for industrial applications in new solar powered elimination technology for implementation in water treatment facilities.

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