Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Chemistry

Supervisor(s)

Tsun-Kong Sham

Abstract

One-dimensional (1D) TiO2 nanomaterials with ordered structure have been extensively applied in various fields, such as photocatalysts, solar cells, supercapacitors and rechargeable batteries, due to the unique structural and functional properties compared to the disordered nanoparticulate forms. Nevertheless, intrinsic disadvantages of TiO2, such as its large band gap (~3 eV), fast recombination rate of photoexcited electron–hole pairs and insufficient ionic conductivity, severely limit the development of 1D TiO2 nanomaterials for practical applications. To address the above issues, the scope of this thesis focus on the fundamental understandings of the electronic structure of highly ordered TiO2 nanostructures upon the anatase-to-rutile solid phase transition, anion doping, noble metal decoration and sodium ion intercalation, using synchrotron based X-ray absorption, emission and related microscopy and spectroscopies.

X-ray absorption near edge structure (XANES) in combination with scanning transmission X-ray microscopy (STXM) is used to track the rutile nucleation site and the associated rutile growth behavior of 1D TiO2 nanostructure. It is found that the bottom cap layer with its defective nature requires a lower thermal energy for rutile nucleation, and the growth of a dense rutile structure proceeds from the bottom to the top at the expense of nanostructured anatase TiO2. The unzipping of the top nanotube into nanograss structure can further stabilize the anatase phase structure. To increase the photoabsorption and photoperformance of TiO2, N-doped and Pd-decorated TiO2 nanotubes are prepared. On one hand, a TiO2-x anatase core warped by a Ti4O7 amorphous shell structure is achieved by N doping. The synergy for extraordinary photoabsorption established by this newly core-shell structure is revealed by XANES and resonant inelastic X-ray scattering (RIXS). On the other hand, the electronic and optical properties of Pd/TiO2 Schottky heterojunction have been thoroughly investigated using X-ray absorption fine structure (XAFS), X-ray excited optical luminescence (XEOL) and RIXS to elucidate its enhanced photoactivity. Finally, amorphous and anatase TiO2 nanotubes are comparatively studied for accommodating the sodium ion, of which XANES with its element and site specificities is applied to track the local effect of sodium uptake/release in TiO2 nanotubes.

Available for download on Monday, May 01, 2017


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