Black TiO2 NTs and ZnO-TiO2 NTs Heterostructure: Synthesis, Characterization, and Synchrotron-based Spectroscopy Studies

Lu Yao

Abstract

The one-dimensional (1D) TiO₂ nanotubes (NTs), and their derivatives have been extensively studied due to their potential use in water-splitting, solar cells, and lithium-ion batteries. Since TiO₂ has a large band gap (~3.2 eV for anatase), there has been a search for higher photocatalytic efficiency by shifting the band gap into the visible range. This thesis presents a study of black TiO₂ NTs and ZnO-TiO₂ heterostructures using synchrotron-based X-ray spectroscopy and X-ray diffraction techniques. It involves the transformation from as-prepared TiO₂ NTs to black TiO₂ NTs via an electrochemical reduction method. ZnO-TiO₂ NT heterostructures, designed to modify functionality with various preparation methodologies, are also explored. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) are used to track the morphology and crystalline structure of samples, respectively. Furthermore, the local and electronic structures of the elements in the samples are determined by X-ray absorption near-edge structure (XANES). Combined with X-ray excited optical luminescence (XEOL), X-ray emission spectroscopy (XES), and resonant inelastic X-ray scattering (RIXS) techniques, the electronic structure of the valence band, conduction band, and band gap, as well as the luminescence with respect to specific elemental and chemical environments (defects), can be explored.