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Title: Molecular adsorption on TiO2 surfaces : modelling potential biomedical and photovoltaic devices
Author: Syres, Karen Louise
ISNI:       0000 0004 2698 0983
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2010
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This thesis describes molecular adsorption on single crystal anatase (101) and rutile (110) TiO2 surfaces and TiO2 nanoparticles using photoemission and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. DFT calculations were carried out in order to complement the experimental data. The adsorption of dopamine and pyrocatechol on single crystal TiO2 surfaces was investigated with photoemission and NEXAFS and indicates the molecules adsorb in a bidentate mode following deprotonation of the hydroxyl groups. NEXAFS analysis of pyrocatechol adsorption on the rutile (110) and anatase (101) TiO2 surfaces shows the plane of the aromatic ring to be oriented at 23˚±8˚ and 27˚±6˚ from the surface normal, respectively. Dopamine adsorbed on the anatase TiO2 (101) surface was found to adsorb with the plane of the ring approximately normal to the surface. Adsorption of pyrocatechol and dopamine on anatase TiO2 (101) gave rise to a feature below the main pi* peak, not observed when pyrocatechol was adsorbed on rutile TiO2 (110). This feature was replicated in DFT calculations of both dopamine and pyrocatechol adsorbed on an anatase TiO2 cluster, but was not present in calculations of the free molecules. The new states are found to be located on the TiO2 surface, which may allow direct charge-transfer from the molecule to the surface. Simulated NEXAFS spectra from the cluster showed good agreement with the experimental data in the pi* region for the molecule-anatase TiO2 (101) system. The rutile experimental data showed good agreement with calculations of the free molecule in terms of the pi* peak separation. Charge-transfer studies of pyrocatechol adsorbed on the rutile TiO2 (110) surface indicate that charge-transfer could be occurring from the LUMO, LUMO+1 and LUMO+2 in the pyrocatechol molecule. The charge transfer time for this system was found to be < 9.0 ± 2.0 fs. XPS results for functionalised TiO2 nanoparticles show that dopamine (DA) molecules adsorb intact and bond through both oxygen atoms. The attachment of PEG (polyethylene glycol) and Pluronic was investigated. PEGme-DA (terminated with methyl) and DA-PEG-DA showed attachment to the nanoparticles occurs through one end of the chain. DA-Pluronic-DA may attach through both DA molecules but this could not be proved conclusively. Adsorption of malonic acid on rutile TiO2 (110) showed that the molecule degraded under the synchrotron beam and formed acetate and/or formate. It was found that dipping this surface into a ruthenium di-2,2'-bipyridyl-4,4'-dicarboxylic acid diisocyanate-dye solution in air appeared to displace the adsorbed species, replacing them with the dye.
Supervisor: Thomas, Andrew Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available