Ng, Siow Woon
(2018)
ZnO And MoSexOy Modified TiO2 Nanotubes
For Photoelectrochemical And
Sensing Applications.
PhD thesis, Universiti Sains Malaysia.
Abstract
One-dimensional (1D) anodic self-organized TiO2 nanotube layers have attracted
considerable scientific and technological interest over a decade. The major drawbacks
are their rather wide band gap energies (3.0–3.2 eV) with high photoactivity only in the
ultraviolet (UV) spectral region (l � 390 nm, �5% of the solar spectrum), relatively
low conductivity and high carrier recombination rate. Furthermore, as a high aspect
ratio (HAR) nanostructure, the deposition of a uniform secondary coating within the
TiO2 nanotube layers remains a challenge. To overcome these critical issues, present
work is intended (i) to synthesize anodic 1D TiO2 nanotube layers as an independent
semiconductor and for the incorporation of secondary materials; (ii) to produce homogeneous
and conformal ZnO and MoSexOy coatings by atomic layer deposition (ALD)
within TiO2 nanotube layers; (iii) to form heterostructure in order to enhance charge
transport efficiency, increase light absorption and extend the functional range to the visible
spectral region; and (iv) to evaluate UV photodetection responses, ethanol sensing
responses at low temperatures, photocurrent generation and photocatalytic degradation
of methylene blue (MB). The synthesis of the TiO2 nanotube layers was carried
out by a conventional electrochemical anodization of Ti sheet in fluorinated organic
electrolytes. A low bias, visible-blind, UV photodetector was constructed in a sandwich
structure comprising of ITO/electrolyte/TiO2 nanotubes/Ti for the first time to
investigate the photodetection in UV-A, B and C spectral regions.
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