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Title: Surface and interfacial nanoscience of titanium dioxide
Author: Nadeem, Immad Muhammed
ISNI:       0000 0004 7659 9339
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2018
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Surfaces and interfaces of titanium dioxide (TiO2) are investigated with scanning probe microscopy and surface X-ray diffraction. A discussion on an experimental arrangement for in situ solid/liquid interface surface crystallography of UHV prepared samples is also presented. Water splitting on TiO2 is a promising candidate for photocatalytic H2 fuel production. In ultra-high vacuum (UHV), our scanning tunneling microscopy (STM) investigation on anatase TiO2 (101) (A101) suggests that surface oxygen vacancies can dissociate H2O by forming bridging OH species. Additionally, surface X-ray diffraction (SXRD) of the room temperature interface of A101 in contact with an ultra-thin water film or bulk water indicate that both interfaces contain a 25:75 mixture of molecular H2O and terminal OH bound to titanium atoms along with bridging OH species. This is in striking contrast to the inert character of room temperature A101 in UHV. An electrochemical surface science perspective of TiO2 is largely lacking. We present in situ STM and SXRD investigations of the rutile TiO2 (110) (R110) and electrolyte solution interface - chiefly 0.1 M NaOH and 0.1 M HCl. Our findings indicate that Na adsorbs at the surface tetra-dentate site between four oxygen atoms and the Cl adsorbs at the surface mono-dentate site bound to a Ti atom. Additionally, preliminary electrochemical STM measurements of R110 gives rise to terrace resolution images. This is a promising result for future electrochemical surface science on TiO2. Although the anatase/rutile interface is understood to play an important role in photocatalysis, surface science of TiO2 has largely been restricted to single crystal and thin film surfaces. In UHV, we present an STM tip manipulation procedure to form regions of rutile TiO2 (100) (R100) on A101 and thus create an anatase/rutile interface. Furthermore, UHV STM of photoactive carboxylic acid adsorption on R100 is presented for surface characterisation and to understand the photoactivity of R100. Acetic acid adsorption gives rise to a partially ordered overlayer with a (×2) periodicity in the [001] direction. Tri-methyl acetic adsorption is largely disordered.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available